Activation of electrogenic Na+/K+ exchange by extracellular K+ in canine cardiac Purkinje fibers. |
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| Authors: | D C Gadsby |
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| Abstract: | Transient increments in sodium pump current were elicited in small voltage-clamped Purkinje fibers suspended in a fast flow system by briefly exposing them to K+-free fluid, to temporarily inhibit the pump, and then suddenly returning them to K+-containing fluid. The exponential time course of decay of the current increment provides a measure of the pump rate constant for Na+ extrusion. The dependence of that rate constant, and of the peak amplitude of the increment in pump current, on the extracellular K+ concentration was determined. The results indicate: that in cardiac Purkinje cells, as in many other cells, the pump is half-maximally activated by about 1 mM K+; that the coupling ratio for Na+/K+ exchange is independent of either intracellular Na+ concentration or external K+ concentration; and that a simple model in which intracellular Na+ concentration is determined by a passive "leak," and an active extrusion of Na+, seems sufficient to account for moderate changes in cellular Na+ concentration. |
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