Voltage dependence of transient and steady-state Na/K pump currents in myocytes.
Experiments are reviewed here in which Na/K pump current was determined as strophanthidin-sensitive current in guinea-pig ventricular myocytes, voltage-clamped and internally-dialyzed via wide-tipped pipettes. In the presence of 150 mM extracellular [Na], both outward and inward pump current, during forward and reverse Na/K exchange respectively, were strongly voltage dependent. But reduction of external [Na] to 1.5 mM severely attenuated the voltage sensitivity of outward Na/K pump current. Voltage jumps elicited large transient pump currents during forward or reverse Na/K exchange, or when pump activity was restricted to Na translocation steps, but not when pumps were presumably engaged in K/K exchange. These findings indicate that Na translocation, but not K translocation, involves net charge movement through the membrane field, and that both forward and reverse Na/K transport cycles are rate-limited not by that voltage-sensitive step but by a subsequent voltage-insensitive step.
Gadsby
D C
DC
Laboratory of Cardiac Physiology, Rockefeller University, New York, New York 10021.
Nakao
M
M
Bahinski
A
A
D000818:Animals; D001693:Biological Transport, Active; D004558:Electric Stimulation; D006168:Guinea Pigs; D007474:Ion Exchange; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013327:Strophanthidin / Q000494:pharmacology
D013327:Strophanthidin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium