Effects of a sedative and a convulsant barbiturate on synaptosomal calcium transport

In vitro additon of pentobarbital inhibited the synaptosomal accumulation of calcium stimulated by potassium depolarization. This inhibition was not due to changes in membrane potentials nor to an enhancement of sodium-calcium exchange, but was at least partly due to an enhanced efflux of calcium. In contrast, 5-(2-cyclohexylidene ethyl)-5-ethyl barbituric acid, a convulsant barbiturate, did not alter calcium efflux. Glutamate stimulated synaptosomal calcium accumulation by a depolarization-independent process that was insensitive to the effects of pentobarbital. These results suggest that sedative barbiturates stimulate the efflux of calcium from synaptosomes but convulsant barbiturates do not. In addition, there may be a subpopulation of synaptosomes that contains glutamate-activated calcium channels and is insensitive to pentobarbital.