Cell Calcium

Along with the membrane potential and respiration, mitochondrial matrix volume is a critical parameter that determines mitochondrial function. Mitochondria undergo constant changes in matrix volume and cristae dynamics, and in processes that are critical for normal metabolic rates and pathophysiological responses. Changes in matrix volume cannot be easily measured by conventional fluorescence imaging techniques due to the size of the sub-organellar structures, which are below resolution. This challenge was successfully resolved in studies of isolated mitochondria with the use of scattered light. Here we use dark-field imaging, which relies on scattered light contrast, to measure matrix volume dynamics in living cells. We demonstrate that mitochondrial volume changes can be easily detected as changes in intensity of the scattered light following matrix volume modulation with K+ ionophores or by onset of the permeability transition. Specifically, we found that stimulation of K+ influx leads to increase of mitochondrial matrix volume while stimulation of K+ efflux leads to matrix shrinkage, and that activation of the permeability transition leads to high-amplitude mitochondrial swelling in wild-type but not in cells lacking subunit c of ATP synthase. These results directly demonstrate the dynamic nature of mitochondrial matrix volume and its link to physiological and pathological ion transport.

Following ER Ca2+ depletion, Ca2+ release-activated Ca2+ (CRAC) channels are activated by STIM1 at ER-plasma membrane junctions. The restricted localization and low conductance of the CRAC channel (<40 fS) precludes single-channel recordings, limiting studies of CRAC channel gating. Here we describe an optical approach to characterize the gating of HaloTag-fused Orai1 channels labeled with JF646-BAPTA, a Ca2+-sensitive fluorescent dye. While Ca2+ influx through single channels generates fluorescence fluctuations, identifying true gating events is complicated by stochastic transitions of JF646-BAPTA to a non-fluorescent state. To overcome this, we combine TIRF microscopy with whole-cell voltage clamp to control the driving force for Ca2+ entry. We show the open channel intensity at -100 mV reflects Ca2+ saturation of the dyes on each channel, while the closed-channel intensity is defined by the fluorescence at +30 mV, where influx is absent. True gating events can be identified from transitions between the open- and closed-channel levels, distinguishing them from transitions to a non-fluorescent state. We describe the gating behavior of CRAC channels activated by STIM1 after store depletion. Dwell time distributions indicate at least two open and closed states with durations of 0.1 to several seconds, with most channels having an open probability of [&ge;]0.7. We also detect silent channels that colocalize with STIM1 but show no activity over tens of seconds, a population that would be undetectable by whole-cell electrophysiology alone. This method offers an approach to explore CRAC channel gating mechanisms and may be applicable to other Ca2+- permeable channels not amenable to patch-clamp techniques.

Aminoglycoside (AG) antibiotic safety is limited by ototoxicity, the mitigation of which is vital considering bacterial resistance mediated erosion of our antibiotic arsenal. Previously, we observed tectorial membrane (TM) sequestration of Ca2+. We hypothesized that the TM sequesters other cations, including the AG gentamicin. We proposed to test the effect of TM genetic ablation on ototoxicity and TM-AG sequestration. After intraperitoneal AG-furosemide, TM-lacking Tecta{Delta}ENT/{Delta}ENT mice showed limited outer hair cell loss, unlike wildtype littermates. Spectroscopy measurements of gentamicin-Texas red (GTTR) were made in isolated wildtype and TectaY1870C TMs and guinea pig cochleae following direct or intraperitoneal GTTR administration. TM-GTTR sequestration was observed in all cases, while negatively correlated with TectaY1870C zygosity. In summary, we discovered a novel TM component in the AG ototoxicity pathway. Intact TM structure is necessary for sequestration, and the TM modulates AG ototoxicity. TM-GTTR sequestration following systemic injection indicates that this phenomenon occurs during AG therapy. Single sentence summaryOtotoxic aminoglycosides collect inside the acellular tectorial membrane of the inner ear, likely due to electrostatic interactions, and the structural status of that membrane modulates the toxic effect of those aminoglycosides on sensory hair cells.

Muscle satellite cells (MuSCs) are muscle-resident stem cells that are responsible for myofiber regeneration. Although the importance of calcium ions (Ca2+) in muscle physiology has been well established, the mechanism by which Ca2+ mobilization governs MuSC function remains poorly understood. In this study, we aimed to systematically characterize Ca2+ dynamics in MuSCs and to define the mechanisms regulating these signals during muscle regeneration. By employing modified protocols for mouse MuSC isolation and Ca2+ measurement, we observed spontaneous Ca2+ fluctuations in MuSCs isolated from regenerating muscle after cardiotoxin-induced myofiber injury. Our detailed analysis using chemical Ca2+ indicators and a genetically encoded Ca2+ indicator revealed that the frequency and amplitude of Ca2+ fluctuations increased significantly during the activated and proliferative stages of MuSCs in muscle regeneration. This effect was more pronounced in MuSCs isolated from dystrophic and aged mice. Mechanistically, these Ca2+ fluctuations were at least partially mediated by mechanosensitive ion channels, including PIEZO1 and TRPM7, which promote MuSC migration. Collectively, our findings demonstrate that Ca2+ fluctuations through mechanosensitive ion channels act as a key regulator of MuSC activation during muscle regeneration and may provide new insights into the role of Ca2+ influx in muscle biology and the pathogenesis of muscle diseases.

Intracellular pH (pHi) dynamics regulates numerous cell behaviors, including migration and proliferation. While these functions are well-established in cell lines, the role of pHi changes in vivo is less well understood. We generated a transgenic zebrafish line expressing a fluorescent ratiometric pHi biosensor and identified functional changes in pHi during zebrafish larval tail regeneration. We found that tail amputation led to a transient decrease in pHi, followed by a prolonged increase in pHi above pre-amputation values. Moreover, we showed that pharmacologically inhibiting Na+/H+ exchanger (NHE) activity or decreasing extracellular pH attenuated the post-amputation increase in pHi, reduced subsequent cell proliferation, and impaired tail regeneration. We further found that inhibiting NHE activity post-amputation led to elevated inflammation, disrupted myeloid cell behavior, decreased reactive oxygen species, and increased glycogen synthase kinase-3 (GSK3) activity. Finally, we showed that the regeneration defects in larvae with disrupted pHi were partially rescued by the GSK3 inhibitor BIO. Our data reveal a previously unrecognized role for pHi dynamics in coordinating tissue behaviors in vivo and enabling zebrafish larval tail regeneration.

Synaptic failure and associated neuronal network dysfunction are key pathological processes involved in the early stages of Alzheimers disease (AD). A better understanding of the specific synaptic pathways and network topologies that drive disease vulnerability is therefore essential for the development of a targeted therapeutic intervention. In the present study, we aimed to determine how defined synaptic pathways and connectivity patterns shape the emergence and progression of the structural and functional network dynamics of human neuronal networks with inherent vulnerability to AD. We performed longitudinal microelectrode array recordings, assessed excitatory and inhibitory activity, quantified neurite growth, and performed proteomic analyses of synaptosomes from human induced pluripotent stem cell-derived neuronal networks carrying homozygous apolipoprotein E epsilon 4 (APOE4), the strongest genetic risk factor for developing late-onset AD. This integrated approach enabled multiscale characterization of synaptic alterations, structural maturation, and functional network dynamics associated with AD vulnerability. Compared to isogenic homozygous APOE3 networks, we found that APOE4 drives a distinct topological regime, characterized by high assortativity combined with low transitivity, which reflects a compensatory organization with reduced redundancy and flexibility, consistent with an intrinsically fragile network structure. APOE4 networks exhibited reduced firing rates, dynamic excitatory and inhibitory imbalance, impaired synchronization, absence of network bursting, and reduced global routing efficiency. Despite retaining small-world properties indicative of baseline information processing capacity, the topological and functional profile of APOE4 networks suggests a reliance on compensatory mechanisms associated with elevated metabolic cost and increased susceptibility to pathological spread. Structurally, APOE4 networks displayed reduced dendritic length, branching, and total dendrite area, accompanied by dysregulation of synaptic organization and signaling, ion dynamics, and intracellular signaling pathways. Together, these findings establish that APOE4 drives a multiscale reorganization of neuronal networks that not only mirrors synaptic alterations identified in patients, but also contextualizes these changes within network-level dynamics, advancing a more comprehensive understanding of early AD pathology.

Astrocytic homeostatic programs, many of which are regulated by the circadian clock, are disrupted early in neurodegenerative disease. The core clock transcription factor (TF) BMAL1 is required for normal astrocyte function, but its role during disease remains unclear. This is partly because methods for identifying cell type-specific TF binding sites are limited. Here, we developed MACS-Calling Cards (MACS-CC), a strategy for mapping astrocyte-specific TF occupancy in vivo. We used MACS-CC to define BMAL1 binding in the Cln3{Delta}ex7/8 mouse model of CLN3 disease, a fatal neurodegenerative disorder marked by early astrocyte dysfunction and circadian disruption. BMAL1 binding was extensively redistributed in Cln3{Delta}ex7/8 astrocytes: wild-type-specific binding sites enriched near glial differentiation genes, whereas Cln3{Delta}ex7/8-specific sites lacked functional enrichment. Consistent with these changes, Cln3{Delta}ex7/8 astrocytes decreased expression of mature astrocyte markers. To define mechanisms underlying BMAL1 retargeting, we tested whether altered chromatin accessibility explained the changes in BMAL1 binding. Although chromatin accessibility was broadly remodeled, differential accessibility did not predict BMAL1 redistribution. Instead, motif analysis suggested that loss of cooperative TF interactions drives BMAL1 retargeting. These findings demonstrate that MACS-CC enables astrocyte-specific TF occupancy mapping and reveals mechanisms behind early rewiring of circadian regulatory programs within a model of a neurodegenerative disease. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=80 SRC="FIGDIR/small/721783v2_ufig1.gif" ALT="Figure 1"> View larger version (22K): org.highwire.dtl.DTLVardef@1ada239org.highwire.dtl.DTLVardef@7564a3org.highwire.dtl.DTLVardef@122222forg.highwire.dtl.DTLVardef@1f2729c_HPS_FORMAT_FIGEXP M_FIG C_FIG

The heart maintains systemic perfusion through the coordinated function of its four chambers: the left and right atria and ventricles. Each chamber has distinct structural, functional, and molecular properties tailored to its role in circulation, which may result in chamber-specific differences in myofilament structure and regulation between atria and ventricles. To test this hypothesis, we employed muscle mechanics and X-ray diffraction to investigate functional and structural differences in porcine left atrial (LA) and left ventricular (LV) tissue. Here, we report the first X-ray diffraction study of atrial tissue, demonstrating that under resting conditions, myosin filaments in LA adopted a more ON-like, structurally distinct configuration compared with those in LV. Under contracting conditions, LV generated greater force and exhibited higher sinusoidal stiffness than LA across multiple calcium concentrations. LA showed faster kTR than in LV, with no calcium-dependence, in contrast to the calcium-dependence of kTR seen in LV. Structurally, the distinct myosin head configuration seen in the relaxed LA persisted during contraction. Furthermore, using the troponin inhibitor MYK-7660 to inhibit active contraction, we showed that, unlike LV, LA showed no direct calcium-dependent thick filament activation, reconciling discrepancies between fast rat and slow porcine ventricular myocardium regarding calciums role in thick filament regulation. Altogether, our study reveals that LA myosin filaments adopt a molecular architecture and regulatory mechanism distinct from their LV counterparts, suggesting that myosin filament structure and regulation have evolved differently to meet the unique functional demands of each cardiac chamber. Moreover, atrial disease is often associated with cardiomyopathy-related genetic variants, highlighting the atrial myocardium as an important therapeutic target and understanding atrial-specific regulatory mechanisms provides new insights into therapeutic strategies for atrial diseases.

Growing interest to describe the electrical behavior of glial cells, mainly astrocytes, in intact brain tissue poses more and more challenges to commonly accepted belief they only respond in a linear manner in uptake of the excess of extracellular potassium and maintenance of their network equipotentiality. Their highly conductive mutual interconnections via gap junction (GJ) connections introduce yet another class of nonlinear elements. As more studies report nonlinearities in membrane voltage Vm dependence of both, the membrane and junctional conductances, the need to formulate minimal dynamical models of their transient behavior is getting more acute. Since ODE models of coupled cells, even in simplest 1-d arrays, require simplified descriptions and small set of parameters, rare quantitative studies on glia makes the task even more difficult. This study attempts to qualify a self-coupled cell, or a glial cell coupled to fixed voltage as useful system for detecting the nature of instabilities and transitions coming from coupling. In a novel biophysical model of coupled astrocyte, we introduce nonlinear kinetics of deactivation for large junctional voltages for the first time. We found that N-shaped nonlinearities and corresponding fold structure in the vector field of isolated cell serves as a baseline on top of which coupling nonlinearities enrich the bifurcation picture. Numerical simulations of 1-d array of coupled astrocytes show that coupling increases the propensity of astrocytic Vm to bistability and front propagation. We believe that presented illustrations of possible effects of coupling nonlinearities will motivate neurobiologists to further explore their impact in disease. Significance statementTransient changes in membrane voltage of glial cells may produce significant transient voltage difference between directly coupled cells. Nonlinear steady-state conductance of their interconnection elements, the gap junctions, introduce nonlinear current profiles which are very difficult to measure and quantitate using the available methods due to marked permeability of the junctions and leakiness of glial membrane in general. We propose a minimal model of glial membrane extended with a self-coupled feedback loop, which under realistic simplifying assumptions could serve for qualitative analysis of the impact of coupling, on the stability of resting membrane voltage. Neuronal cells of the brain and spinal cord cannot exist and function without supportive and neuromodulatory functions of the diverse population of glial cells. This applies to virtually all physiological processes on cell level - from cell development, metabolic support, membrane signaling, slow molecular signal transduction, ion homeostasis, neurovascular coupling, myelination, to mention only a few, manifest neuro-glial interaction. Even though all glial cell types are interconnected, the most abundant ones, the astrocytes are massively interconnected by gap junctions to form ordered networks. Electrically, astrocytic networks display membrane voltage equipotentiality, which is considered system-wide resting state for given neuro-glial circuit or unit. With molecular and cellular substrates of glial connectivity being slowly elucidated, network science and dynamical modeling are slowly "invading" that area with many important issues left open. In this study using classical dynamical systems approaches we give indications how nonlinear intercellular coupling between astrocytes affects physiological resting state and its instabilities compared to isolated, uncoupled cell. We strongly believe the suggested minimal model could fill the gap in ODE modeling of neuro-glial circuits, within broadest scope of hypothesis-driven research in cell-level neuroscience.

SCN2A-related disorders result from pathogenic variants in the gene encoding for the voltage-gated sodium channel Nav1.2. Collectively, these disorders result in variable age of onset epilepsy, autism spectrum disorder, and epileptic encephalopathies. While the mechanisms of haploinsufficiency resulting in autism spectrum disorder have been explored in detail, few studies report the impact of pathogenic missense variants in human neurons. In this work, we combined conventional electrophysiology and high-throughput all-optical electrophysiology assays to analyze the SCN2A p.M1879T pathogenic variant associated with early-onset epilepsy and developmental delay. In both platforms, iPSC-derived excitatory neurons expressing the disease variant showed greater firing at higher stimuli compared to the isogenic control neurons (corrected by CRISPR/Cas9), as well as changes to action potential shape (steeper slope and larger amplitude) with evoked firing. We used machine learning techniques on the optical physiology dataset to classify the two genotypes, finding that sodium channel blocking anti-seizure drugs could restore an isogenic phenotype. This work demonstrates proof of sodium channel blocker efficacy in a human neuronal model of SCN2A-related epilepsy and highlights the power of leveraging high-throughput all-optical electrophysiology for testing drug efficacy.

A growing number of studies indicate the possible involvement of astrocytes in triggering or modulating neurovascular coupling (NVC), i.e. the local dilation of blood vessels in the brain in response to neuronal activity. Astrocytes possess specialized subcellular compartments, named endfeet, that surround arterioles and capillaries, ideally positioned to mediate NVC. Various vasodilators have been shown to contribute to NVC, such as epoxyeicosatrienoic acid (EET), nitric oxide (NO), or prostaglandin E2 (PGE2), but the precise mechanisms underlying NVC and their variability remain to be fully elucidated. In particular, the involvement of astrocytes in this process is controversial. Recent translatome and proteomics data reveal that astrocytes and in particular endfeet are enriched in the proteins of the PGE2 pathway. However, how the latter could contribute to NVC remains to be characterized. Here, we develop a computational model of astrocyte-mediated NVC that recapitulates these findings and describes Ca2+ and PGE2 signaling in astrocytes, NO release by neurons, and arteriole diameter dynamics using ordinary differential equations. The model successfully reproduces the dynamics of arteriole diameter change during hyperemia from in vivo neocortical recordings in awake mice. Our simulations suggest that the astrocyte PGE2 pathway could be responsible for the late response of NVC at the arteriolar level. We further observe that PIP2-derived diacylglycerol plays a major role in driving arteriole diameter dynamics in our model, while phosphatidic acid-derived diacylglycerol, which is calcium-dependent, mainly acts as an amplifier of this response. Finally, a spatial implementation of the model using a simplified astrocyte geometry suggests that NVC is more efficient when synaptic stimulation occurs at the endfoot level rather than at other astrocytic compartments. Overall, this computational study suggests a partial role for astrocyte-mediated PGE2 release in NVC and points to astrocyte perivascular processes as sub-compartments that are ideally positioned and equipped to mediate NVC. Author summaryIn the brain, the local blood flow is regulated to meet neuronal energy demand by modulating the dilation of neighboring blood vessels. The mechanisms driving this process, known as neurovascular coupling (NVC), remain debated and are likely to differ depending on the physiological context. Recent evidence points to astrocytes, a cell type possessing specialized protrusions called "endfeet", that envelop the entire brain vascular tree. Contacts between synapses and endfeet have recently been reported, positioning the latter as ideal mediators of NVC. Here, we developed a computational model that simulates the signaling between neurons, astrocytes, and blood vessels. Our model successfully reproduces experimental recordings of blood vessels dilation in the brains of awake mice. Our simulations suggest that a specific signaling pathway in astrocytes, involving a molecule called prostaglandin E2, is a key driver of the late phase of NVC, occurring a few seconds after neuronal activity. Furthermore, our model indicates that the location of the stimulated synapses matters: signals sent to the astrocyte endfeet are particularly effective at controlling blood flow. This work helps clarify the active role of astrocytes in brain blood flow regulation, a process critical for healthy brain function.

Phosphatidylinositol (4,5)-bisphosphate (PIP2), the most abundant cellular poly-phosphoinositide (PPI) class of phospholipid, is a central plasma membrane (PM)-associated signaling hub that controls many cellular processes. In this study, we demonstrate that either deletion of the gene encoding actin-binding protein profilin1 (Pfn1) or disruption of Pfn1-actin interaction leads to downregulation of PM PIP2 content in cells. This is also phenocopied when F-actin is depolymerized implying that Pfn1-dependent PIP2 alteration is related to its actin-regulatory function. Phospholipase C (PLC) activity is critical for Pfn1-deficient cells to exhibit the PIP2-related phenotype. These findings, taken together with biochemical signatures of elevated PIP2 hydrolysis (higher baseline PM diacylglycerol-to PIP2 ratio and protein kinase C activity) exhibited by Pfn1-deficient cells, imply that PLC-mediated PIP2 hydrolysis plays a role in Pfn1-dependent regulation of PM PIP2. Furthermore, we unexpectedly found that Pfn1 loss leads to dramatic alterations in several other important forms of lipids, revealing a previously unrecognized role of Pfn1 as a broad regulator of cellular lipid environment that extends beyond PPI control. In conclusion, our study establishes Pfn1 as an important regulator of cellular lipid homeostasis. SUMMARY STATEMENTThis study uncovers a mechanism of how functional loss of Profilin1, a key regulator of actin cytoskeleton, can trigger downregulation of plasma membrane content of PIP2, an important class of phospholipid, in cells.

Neurons maintain functionality through homeostatic regulation of spiking activity over extended timescales. Calcium dependent conductance expression is known to regulate mean firing rate, but this is not sufficient to ensure dynamic range in spiking activity and sensitivity to input. This raises the question of whether firing rate variance can be sensed and controlled intracellularly. Using conductance-based models, we demonstrate that time-averaged intracellular calcium dynamics inherently provide a direct readout of both the mean and variance of spiking activity. We show that calcium-based feedback regulation of membrane conductance density can therefore jointly stabilize firing rate mean and variance against input disturbances. Because tuning maximal conductances modulates the underlying relationship between rate statistics, a cells homeostatic response is statedependent rather than fixed. As a consequence, cell-type-specific mixtures of ionic conductances yield distinct homeostatic modalities, implying that cell type dictates homeostatic behaviour as well as spiking and integrative properties.

Electrical transmission is mediated by intercellular channels that cluster into structures known as gap junctions (GJ). In vertebrates, GJ channels are encoded by the gene family of connexin (Cx) proteins that assemble as hexamers, termed hemichannels, in the pre- and postsynaptic membranes, and that subsequently dock to form GJ channels. Auditory contacts on the fish Mauthner cells serve as model to study the properties and organization of vertebrate electrical synapses. Electrical transmission at these synapses is mediated by multiple co-existing GJs at which the presence of intercellular channels is regulated by a molecular scaffold. Zebrafish contain four homologs of the neuronal Cx36: Cx35.5 and Cx35.1 (gjd2a and b, respectively), and Cx34.1 and Cx34.7 (gjd1a and b). Cx mutations suggested that GJs are formed by heterotypic channels made of presynaptic Cx35.5 and postsynaptic Cx34.1. Using transgenic fish in which Cxs were tagged, we found that a second Cx, Cx34.7, is present together with Cx34.1 on the postsynaptic side at some but not all GJs at these terminals. When exogenously expressed, both Cx34.1 and Cx34.7 formed heterotypic functional channels with Cx35.5, each with substantially different voltage-dependent properties, indicating they can serve differential functions. However, we previously demonstrated that electrical transmission is lost in Cx34.1 but not Cx34.7 null mutants, suggesting that Cx34.7 cannot compensate for the loss of Cx34, despite the intrinsic ability of Cx34.1 and Cx34.7 to create functional channels. The findings reveal an unanticipated functional organization in the electrical synapse, where Cx34.1 is obligatory and Cx34.7 accessory, roles that appear to be defined by the postsynaptic molecular scaffold, with two postsynaptic Cxs possibly assembling under specific functional contexts. Thus, our results indicate that electrical synapses share an organizational motif with chemical synapses, akin to how they combine postsynaptic receptor types to modify synaptic function.

Understanding the behavior of - and {beta}-cells within intact human islets is essential for elucidating mechanisms of metabolic control in diabetes. Current cell-type identification strategies rely on destructive labeling or on advanced imaging modalities such as Fluorescence Lifetime Imaging Microscopy (FLIM), which provide rich metabolic information but require specialized instrumentation and acquisition protocols. Here we show that structured intracellular intensity patterns derived from endogenous autofluorescence are sufficient to discriminate and {beta} cells in living human islets. Using rotation-invariant Local Ternary Pattern (LTP) descriptors combined with morphological features, we achieve highly accurate classification (AUC = 0.92), improving upon previously reported benchmarks. The resulting framework is lightweight, interpretable, and compatible with standard imaging configurations, enabling accessible and scalable analysis of label-free microscopy data. Interpretability analyses demonstrate that discrimination is driven predominantly by fine-scale intracellular intensity organization rather than global morphology. In the spectral window employed, cytoplasmic autofluorescence is prominently shaped by lipofuscin-rich granules. Consistent with prior reports of higher lipofuscin accumulation in {beta}-cells, the dominant features identified here likely reflect differences in granule abundance and spatial organization between endocrine cell types. These findings indicate that endogenous intensity patterns encode sufficient structural information for reliable /{beta} discrimination, providing a biologically grounded and fully non-destructive framework for the identification of pancreatic islet cell types.

Conventional extracellular epithelial electrophysiology measurements report only bulk transepithelial resistance and capacitance, obscuring the distinct electrical properties of the apical and basolateral membranes. This limitation hinders research of epithelial diseases where dysfunction originates at a specific membrane domain--apical or basolateral--for example in cystic fibrosis or toxin-mediated airway injury. Here we present the extracellular electrochemical impedance spectroscopy (EEIS) technique that extracts membrane-specific electrophysiology by fitting impedance spectra to a two-resistor, two-capacitor (RCRC) model. Using human bronchiolar epithelial monolayers (16HBE), we show a correlation between the electrical time constants of the circuit ({tau}1 = R1 {middle dot} C1,{tau} 2 = R2 {middle dot} C2) and changes in ion permeability of the basolateral and apical membranes. Experimentally, we show that blocking with 5-10 {micro}M GlyH-101 (i.e. decreasing apical membrane permeability), after 10 {micro}M forskolin activation elicits dose dependent{tau} 2 responses that are over 50% larger than{tau} 1and 6-7 minutes faster, whereas 10 {micro}M nystatin (i.e. increasing basolateral membrane permeability) produces{tau} 1 responses 21-25% larger than{tau} 2 and approximately 2 minutes faster. For cystic fibrosis epithelia, we find that elexacaftor/tezacaftor/ivacaftor (ETI) restores the apical membrane electrical response, resulting in a significant 84% higher{tau} 2 than{tau} 1 within the first 10 minutes. It also exhibits a greater than 8 min faster{tau} 2 response relative to{tau} 1 following 10 {micro}M GlyH-101 blocking (i.e., decreasing apical membrane permeability). These results demonstrate that EEIS enables rapid, quantitative, and biologically relevant measurement of apical and basolateral membrane properties in 16HBE epithelia. By providing membrane-specific resolution without the experimental challenges of intracellular electrodes, EEIS establishes a general framework for rapid, membrane-resolved electrophysiology with implications for therapeutic screening.

Membrane-targeting antimicrobials are generally assumed to kill bacteria through bacteriolysis induced by the permeabilisation of the cytoplasmic membrane. This model relies on the notion that bacteriolysis is the direct cellular manifestation of the membrane-disruptive (membranolytic) activity of an antibacterial compound. However, it underappreciates the key role of peptidoglycan hydrolases in bacteriolysis. Using the Gram-positive model organism Bacillus subtilis, we demonstrate that the bacteriolytic activity of membrane-targeting antimicrobials arises from the misregulation of peptidoglycan hydrolases, regardless of whether they induce large membrane pores or trigger more subtle membrane disturbances such as depolarisation. Contrary to previous models, the autolysis of B. subtilis induced by membrane depolarising compounds does not depend on pH changes associated with the cell surface. Instead, the autolytic process is triggered by membrane depolarisation-dependent dissociation of the bacterial actin homolog MreB, a key spatial coordinator of cell wall synthesis in rod-shaped bacteria, from the cytoplasmic membrane. These findings provide valuable insights into the cellular pathways involved in autolysis, highlight the challenges in distinguishing between direct and indirect cellular effects of membrane-targeting antibiotics, and improve our understanding of antibiotic-induced bacteriolysis.

Pregnancy is a period of extensive metabolic rewiring. Insulin secreting {beta}-cells respond to the metabolic challenges of pregnancy by increasing their mass and size and by altering secretory patterns to maintain glucose homeostasis. If glucose metabolism is not tightly controlled, gestational diabetes may develop. Most studies on {beta}-cell adaptation during pregnancy are derived from rodent models, making translation to the vastly different human gestational setting challenging. In this work, we performed an extensive characterization of pancreatic adaptations throughout porcine pregnancy. Pigs have a long gestational period (114 days) and share a similar size and metabolism to humans, making them an ideal model to bridge the knowledge gap between rodents and humans. By analyzing pancreatic samples from early and late gestational ages, we captured the full trajectory of endocrine remodeling. We observed pregnancy-driven remodeling of endocrine cell types, marked by preferential expansion of pancreatic polypeptide-secreting cells. Proteomic characterization of the pancreas from early and late gestation showed a downregulation of SLC20A2 and ZCCHC7, identifying new protein targets involved in physiological endocrine cell adaptation. Overall, our comprehensive characterization of pancreatic adaptations in the pig model helps bridge the translational gap between rodents and humans and highlights previously unrecognized proteins with therapeutic potential for gestational diabetes.

Two crystallographic states of mechanosensitive TREK/TRAAK K2P channels - a low-activity down-state and a high-activity up-state - have been proposed to underlie gating, but the origin of the low activity remains debated. Competing models suggest either lipid-mediated pore block or selectivity filter (SF) inactivation. Using systematic mutagenesis of M2/M4 helices, we identified 16 highly active mutants and assessed their activation mechanisms via free-energy calculations, molecular dynamics simulations, and a state-dependent pharmacological probe. The computational approaches reliably predicted mutation-induced shifts in the down-up equilibrium. We further show that intracellular acidification and regulatory lipids primarily stabilize the up-state, consistent with stretch, temperature, and dephosphorylation. These findings support the down-up transition as the principal physiological activation pathway and suggest that mechanosensitivity arises from the larger membrane footprint of the up-state. Our data argue against a physiological role of a lipid-blocked pore and instead support gating via conformational control of the SF in TREK/TRAAK channels.

Iron absorption in the small intestine has classically been described by the duodenal DMT1/FPN1 pathway for inorganic non-heme iron, yet emerging evidence suggests that chemically distinct iron forms may use region-specific routes. Nicotianamine (NA), a plant-derived metal chelator, can form NA-iron (NA-Fe) complexes and has been proposed to support intestinal iron absorption through amino acid transporter pathways. However, direct comparisons of transepithelial transfer of inorganic iron and NA-Fe across defined small intestinal regions under controlled epithelial conditions remain limited. Here, we established region-specific 2D epithelial monolayers derived from duodenal and proximal jejunal crypt organoids from male ICR mice cultured on Transwell inserts. Transcriptomic profiling indicated partial retention of regional identity, and barrier integrity was confirmed by junctional marker localization, transepithelial electrical resistance, and low paracellular permeability. We then examined expression and polarized localization of candidate transporters for inorganic iron (Dmt1/Fpn1) and NA-Fe (Pat1/Lat2). Finally, we quantified transepithelial transport using apical loading of isotope-labeled iron (55Fe) or NA-55Fe and measured radioactivity appearing in the basolateral compartment as the primary readout of transepithelial flux. Basolateral appearance of inorganic 55Fe was comparable between duodenum- and proximal jejunum-derived monolayers, whereas NA-55Fe exhibited significantly greater basolateral appearance in proximal jejunum-derived monolayers. These findings demonstrate that organoid derived, region-specific monolayers provide a tractable epithelial platform to evaluate iron form-dependent, region-specific transepithelial transfer and to enable further mechanistic dissection of NA-Fe transport. NEW & NOTEWORTHYNon-heme iron absorption may depend on iron chemical form and intestinal region, but direct epithelial comparisons are scarce. We established duodenum and proximal jejunum derived murine intestinal organoid monolayers on Transwells and quantified transepithelial flux using isotope-labeled iron. Inorganic 55Fe showed no clear regional difference, whereas NA-55Fe displayed greater basolateral appearance in proximal jejunum-derived monolayers. This platform enables mechanistic studies of NA-iron complex transport.