Sodium-pump potentials and currents in guinea-pig ventricular muscles and myocytes.
When guinea-pig papillary muscles were depolarized to ca. -30 mV by superfusion with K+-free Tyrode's solution supplemented with Ba2+, Ni2+, and D600, addition of Cs+ transiently hyperpolarized the membrane in a reproducible manner. The size of the hyperpolarization (pump potential) depended on the duration of the preceding K+-free exposure; peak amplitudes (Epmax) elicited by 10 mM Cs+ after 5-, 10-, and 15-min K+-free exposures were 12.9, 17.7, and 23.2 mV, respectively. Pump potentials were unaffected by external Cl- but suppressed by cardiac glycosides, hyperosmotic conditions, and low-Na+ solution. Using Epmax as an indicator of Na+ pump activation, the half-maximal concentration for activation by Cs+ was 12-16.3 mM. At 6 mM, Cs+ was three times less potent than Rb+ or K+ and five times more potent than Li+. From these findings, and correlative voltage-clamp data from myocytes, we calculate that (i) a pump current of 7.8 nA/cm2 generates an Epmax of 1 mV and (ii) resting pump current in normally polarized muscle (approximately 0.16 microA/cm2) is five times smaller than previously estimated.
Kasamaki
Y
Y
Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada.
Guo
A C
AC
Shuba
L M
LM
Ogura
T
T
McDonald
T F
TF
D000818:Animals; D002586:Cesium / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D008297:Male; D008564:Membrane Potentials; D010042:Ouabain / Q000494:pharmacology; D010210:Papillary Muscles / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*; D013327:Strophanthidin / Q000494:pharmacology
D002712:Chlorides; D002586:Cesium; D010042:Ouabain; D013327:Strophanthidin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium