Potassium accumulation in muscle: a test of the binding hypothesis.

Living frog skeletal muscle can accumulate potassium in vitro to concentrations up to 580 millimolar. Both the amount of potassium accumulated and the relationship between intracellular and extracellular potassium concentrations indicate that potassium is "free" under all conditions, rather than bound to cellular macromolecules. The data also indicate that at most 20 percent of the cell water is "bound" in the sense that it excludes electrolytes.