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

The regulation of the state of phosphorylation of two specific neuronal proteins, designated protein Ia and protein 1b, has been studied in slices of rat cerebral cortex incubated in vitro. For this purpose, a method was developed that prevents 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 AMP, 8-bromo cyclic AMP, N6-monobutyryl cyclic AMP, 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 cyclic AMP, 3-isobutyl-1-methylxanthine, high K+, or veratridine also increased the state of phosphorylation of two other neuronal proteins found in extracts of the slices.