Activation of Electrogenic Na+/K+Exchange by Extracellular K+in Canine Cardiac Purkinje Fibers

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 77; no. 7; pp. 4035 - 4039
• Main Author: Gadsby, David C.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 01.07.1980; National Acad Sciences
• Subjects: Animals; Biophysics; Canines; Dogs; Electric Conductivity; Electric current; Enzyme Activation; Extracellular Space - metabolism; Heart; Heart Conduction System - metabolism; In Vitro Techniques; Kinetics; Mathematical constants; Membrane potential; Potassium - metabolism; Pumps; Purkinje cells; Purkinje Fibers - metabolism; Sheep; Sodium; Sodium - metabolism; Sodium-Potassium-Exchanging ATPase - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.77.7.4035

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.