ENHANCEMENT OF DEPOLARIZATION-DEPENDENT NEUROSECRETION FROM PC12-CELLS BY FORSKOLIN-INDUCED ELEVATION OF CYCLIC-AMP

Abstract

The effects of elevated intracellular cAMP on the release of neurotransmitters was studied using the clonal rat pheochromocytoma cell line, PC12, and forskolin, a direct activator of adenylate cyclase. Intracellular cAMP concentrations ranging from 8-400 times basal levels were achieved with 0.1-100 .mu.M forskolin. Unstimulated release of neurotransmitters was unchanged by any concentration of forskolin. K+-stimulated release of both norepinephrine (NE) and acetylcholine was enhanced by 0.1-10 .mu.M forskolin. Release of NE elicited by depolarization with carbachol and veratridine also was enhanced by 1 .mu.M forskolin. Enhancement of release was reversed by higher concentrations of forskolin, especially in the presence of a phosphodiesterase inhibitor (RO 20-1724 [4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone]) which caused very large increases in cAMP content. The enhancement of transmitter release from the PC12 cells occurred without concomitant changes in agonist-stimulated ion flux through the acetylcholine receptor ion channel, or in depolarization-dependent uptake of 45Ca2+. Increasing the cAMP content of PC12 cells fails to initiate neurosecretion but appears to facilitate some element in the secretion process subsequent to Ca2+ influx.