Possible role of calcium-dependent protein phosphorylation in mediating neurotransmitter release and anticonvulsant action.

The results demonstrate that calcium and phenytoin have antagonistic actions on the net level of endogenous phosphorylation of specific rat brain proteins. These specific phosphoproteins were shown to be present in synaptosome preparations, and evidence is presented for the localization of these phosphoproteins within the presynaptic nerve terminal. The data are compatible with the hypothesis that the antagonistic actions of calcium and phenytoin on the phosphorylation of synaptosome proteins may be the underlying molecular mechanism mediating the opposing actions of these agents on the release of neurotransmitter from the presynaptic nerve terminal.