Electrophysiology of the sodium-potassium-ATPase in cardiac cells

Like several other ion transporters, the Na+-K+ pump of animal cells is electrogenic. The pump generates the pump current I-p. Under physiological conditions, I-p is an outward current. It can be measured by electrophysiological methods. These methods permit the study of characteristics of the Na+-K+ pump in its physiological environment, i.e., in the cell membrane. The cell membrane, across which a potential gradient exists, separates the cytosol and extracellular medium, which have distinctly different ionic compositions. The introduction of the patch-clamp techniques and the enzymatic isolation of cells have facilitated the investigation of I-p in single cardiac myocytes. This review summarizes and discusses the results obtained from I-p measurements in isolated cardiac cells. These results offer new exciting insights into the voltage and ionic dependence of the Na+-K+ pump activity, its effect on membrane potential, and its modulation by hormones, transmitters, and drugs. They are fundamental for our current understanding of Na+-K+ pumping in electrically excitable cells.