Maintenance of low sodium and high potassium levels in resting muscle cells.

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Abstract
A frog sartorius muscle consists of parallel cells running all the way from 1 end of the muscle to the other, and amputation of 1 end of the muscle was not followed by regeneration of a new cell membrane. If only the cut end of the amputated muscle is exposed to a Ringer solution, in which the solutes 42K and 22Na act as radioactive labels, and the rest of the cell is suspended in air, an effectively membraneless open-ended cell (EMOC) preparation may be studied. In this case the only remaining anatomically intact plasma membrane and pumps were made nonfunctional by the removal of sources for inward pumps and sinks for outward pumps. The healthy region of a frog sartorius muscle EMOC preparation continued to accumulate labeled K+ to a level higher than that in the Ringer solution and to exclude labeled Na+ to a level below that in the Ringer solution, much as a normal uncut muscle does in its normal environment. The differences were reduced by inclusion of ouabain in the medium. The diffusion coefficient of Na+ in the normal muscle cytoplasm at 25.degree. C was measured using 2 methods. The average diffusion coefficient measured was 2.07 .times. 10-6 cm2/s, roughly 1/6 that of the diffusion coefficient of Na+ in a 0.1 N-NaCl solution. The association-induction hypothesis was discussed. In this theory asymmetrical solute distribution, basically an expression of a non-energy consuming metastable equilibrium state, was the result of specific combinations of 2 opposing mechanisms: adsorption which raises the level of the intracellular solute; and exclusion from cell water which tends to lower it.