Intrinsic sodium regulation by Na,K-ATPase: The blue crab's salinity adaptation described by a single negative feedback loop

AbstractThe term enantiostasis was introduced by Mangum and Towle to describe functional relationships between environmental changes and an organisms adaptation to them, and furthermore, to distinguish this kind of adaptation from homeostatic control. The defining example of enantiostasis is the blue crabs blood salinity response when exposed to different environmental salinities during the organisms move between the ocean and upriver fresh-water conditions. In this paper an internal negative feedback loop in the Albers-Post mechanism of the sodium pump (Na,K-ATPase, NKA) is used to describe the blue crabs salinity adaptations. The following assumptions are made: Internal sodium ion activates NKA, while external sodium ion inhibits it. To describe the pumps behavior on changed environmental salinities, integral control is implemented by assuming that the activated pump is deactivated by zero-order or close to zero-order kinetics. As a result, internal sodium ion is robustly regulated by the feedbacks environmentally changing setpoint. Enantiostasis and the closely related concept of rheostasis were both introduced to distinguish them from homeostatic mechanisms. However, the here presented results suggest that enantiostasis and the related rheostatic setpoint changes can be viewed as the emergence from a single homeostatic feedback regulation. In addition, the here suggested intrinsic negative feedback of NKA may be present in other Albers-Post based pumps and may also there contribute to homeostatic regulation. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=85 SRC="FIGDIR/small/698424v1_ufig1.gif" ALT="Figure 1"> View larger version (16K): org.highwire.dtl.DTLVardef@1de0d8dorg.highwire.dtl.DTLVardef@14bc8d7org.highwire.dtl.DTLVardef@6ebdc5org.highwire.dtl.DTLVardef@6ce332_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIThe salt adaptation of the blue crab has been investigated based on an internal negative feedback by the sodium pump. C_LIO_LIWhile the salt adaptation of the blue crab has been a defining example of enantiostasis the present results indicate that the blue crabs salt adaptation is a homeostatic property based on an internal feedback in the pumps Albers-Post mechanism. C_LIO_LIThe results further suggest that other pumps based on the Albers-Post mechanism may contain similar negative feedbacks and thereby contribute to homeostatic regulation. C_LI