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

1. Previous work has shown that a frog sartorius muscle consists of parallel cells running all the way from one end of the muscle to the other and that amputation of one end of the muscle is not followed by regeneration of a new cell membrane. If now 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, we have what is described as an effectively membraneless open-ended cell or EMOC preparation. In this case the only remaining anatomically intact plasma membrane and pumps are made nonfunctional by the removal of 'sources' for inward pumps and 'sinks' for outward pumps. 2. The healthy region of a frog sartorius muscle EMOC preparation continues to accumulate labelled K+ to a level higher than that in the Ringer solution and to exclude labelled 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. 3. The diffusion coefficient of Na+ in the normal muscle cytoplasm at 25 degrees C was measured using two methods. The average diffusion coefficient measured was 2.07 X 10(-6) cm2/sec, roughly 1/6 that of the diffusion coefficient of Na+ in a 0.1 N-NaCl solution. 4. The data obtained are discussed in terms of the association-induction hypothesis. In this theory asymmetrical solute distribution, basically an expression of a non-energy consuming metastable equilibrium state, is the result of specific combinations of two opposing mechanisms: adsorption which raises the level of the intracellular solute; and exclusion from cell water which tends to lower it.