Contribution of an electrogenic sodium pump to membrane potential in mammalian skeletal muscle fibres.

Abstract

SUMMARY1. Relationship between the resting membrane potential and the changes in the intracellular Na and K concentrations ([Na]i and [K]1) was studied in 'Na-loaded' and 'K-depleted' soleus (SOL) muscles of rats which had fed a K-free diet for 40 and more days.2. The extracellular space of the muscles was not significantly different between normal and K-deficient rats. The inulin space in both the 'fresh' and 'Na-rich' muscles can be determined by the same function relating the space to the muscle weight.3. Presence of 2-5-15 mm-K in the recovery solution hyperpolarized the 'Na-rich' muscle fibres at the beginning of recovery. The hyperpolarized membrane potential exceeded, beyond the measured potential of 'fresh' muscle fibres, the theoretical potential derived from the ionic theory, or even beyond Ek. Then, the measured membrane potential declined progressively during the immersion in a recovery solution and returned to the steady-state value. When a considerable Na extrusion and K uptake took place, the measured membrane potential became equal to Ek. 6. The membrane potential obtained after inhibition of the electrogenic Na-pump with cooling or ouabain agrees well with that predicted by the 'constant-field' equation.7. The external Cl ions had a short-circuiting effect on the electrogenic Na-pumping activated on adding K ions.22-2 8. The replacement of Na ions in a recovery solution with Li ions resulted in a faster rate of depolarization from the maximal hyperpolarization.9. It is concluded that the resting membrane potential of 'Na-loaded' and 'K-depleted' SOL muscle fibres is the sum of an ionic diffusion potential predicted by either the Nernst equation or the constant-field equation and of the potential produced by an electrogenic Na-pump.

The electrogenic Na‐pump and spontaneous contraction of the hypokalemic rat duodenum

“…In other experiments, we found that increasing the K4 concentration in the recovery Krebs solution led to a hyperpolarization of 'Na-rich' skeletal muscle fibres from hypokalemic rats which appeared earlier and the duration of which was shortened with increasing concentration (Akaike, 1975a). The peak post-tetanic hyperpolarization of non-myelinated nerve fibres of the rabbit was also found to decline significantly at a [Kb.…”

“…At the start of expenments, rats were stunned and bled, the duodenum (2 cm caudal to the pylorus) was isolated and emptied of contents by flushing with 0.9% saline, and longitudinal segments (1 cm) were prepared. (Desmedt, 1953;Akaike, 1975a).…”

“…ouabain (Akaike, 1974;1975a). However, the contribution of the electrogenic Na-pump to contractile activities of 'Na-rich' smooth muscles isolated from hypokalemic rats has remained unknown.…”

“…At the start of the recovery, the 'Na-rich' skeletal muscle fibres were hyperpolarized (Akaike, 1974;1975a;1976;198 1). The period of hyperpolarization was shortened with increasing levels of [K]O.…”

Ionic basis of resting membrane potential in frog taste cells.

“…Partial non-linearity between eV FART and [K+]o like that in Fig. 6 has been found in molluscan neurons by MARMOR (1970, 1974) and in skeletal muscle fibers by AKAIKE (1975). Deviation from a straight line occurs around K+ concentration in the normal saline solution.…”