Journal of Biophotonics

The photoacoustic effect refers to the generation of pressure waves in matter stimulated by light[1]. In the context of radiology (i.e., photoacoustic imaging) waves generated by pulsed laser light are detected by an ultrasound transducer[2-4]. It has been shown that photoacoustic waves produce a mechanical, tactile sensation in humans on bare skin[5]. In a series of psychophysical experiments, performed with both medical grade and off-the-shelf pulsed light systems, participants could detect, categorically describe, and discern the direction of travel of pulsed optical stimuli with the use of a dye as an optical absorber on the skin. To a large extent, the sensations were perceived as localized vibration on the glabrous surface of the fingers, when sensitized with the thin film of dye. This form of sensory stimulation demonstrates an enhanced non-contact, non-optogenetic, in situ activation of the mechanosensory system. This modality of sensation may provide a tool that leads to new insights in psychology, neuroscience, mechanobiology, and the health sciences. Finally, it has many advantageous characteristics for human interaction with artificial environments, as optical signals can be projected onto the skin across distances.

This study proposes a novel optical method of detecting and reducing SARS-CoV-2 transmission, the virus responsible for the COVID-19 pandemic that is sweeping the world today. SARS-CoV-2 belongs to the {beta}-coronaviruses characterized by the crown-shaped spike protein that protrudes out of the virus particles, giving the virus a "corona" shape; hence the name coronavirus. This virus is similar to the viruses that caused SARS (severe acute respiratory syndrome) and MERS (Middle East respiratory syndrome), the other two coronavirus epidemics that were recently contained within the last ten years. The technique being proposed uses a light source from a smart phone and a mobile spectrophotometer to enable detection of viral proteins in solution or paper as well as protein-protein interactions. The proof-of-concept is shown by detecting soluble preparations of spike protein subunits from SARS-CoV-2, followed by detection of the actual binding potential of the spike protein with its host receptor, the angiotensin-converting enzyme 2 (ACE2). The results are validated by showing that this method can detect antigen-antibody binding using two independent viral protein-antibody pairs. The binding could be detected optically both in solution and on a solid support such as nitrocellulose membrane. Finally, this technique is combined with DC bias to show that introduction of a current into the system can be used to disrupt the antigen-antibody reaction, suggesting that the proposed extended technique can be a potential means of not only detecting the virus, but also reducing virus transmission by disrupting virus-receptor interactions electrically. SignificanceThe measured intensity of light can reveal information about different cellular parameters under study. When light passes through a bio-composition, the intensity is associated with its content. The nuclei size, cell shape and the refractive index variation of cells contributes to light intensity. In this work, an optical label-free real time detection method incorporating the smartphone light source and a portable mini spectrometer for SARS-CoV-2 detection was developed based on the ability of its spike protein to interact with the ACE2 receptor. The light interactions with control and viral protein solutions were capable of providing a quick decision regarding whether the sample under test was positive or negative, thus enabling SARS-CoV-2 detection in a rapid manner.

Extracting biological information from awake and unrestrained mice is imperative to in vivo basic and pre-clinical research. Accordingly, imaging methods which preclude invasiveness, anesthesia, and/or physical restraint enable more physiologically relevant biological data extraction by eliminating these extrinsic confounders. In this article we discuss the recent development of shortwave infrared (SWIR) fluorescent imaging to visualize peripheral organs in freely-behaving mice, as well as propose potential applications of this imaging modality in the neurosciences.

The functional status of vessels can be determined by assessing blood perfusion. By integrating diffuse reflectance spectroscopy (DRS) and laser Doppler Flowmetry (LDF), the speed-resolved blood perfusion and blood oxygen saturation can be measured simultaneously by Enhanced Perfusion and Oxygen Saturation (EPOS). The dataset presented in this descriptor contains EPOS data recorded from a forearm point exposed to different levels of thermal stimulation, the classical LDF at control points, the R-R time series and data regarding characteristics of subjects. All data were recorded from 60 recruited healthy subjects. Half of the subjects received different levels of thermal stimulation, and half of them were blank controls. We believe that this dataset will lead to the development of local blood perfusion methods that can be used to index vessel function assessments. This publicly available dataset will be beneficial to the microcirculation evaluation.

Precise investigation of the temperature and the duration for collagen denaturation is critical for a number of applications, such as adjustment of temperature and duration during a laser-assisted tissue welding or collagen-based tissue repair products (films, implants, cross-linkers) preparation procedures. The result of such studies can serve as a guideline to mitigate potential side effects while maintaining the functionality of the collagen. Though a variety of collagen denaturation temperatures have been reported, there has not been a systematic study to report temperature-dependent denaturation rates. In this study, we perform a set of experiments on type-I collagen fiber bundles, extracted from the rat-tail tendon, and provide an Arrhenius model based on the acquired data. The tendons are introduced to buffer solutions having different temperatures, while monitoring the contrast in the crimp sights with a wide field microscope, where collagen fibers bend with respect to their original orientation. For all tested temperatures of 50{degrees}C-70 {degrees}C and tissues that were extracted from 5 rats, increasing the temperature reduced the contrast. On the average, we observed a decay of the contrast to half of its initial value at 37, 157, and 266 seconds when the collagen was introduced to 70 {degrees}C, 65 {degrees}C, and 60 {degrees}C buffer solutions, respectively. For the lower temperatures tested we only observed to be only about 20% and 2 % decay in the crimp contrast after > 2 hours at 55 {degrees}C and 50 {degrees}C, respectively. The observed denaturation behavior is also in line with Arrhenius Law, as expected. We are looking forward to expand this study to other types of collagen as a future work. Overall, with further development the data and model we present here could potentially serve as a guideline to determine limits for welding and manufacturing process of collagen-based tissue repair agents.

Traumatic Brain Injury (TBI) arises from an external force affecting the brain, leading to a range of outcomes from mild to severe. Despite continuous scientific advancements, it continues to pose a persistent threat and remains a significant cause of physical impairment and mortality. Various models, including blast-induced TBI (bTBI), have been proposed to simulate TBI. Laser-induced shockwaves (LIS) us emerging as an effective method. LIS generates shockwaves via pulsed laser-induced plasma formation, offering a controlled means to study TBI at the cellular level. Astrocytes, pivotal in maintaining brain function post-injury, undergo dynamic morphological changes, contributing to the understanding of injury responses and neurodegenerative diseases. This study introduces a system combining Laser-Induced Shockwaves (LIS) and Quantitative Phase Microscopy (QPM) to quantify morphological changes in astrocytes during and after LIS exposure. QPM, a label-free method, facilitates 3D imaging and captures real-time cellular dynamics. The integration of LIS and QPM enables the assessment of astrocyte responses to shear stress caused by LIS, revealing immediate and sustained morphological transformations. Analysis post-LIS exposure indicates significant alterations in circularity, volume, surface area, and other features. Statistical tests affirm of observed trends, providing insights into astrocyte responses to mechanical forces. The findings contribute to understanding how mechanical stimuli impact astrocyte morphology, holding promise for targeted therapeutic strategies in traumatic brain injuries and related neurological disorders. The integrated LIS and QPM approach serves as a powerful tool for 3D imaging and quantitative measurement of astrocyte morphological changes, offering deeper insights into cellular dynamics and potential therapeutic interventions.

As discussed below cataract is the world-leading cause of blindness and impaired vision with only eye surgery as a treatment. There is major requirement for an alternative which this research has provided via Genetically Modified pigs with natural cataract making live animal experiments of LED photobleaching successful monitored by fluorescence spectra. The latter were shown by EBS as spectrally identical in pigs and humans. EBS developed a miniature fluorescence spectrometer via tunable interference filters with fluorescence excited by an LED. A second LED in the blue/violet region provided a 20mW treatment beam which was shown to reverse the fluorescence signal and dramatically improve the transmission of pigs eyes. These results led to permission for early Human Trials. The results were judged by independent optometrists by LOCS and fluorescence in pigs and in Human Trials by LOCS and Visual Acuity. Adequate positive results have led to full length Human Trials being conducted in four European countries. Prospects of worldwide application have been therefore indicated.

A multicontrast polarimetric wide-field second harmonic generation (SHG) and multiphoton excitation fluorescence (MPF) microscope is optimized for large area imaging of hematoxylin and eosin (H&E) stained and unstained histology slides. The bleaching kinetics of MPF and SHG are examined with various laser intensities at different pulse repetition rates to determine the optimal wide-filed imaging conditions for H&E stained histology slides. Several polarimetric parameters are used to investigate the organization of extracellular matrix collagen in the histology samples.

Molecules capable of emitting a large number of photons (also known as fortunate molecules) are crucial for achieving resolution close to a single molecule limit (the actual size of a single molecule). We propose a long-exposure single molecule localization microscopy (leSMLM) technique that enables detection of fortunate molecules, which is based on the fact that detecting a relatively small subset of molecules with large photon emission increases its localization [Formula]. Fortunate molecules have the ability to emit a large burst of photons over a prolonged time (> average triplet-state lifetime). So, a long exposure time allows the time window necessary to detect these elite molecules. The technique involves the detection of fortunate molecules to generate enough statistics for a quality reconstruction of the target protein distribution in a cellular system. Studies show a significant PArticle Resolution Shift (PAR-shift) of about 6 nm and 11 nm towards Single-molecule-limit (away from diffraction-limit) for an exposure time window of 60 ms and 90 ms, respectively. In addition, a significant decrease in the fraction of fortunate molecules (single molecules with small localization precision) is observed. Specifically, 8.33% and 3.43% molecules are found to emit in 30 - 60 ms and 60 - 90 ms, respectively, when compared to SMLM. The long exposure has enabled better visualization of Dendra2HA molecular cluster, with sub-clusters within a large cluster. Thus, the proposed technique (leSMLM) facilitates a better study of cluster formation in fixed samples. Overall, the method enables better spatial resolution at the cost of relatively poor temporal resolution.

Photobiomodulation (PBM) is a novel technique that is actively studied for neuromodulation. However, despite the many in vivo studies, the stimulation protocols for PBM vary amongst studies, and the current understanding of neuromodulation via PBM is limited in terms of the extent of light penetration into the brain and its dosage dependence. Moreover, as near-infrared light can be absorbed by melanin in the skin, skin tone is a highly relevant but under-studied variable of interest. In this study, to address these gaps, we use Monte Carlo simulations (with MCX) of a single laser source for transcranial (tPBM) and intranasal (iPBM, nostril position) irradiated on a healthy human brain model. We investigate wavelengths of 670, 810 and 1064 nm in combination with light ("Caucasian"), medium ("Asian") and dark ("African") skin tones. Our simulations show that a maximum of 15% of the incidental energy for tPBM and 1% for iPBM reaches the cortex from the light source at the skin level. The rostral dorsal prefrontal cortex in tPBM and the ventromedial prefrontal cortex for iPBM accumulates the highest highest light energy, respectively for both wavelengths. Specifically, the 810 nm wavelength for tPBM and 1064 nm wavelength for iPBM produced the highest energy accumulation. Optical power density was found to be linearly correlated with energy. Moreover, we show that "Caucasian" skin allows the accumulation of higher light energy than other two skin colours. This study is the first to account for skin colour as a PBM dosing consideration, and provides evidence for hypothesis generation in in vivo studies of PBM.

Super-resolution (SR) microscopy is a cutting-edge method that can provide detailed structural information with high resolution. However, the thickness of the specimen has been a major limitation for SR methods, and larger structures have posed a challenge. To overcome this, the key step is to optimize sample preparation to ensure optical homogeneity and clarity, which can enhance the capabilities of SR methods for the acquisition of thicker structures. Oocytes are the largest cells in the mammalian body and are crucial objects in reproductive biology. They are especially useful for studying membrane proteins. However, oocytes are extremely fragile and sensitive to mechanical manipulation and osmotic shocks, making sample preparation a critical and challenging step. We present an innovative, simple, and sensitive approach to oocyte sample preparation for 3D STED acquisition. This involves alcohol dehydration and mounting into a high refractive index medium. This extended preparation procedure allowed us to successfully obtain a unique 2-channel 3D STED super-resolution image of an entire mouse oocyte. By optimizing sample preparation, we can overcome the limitations of SR methods and obtain high-resolution images of larger structures, such as oocytes, Knowledge of which are important for understanding fundamental biological processes. RESEARCH HIGHLIGHTSO_LIThis study aimed to develop a successful sample preparation protocol for imaging mouse oocytes using 3D STED super-resolution microscopy. C_LIO_LIThe results showed that the oocyte sample was optically homogenous, enhancing the capability of the 3D STED method to capture high-resolution images throughout the full depth of the sample, resulting in highly similar SR images. C_LIO_LIThe 3D STED point spread function (PSF) pattern of the depletion laser was successfully secured throughout the entire volume of the sample, including the top and bottom. C_LIO_LIThis study presents the first-ever full volume 3D image of the mouse oocyte, which was acquired using a 2-channel 3D STED method. C_LI GRAPHICAL ABSTRACTIntroducing an extended sample preparation procedure resulted in an outstanding optical quality sample environment pronounced by high refractive index, high transparency, and minimal spherical aberration. This procedure allowed 3D STED within the entire oocyte. O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

Melanin plays a significant role in the regulation of epidermal homeostasis and photoprotection of human skin. The assessment of its epidermal distribution and overall content is of great interest due to its involvement in a wide range of physiological and pathological skin processes. Among several spectroscopic and optical imaging methods that have been reported for non-invasive quantification of melanin in human skin, the approach based on the detection of two-photon excited fluorescence lifetime distinguishes itself by enabling selective detection of melanin with sub-cellular resolution, thus facilitating its quantification while also resolving its depth-profile. A key limitation of prior studies on the melanin assessment based on this approach is their inability to account for the skin heterogeneity due to the reduced field of view of the images, which results in high dispersion of the measurement values. Pigmentation in both normal and pathological human skin is highly heterogeneous and its macroscopic quantification is critical for reliable measurements of the epidermal melanin distribution and for capturing melanin-related sensitive dynamic changes as a response to treatment. In this work, we employ a fast large-area multiphoton exoscope (FLAME), recently developed by our group for clinical skin imaging, that has the ability to evaluate the 3D distribution of epidermal melanin content in vivo macroscopically (millimeter scale) with microscopic resolution (sub-micron) and rapid acquisition rates (minutes). We demonstrate significant enhancement in the reliability of the melanin density and distribution measurements across Fitzpatrick skin types I to V by capturing the intra-subject pigmentation heterogeneity enabled by the large volumetric sampling. We also demonstrate the potential of this approach to provide consistent measurement results when imaging the same skin area at different times. These advances are critical for clinical and research applications related to monitoring pigment modulation as a response to therapies against pigmentary skin disorders, skin aging, as well as skin cancers.

We describe a novel microscopy for studying the network of axons in the unlabeled fresh wholemount retina. The intrinsic radiation of second harmonic generation (SHG) was utilized to visualize single axons of all major retinal neurons, i.e., photoreceptors, horizontal cells, bipolar cells, amacrine cells, and the retinal ganglion cells. The cell types of SHG+ axons were determined using transgenic GFP/YFP mice. New findings were obtained with retinal SHG imaging: Muller cells do not maintain uniformly polarized microtubules in the processes; SHG+ axons of bipolar cells terminate in the inner plexiform layer (IPL) in a subtype-specific manner; a subset of amacrine cells, presumably the axon-bearing types, emits SHG; and the axon-like neurites of amacrine cells provide a cytoskeletal scaffolding for the IPL stratification. To demonstrate the utility, retinal SHG imaging was applied for testing whether the inner retina is preserved in glaucoma, using DBA/2 mice as a model of glaucoma and DBA/2-Gpnmb+ as the non-glaucomatous control. It was found that the morphology of the inner retina was largely intact in glaucoma and the pre-synaptic compartments to the retinal ganglion cells were uncompromised. It proves retinal SHG imaging as a promising technology for studying the physiological and diseased retina in 3D.

This research focuses on the investigation of the propagation of frequencies between 0.1 and 2.5 THz through a phantom ear model using terahertz (THz) time-domain spectroscopy (TDS). While the use of THz frequencies between 0.1 to 0.3 THz in fifth and sixth generation cellular networks has gained significant attention, there is also a growing interest in utilising higher frequencies, such as 1 THz and above, for various applications, including the Internet of Things (IoT), autonomous vehicles, smart sensors, and smart cities. Despite the limited absorption coefficient of soft tissues at 5G and 6G frequencies (0.2-0.4 mm), the effect of higher frequencies on deeper regions of the ear, such as the tympanic membrane (with a thickness of 0.1 mm), has not been extensively studied. The study aims to determine the optimal conditions for THz transmission through the ear canal and to investigate the interaction between wireless networks and biological tissues. The results show that when parallel to the ear canal, the average power flux density within the central region of the tympanic membrane is 97% of the incident excitation. However, the outer ear structures are highly protective, with less than 0.4% of the power flux density directed towards them reaching the same region. Due to the sensitivity of the tympanic membrane to mechanical changes, in-vivo assessments are necessary to evaluate the penetration of THz frequencies into the ear canal, assess the suitability of current radiation safety limits, and evaluate the implications of devices that emit these frequencies. The study highlights the importance of understanding the interaction between THz radiation and biological tissues, particularly in the context of emerging wireless technologies, and the need for further research to ensure their safety and effectiveness.

Micro-optical coherence tomography ({micro}OCT) improves the spatial resolution of in vivo OCT imaging by utilizing sophisticated focusing schemes and broadband illumination. This study explores the safety of coronary and trachea tissue exposure to {micro}OCT illumination. (C) 2021 The Authors

Using a sensitive research-grade infrared camera, we find that common facial cosmetics and lotions mask skin temperature in assays of the human forehead. We test a family of 10 commonly-used cosmetic products and find that volatile liquids and creams lower thermal skin temperature by at least 2 C for up to 5-10 min and at least 1 C for up to 20 min, respectively. Powder and cream that contains brightening agent lower indefinitely the skin temperature sensed by infrared camera. With the qualification that these experiments were performed in a controlled laboratory setting rather than the mass crowd screening environment where infrared temperature sensing of humans sees widespread use, our tests suggest that for human subjects whose face was treated with certain cosmetics and lotions, infrared-based screening for elevated facial temperature (fever) can be unreliable.

Collagen forms dense fibre networks in the human body, with the organisation directly influencing tissue mechanics and function in health and disease. A good understanding of this relation requires proper imaging techniques for visualising the dense collagen network. Previously, computational scattered light imaging was employed as a fast and easy-to-implement technique to retrieve the orientation of multi-directional collagen fibres, but results were not yet validated quantitatively. In this study, we validate the in-plane orientations of collagen fibres determined with computational scattered light imaging by performing comparative measurements with polarimetric second harmonic generation microscopy on rat tendon and bone sections. For rat tendon, sections with and without hematoxylin-and-eosin staining, folded tendon layers, and obliquely cut sections were investigated. Similar fibre orientations were obtained with both techniques in both tissues, with the highest degree of similarity found for in-plane, unidirectional fibres in the tendon sections. The techniques were able to retrieve the orientations of multi-directional crossing collagen fibres in folded rat tendon layers, and results were found to be unaffected by staining. While polarimetric second harmonic generation microscopy provides high resolution and ultrastructural information on collagen, computational scattered light imaging provides large field of view measurements with micrometre resolution.

BackgroundHospital aquired infections is a considerable challenge for vulnerable patients. Ultraviolet light based on the excitation of mercury emit light at 254nm and has well established antimicrobial effects but the use hereof in populated areas is hindered by the carcinogenic properties of 254nm. This is in contrast to the recently developed excimer lamps based on krypton chloride (KrCl). These lamps emit light with a peak intensity at a wavelength of 222nm and have recently been demonstrated to have broad bactericidal and viricidal effects including efficient inactivation of SARS-CoV2. It is, however, unclear how efficiently 222nm lamps perform in a real-life setting such as a hospital waiting area. In this study we aimed to assess the antimicrobial efficacy of filtered 222nm excimer lamps in a real-world setting at an out-patient pulmonology clinic. MethodsFiltered KrCl 222nm excimer lamps (UV222 lamps) were installed in a densely populated waiting room at the out-patient waiting area at Department of Respiratory Diseases and Allergy at Aarhus University Hospital, Aarhus, Denmark. Furniture sufaces were sampled and analyzed for bacterial load in a single arm interventional longitudinal study with and without exposure to filtered 222nm UVC-light. Furthermore, bacterial species were identified using MALDI-ToF mass-spectrometry. FindingsThe exposure to filtered 222nm UVC-light significantly reduced the number of colony-forming-units, and patches with high desity of bacteria. Pathogenic bacteria such as Staphylococcus Aureus and Staphylococcus Epidermidis were detected only in the non-exposed areas suggesting that these species are highly sensitive to inactivation by 222nm UVC-light. ConclusionFiltered 222nm UVC-light is highly anti-microbial in a real-world clinical setting reducing bacterial load and eradicating clinically relevant bacteria species. Filtered 222nm UVC-light has the potential to become an important part of current and future anti-microbial prevention in the clinic.

Polarimetric second harmonic generation (SHG) microscopy is employed to study partially oriented fibrillar structures. The polarimetric SHG parameters are influenced by three-dimensional (3D) configuration of C6 symmetry fibrilar structures in the focal volume (voxel) of a microscope. The achiral and chiral susceptibility tensor components ratios (R and C, respectively) are extracted from the linear polarization-in polarization-out (PIPO) measurements. The analytical derivations along with the polarimetric SHG microscopy results obtained from rat tail tendon, rabbit cornea, pig cartilage and meso-tetra (4-sulfonatophenyl) porphine (TPPS4) cylindrical aggregates demonstrate that SHG intensity is affected by parallel/antiparallel arrangements of the fibers, and R and C ratio values change by tilting the fibers out of image plane, as well as by crossing the fibers in 2D and 3D. The polarimetric microscopy results are consistent with the digital microscopy modeling of fibrillar structures. These results facilitate the interpretation of polarimetric SHG microscopy images in terms of 3D organization of fibrilar structures in each voxel of the samples. Statement of SignificancePolarimetric second harmonic generation (SHG) microscopy is used to study partially oriented C6 symmetry chiral fibrillar structures. The linear polarization-in polarization-out (PIPO) SHG imaging is performed on rat tail tendon, rabbit cornea, pig cartilage tissues and meso-tetra (4-sulfonatophenyl) porphine (TPPS4) cylindrical aggregates. The study demonstrates that SHG intensity is affected by parallel/antiparallel arrangements of the fibers, and the achiral and chiral susceptibility component ratio values change by tilting the fibers out of image plane, as well as by crossing the fibers in 2D and 3D. The polarimetric microscopy results are consistent with the digital microscopy modeling of fibrillar structures. These results facilitate the interpretation of polarimetric SHG microscopy images in terms of 3D organization of fibrillar structures in each voxel of the samples.

BACKGROUNDThe mammalian skin, the bodys largest single organ, is a highly organized tissue that forms an essential barrier against dehydration, pathogens, light and mechanical injury. Damage triggers perturbations of the cytosolic free Ca2+ concentration ([Ca2+]c) that spread from cell to cell (known as intercellular Ca2+ waves) in different epithelia, including epidermis. Ca2+ waves are considered a fundamental mechanism for coordinating multicellular responses, however the mechanisms underlying their propagation in the damaged epidermis are incompletely understood. AIM OF THE PROJECTTo dissect the molecular components contributing to Ca2+ wave propagation in murine model of epidermal photodamage. METHODSTo trigger Ca2+ waves, we used intense and focused pulsed laser radiation and targeted a single keratinocyte of the epidermal basal layer in the earlobe skin of live anesthetized mice. To track photodamage-evoked Ca2+ waves, we performed intravital multiphoton microscopy in transgenic mice with ubiquitous expression of the sensitive and selective Ca2+ biosensor GCaMP6s. To dissect the molecular components contributing to Ca2+ wave propagation, we performed in vivo pharmacological interference experiments by intradermal microinjection of different drugs. EXPERIMENTAL RESULTSThe major effects of drugs that interfere with degradation of extracellular ATP or P2 purinoceptors suggest that Ca2+ waves in the photodamaged epidermis are primarily due to release of ATP from the target cell, whose plasma membrane integrity was compromised by laser irradiation. The limited effect of the Connexin 43 (Cx43) selective inhibitor TAT-Gap19 suggests ATP-dependent ATP release though connexin hemichannels (HCs) plays a minor role, affecting Ca2+ wave propagation only at larger distances, where the concentration of ATP released from the photodamaged cell was reduced by the combined effect of passive diffusion and hydrolysis due to the action of ectonucleotidases. The ineffectiveness of probenecid suggests pannexin channels have no role. As GCaMP6s signals in bystander keratinocytes were augmented by exposure to the Ca2+ chelator EGTA in the extracellular medium, the corresponding transient increments of the [Ca2+]c should be ascribed primarily to Ca2+ release from the ER, downstream of ATP binding to P2Y purinoceptors, with Ca2+ entry through plasma membrane channels playing a comparatively negligible role. The effect of thapsigargin (a well-known inhibitor of SERCA pumps) and carbenoxolone (a recently recognized inhibitor of Ca2+ release through IP3 receptors) support this conclusion. CONCLUSIONSThe one presented here is an experimental model for accidental skin injury that may also shed light on the widespread medical practice of laser skin resurfacing, used to treat a range of pathologies from photodamage and acne scars to hidradenitis suppurativa and posttraumatic scarring from basal cell carcinoma excision. The results of our experiments support the notion that Ca2+ waves reflect chiefly the sequential activation of bystander keratinocytes by the ATP released through the compromised plasma membrane of the cell hit by laser radiation. We attributed the observed increments of the [Ca2+]c chiefly to signal transduction through purinergic P2Y receptors. Several studies have highlighted fundamental roles of P2Y receptors during inflammatory and infectious diseases, and the initial phase of wound healing involves acute inflammation. In addition, hyaluronan is a major component of the extracellular matrix and its synthesis is rapidly upregulated after tissue wounding via P2Y receptor activation. It is tempting to speculate that response coordination after injury in the epidermis occurs via propagation of the ATP-dependent intercellular Ca2+ waves described in this work.