Saturable, sodium-induced release of potassium in the muscle exposed to glycerol.

Investigating the kinetics of K+ efflux, two K+ fractions were found in the muscle exposed to 5.8 M glycerol solution at -12 degrees C. The minor K+ fraction was exchangeable with Na+. The amount of released K+ ions being in the K+/Na+ ion exchange was saturable with increase in the concentration of Na+ ion in the medium. It was 11 mmol K+/kg wet wt., which corresponds to the magnitude of the "medium" K+ fraction found by A. S. Troshin in the muscle by means of isotope technique. The minor K+ fraction was temperature and ouabain dependent. K+ fraction with similar features was found by W. Negendank in human lymphocytes, however, its magnitude was 120 mmol K+/kg w.wt. The ratio of the two magnitudes is equal to the ratio of the total cell surface of the muscle and the lymphocyte of one kg. From this fact, it can be concluded that the 11 mmol K+/kg fraction exchangeable with Na+ is bound directly to the cell membrane or to an unidentified structure near to the membrane surface. The preference of K+ binding at higher temperature is interpreted by the assumption that both K+ and Na+ bind to the binding sites of the 11 mmol/kg fraction with their hydration shells.