Is potassium co-transported by the cardiac Na-Ca exchange?
It has been suggested that the stoichiometry of the electrogenic Na-Ca exchange is 3Na:1Ca. Recently, however, it was reported in rod outer segments that the stoichiometry of Na-Ca exchange is not 3Na:1Ca but 4Na:1Ca + 1K. In cardiac cells, the reversal potential has always been measured in the absence of K or at a very low K concentration. We have, therefore, re-examined the reversal potential of the Na-Ca exchange current by whole-cell voltage clamp in single guinea-pig ventricular cells in the presence of K on both sides of the membrane. The Na-Ca exchange current reversed at potentials close to the calculated values for 3Na:1Ca stoichiometry even in the presence of K. The magnitude of the Na-Ca exchange current did not change in 1 and 10 mM [K]o. We therefore conclude that K is not co-transported by cardiac Na-Ca exchange and its stoichiometry is 3Na:1Ca.
Yasui
K
K
National Institute for Physiological Sciences, Okazaki, Japan.
Kimura
J
J
D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics*; D004594:Electrophysiology; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000493:pharmacokinetics*; D012964:Sodium / Q000493:pharmacokinetics*
D012964:Sodium; D011188:Potassium; D002118:Calcium