Calcium-dependent protein phosphorylation and dephosphorylation in intact brain neurons in culture

Preincubation of intact fetal rat brain neurons in culture with 32Pi results in the incorporation of 32Pi into about 20 specific proteins. Upon stimulation by electrical field stimulation or by K+-induced depolarization, highly significant calcium-dependent increase in phosphorylation of a protein of app. Mr 43 000 and decrease in phosphorylation of an app. Mr 55 000 protein occur. These changes can be attributed to the entry of Ca2+ into the cellular cytoplasm since they can occur upon selective permeabilization of the cell membrane to Ca2+ by the Ca2+-ionophore A23187 and are not observed upon stimulation of the cells in the presence of the Ca2+ channel blocker D-600. These data suggest that these phosphoproteins may be involved in the regulation of processes underlying neurotransmitter release.