Sodium dependency of γ-aminobutyric acid binding to particulate fractions of mouse brain

Abstract

The Na +-dependency of γ-aminobutyric acid (GABA) binding to particulate fractions of mouse brain was studied, by increasing the concentration of Na + in the homogenizing fluid the retention of both [ 3H] GABA and [ 14C] sucrose was increased in the crude nuclear fractions. But, at Na + concentrations greater than 10 meq/l, the retention of both substances was decreased in the synaptosomal-mitochondrial fractions. Although the total [ 3H] GABA bound to all fractions was increased by increasing the Na + concentration of the homogenizing medium, the total [ 14C] sucrose entrapped in these fractions remained rather constant. The changes in GABA binding caused by Na + thus could not be accounted for by the presence of entrapped homogenizing fluid in pellets. The decreased binding of GABA to synaptosome fractions found in the presence of 40 to 100 meq/l Na + was due to “clumping” effects caused by the excess salt. With high salt concentrations many of the particles which bind GABA and which are normally associated with the synaptosome fraction were sedimented in the crude nuclear fraction. In sum, these results indicated that the binding of GABA occurs maximally at a Na + concentration of about 40 meq/l.