title: Activation of electrogenic Na+/K+ exchange by extracellular K+ in canine cardiac Purkinje fibers.
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.
mesh_terms: D000818:Animals; D004285:Dogs; D004553:Electric Conductivity; D004789:Enzyme Activation; D005110:Extracellular Space / Q000378:metabolism; D006329:Heart Conduction System / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D011188:Potassium / Q000378:metabolism*; D011690:Purkinje Fibers / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium