Depolarizing agents and cyclic nucleotides regulate the phosphorylation of specific neuronal proteins in rat cerebral cortex slices.

Abstract

The regulation of the state of phosphorylation of 2 specific neuronal proteins, designated protein Ia and protein Ib, was studied in slices of rat cerebral cortex incubated in vitro. For this purpose, a method was developed that prevented dephosphorylation of these proteins during their extraction. When the slices were incubated in a standard Krebs-Ringer solution, proteins Ia and Ib were present almost entirely in the dephosphorylated form. Incubation with cyclic[c]AMP, 8-bromo cAMP, N6-monobutyryl cAMP or with a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, increased the phosphorylation of proteins Ia and Ib in the slices. Depolarization of neuronal membranes by high K+ or by veratridine was also associated with an increased phosphorylation of proteins Ia and Ib. The effect of depolarizing agents, but not that of cyclic nucleotides or 3-isobutyl-1-methylxanthine, required the presence of external Ca2+ in the incubation medium. Tetrodotoxin blocked the stimulation of the phosphorylation of proteins Ia and Ib induced by veratridine but not that induced by the other agents tested. Incubation of the brain slices with 8-bromo cAMP, 3-isobutyl-1-methylxanthine, high K+ or veratridine also increased the state of phosphorylation of 2 other neuronal proteins found in extracts of the slices.