Binding of Radioactive Sodium, Potassium, and Bromide in Guinea Pig Brain Homogenates.

Summary 1. Dialysis of guinea pig brain homogenates from animals given intraperitoneal injections of radioactive tracers revealed that 3%-4% of brain sodium (1.7 mEq/kg wet brain), bromide and potassium (3.5 mEq/kg) were “bound”, i.e., did not pass the dialysis membrane. 2. Centrifugation studies indicated that these “bound” fractions were contained in the sedimentable portion of the homogenates, and therefore are not mitochondrial or microsomal, as these terms are usually defined. 3. Similarities in amount and development of “binding” of these 3 elements, and in the effects of centrifugation, as well as the absence of comparable binding in liver suggested that this binding may be related to the presence of myelin. 4. The level of bound sodium decreased 50% as a result of convulsions, with no concomitant change in bromide or potassium. 5. The significance of these observations was discussed.