ION BINDING IN MUSCLE HOMOGENATES

Abstract

The sedimentable fraction of a frog muscle homogenate was shown to contain a slight excess of Na as compared to K. Both Na and K associated with the sedimentable material were displaced by NH4NO3 added to the whole homogenate, relatively more K being displaced than Na. CaCl2 and especially MgCl2 were more effective than NH4NO3 in displacing K and Na. Displacement by MgCl2 appeared equally marked for both Na and K. No evidence was found by centrifuged separation of components of a frog muscle homogenate for K binding. Dialysis expts. likewise gave no evidence for K binding, providing that the ion binding of the dialyzing membrane was taken into account. The results are interpreted as evidence for the binding of a small (2-3% of the total) amt. of Na. Possibilities that this bound Na serves as an exchange and transport system at the muscle fiber surface are discussed.