Depolarization-stimulated protein phosphorylation in pure cholinergic nerve endings.

Cholinergic synaptosomes obtained from the electric organ of Torpedo marmorata have been used to study chemical stimulation-stimulated protein phosphorylation. Cholinergic synaptosomes were exposed to elevated K+0 concentrations or other chemical depolarizing agents such as gramicidin or secretagogues as the calcium ionophore A23187. During depolarization several synaptosomal proteins increase their state of phosphorylation. This phenomenon depends on the presence of Ca2+ in the external medium. These results suggest that stimulation of protein phosphorylation may be implicated in the acetylcholine release process and could represent a modulation mechanism in the neurotransmitter release machinery at this cholinergic synapse.