Inhibition of sodium pump by l-palmitoylcarnitine in single guinea-pig ventricular myocytes.
We reinvestigated the issue of whether l-palmitoylcarnitine inhibits the Na/K pump in the heart. The effects of l-palmitoylcarnitine or ouabain on the Na/K pump current were studied with the voltage-clamp technique in isolated guinea-pig ventricular myocytes. In myocytes bathed in Tyrode's solution, l-palmitoylcarnitine shifted the current-voltage relation inward at all potentials between -80 and 20 mV. the "U"-shaped difference current seen in l-palmitoylcarnitine was maximal at -30 mV and declined at potentials more positive and negative than this. Under conditions that minimized time-dependent currents, ouabain or l-palmitoylcarnitine shifted membrane current inward in the presence of 5.4 mM extracellular potassium. Reduction of extracellular potassium to 0 mM for 2 min also shifted membrane current inward. When extracellular potassium was returned to 5.4 mM, the intracellular sodium that had accumulated was extruded and a transient outward current was generated as a result of Na/K pump stimulation. Ouabain or l-palmitoylcarnitine reversibly suppressed this transient outward current and reduced the rate constant for the decline of this current. The ability of l-palmitoylcarnitine to imitate the actions of ouabain on membrane current and on the transient outward current indicates that this amphiphile inhibits the Na/K pump current in guinea-pig ventricular myocytes. This results is consistent with the suppression by l-palmitoylcarnitine of the activity of Na/K ATPase in cardiac sarcolemmal vesicles.
Tanaka
M
M
Department of Physiology, Showa University School of Medicine, Tokyo, Japan.
Gilbert
J
J
Pappano
A J
AJ
D000818:Animals; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000502:physiology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D010172:Palmitoylcarnitine / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000502:physiology*; D016276:Ventricular Function
D010172:Palmitoylcarnitine; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase