SPECIFIC INTRACELLULAR BINDING OF RUBIDIUM BY RAT DIAPHRAGM MUSCLE

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Abstract
Further evidence is presented that the cytoplasm of rat diaphragm muscle exhibits properties of selective ion binding. The preparation of the usual hemidiaphragm involves cutting each muscle fiber of the diaphragm at 2 ends. Associated with this, a characteristic permeability feature of the cell is markedly altered, so that ions which are excluded from intact fibers readily penetrate into the cut fibers of the hemidiaphragm preparation. Under these conditions Na+ and Rb+ both enter the cell water of the cut fibers, but only the latter ion is accumulated against an apparent concentration gradient. The accumulation system for rubidium, which appears to operate with potassium as well, probably cannot be explained in terms of a membrane-pump mechanism. If the present findings on rat diaphragm muscle and the previous findings on Neurospora crassa, which indicate that most of the intracellular potassium may be selectively bound by a cytoplasmic system, should prove applicable to cells generally, certain widely accepted views concerning the role of the membrane in permeability processes may require basic revision.

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