Study of the relationship between sodium ion and hydrogen ion regulation in rat skeletal muscle

The purpose of this study was to elucidate the relationship between the active transport of sodium and the regulation of intracellular pH in rat skeletal muscle. Experiments were conducted both in vivo and in vitro in which Na transport and tissue acid-base balance changed independently and concurrently. Ouabain was employed to inhibit the Na transport system. The ability of cell to maintain a constant internal pH was challenged by producing graded intensities of extracellular metabolic and respiratory acidosis. Acidosis alone had no discernible effect on the sodium transport system in in-vivo experiments. No correlation could be demonstrated between intracellular Na+ and either intracellular or extracellular H+, nor was the electrochemical gradient for sodium affected by acidosis in vivo. The electrochemical gradient for sodium was increased by acidosis in vitro, however, suggesting a stimulation of the Na pump by H. Does of ouabain which caused a marked impairment of sodium transport resulting in an accumulation of Na in skeletal muscle did not cause a parallel accumulation of H in in-vivo experiments except in the most severely acidotic animals. In the in-vitro experiments, ouabain did an intracellular acidosis in tissues subjects to acid challenges. Several factors might explain the failure of ouabain to alter cell pH to any significant degree in the in-vivo experiments, even though the drug may have impaired the proposed Na-H transport system. First, the large increase in plasma K which invariably accompanied ouabain administration in vivo very probably antagonized the action of ouabain on the Na-H pump. In in-vitro experiments where external potassium did not vary, ouabain was found to impair the ability of skeletal muscle to resist an acid challenge and under these conditions did cause an accumulation of H+ intracellularly. Second, acidosis per se may have stimulated the pump sufficiently to antagonize the inhibitory influence of oubain of H transport. Third, there was some evidence that the intracellular HCO3 concentration was higher in ouabain-treated animals, possibly because the electrochemical gradient which ordinarily drives this ion out of the cell was reduced. This would mean that even though less H might be extruded in the ouabain-treated animals, the excel H would be buffered by HCO3. Finally, the possibility was considered that a change in cell pH may not be a vailid criterion for determining the impairment of H transport, and that a change in the electrochemical gradient for H may be a better standard for evaluating changes in H distribution. It was clear that ouabain does reduce the electrochemical gradient for H both in vivo and in vitro. The results of these experiments are thus consistent with the hypotheses that 1) H is actively transported out of skeletal muscle cells, and 2) the mechanism responsible for the active extrusion of H is extremely similar to, or perhaps even identical with, the mechanism underlying the active extrusion of Na in skeletal muscle.