Key result
In guinea-pig ventricular muscles, resting sodium pump current in normally polarized muscle is approximately 0.16 microA/cm2, which is five times smaller than previously estimated.
The resting sodium pump current in normally polarized guinea-pig ventricular muscle is approximately 0.16 microA/cm2, which is five times smaller than previously estimated.
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.
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Kasamaki et al. (1999) studied Guinea-pig ventricular muscles and myocytes. Cs+ addition vs. Rb+, K+, Li+ was evaluated on Pump potential (hyperpolarization) and pump current. In guinea-pig ventricular muscles, resting sodium pump current in normally polarized muscle is approximately 0.16 microA/cm2, which is five times smaller than previously estimated.
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