1) Changes in the membrane potential of sodium-loaded frog'sskeletal muscle caused by a sudden rise of temperature (thermohyperpolarization) were observed with or without ouabain at different membranepotential levels by applying different anodal or cathodal currents.
2) The membrane was hyperpolarized when the applied current wasabsent. The amplitude of the thermohyperpolarization was decreasedwhen the original membrane potential level at low temperature (2°C) was hyperpolarized. The thermohyperpolarization finally disappeared ata certain level (the thermoreversal potential) and reversed its polaritywhen the membrane was hyperpolarized beyond this level.
3) The changes in the membrane conductances at different potentiallevels were also measured with and without 10
-5 M ouabain. The membraneconductance and potential were unchanged at low temperatureirrespective of the presence of ouabain. The membrane conductanceincreased with the rise of temperature and the presence of ouabaincaused the decrease in the membrane conductance at the high temperature (26°C). The current-voltage relationships were constructed fromconductance data.
4) The current required for compensating the thermohyperpolarization (the compensating current) was also measured. The compensatingcurrent as well as the thermohyperpolarization was consistently explainedin terms of the current-voltage relationships.
5) Assuming that ouabain supresses only the pump, the pump potentialdrop and the pump current were calculated as the difference betweenthe thermohyperpolarizations with and without ouabain and that betweencompensating currents with and without ouabain, respectively.Analysis of these data suggested the existence of the pump equilibriumpotential.
6) The thermohyperpolarization, the thermoreversal potential and thepump equilibrium potential were dependent on the external potassiumconcentration having a maximum near 3.5mm and decreased by eitherincreasing or decreasing the potassium concentration.
7) The equivalent electrical circuit for the sodium-loaded frog's skeletalmuscle was proposed.
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