Regulation of phosphorylation of proteins I, IIIa, and IIIb in rat neurohypophysis in vitro by electrical stimulation and by neuroactive agents.

Abstract

The state of phosphorylation of proteins I, IIIa and IIIb, neuron-specific phosphoproteins, was studied in neurosecretory endings of the neurohypophysis in vitro. Brief periods (a few seconds) of electrical stimulation caused large increases in the state of phosphorylation of all 3 proteins. The 3 proteins were dephosphorylated within 1 min after termination of the stimulation. High K, 8-bromo-cAMP and dopamine also stimulated the phosphorylation of the 3 proteins. The effect of dopamine was blocked by the dopamine antagonist fluphenazine. Peptide mapping of protein I revealed that electrical stimulation or high K increased the state of phosphorylation of 2 regions of the molecule; 8-bromo-cAMP and dopamine increased the state of phosphorylation of only one of these regions.