A role for cGMP during tetanus toxin blockade of acetylcholine release in the rat pheochromocytoma (PC12) cell line.

In order to identify the specific molecular mechanisms involved in neurosecretion, we investigated the mechanism of action of tetanus toxin, a potent presynaptic neurotoxin, in the rat adrenal pheochromocytoma PC12 cell line. It has recently been reported that tetanus toxin is a potent inhibitor of the release of depolarization-evoked 3H-acetylcholine (ACh) from nerve growth factor-differentiated PC12 cells (Sandberg et al., 1989a). In PC12 cells, as in many neural tissue preparations, cGMP accumulation in intact cells increased 6- to 17-fold when stimulated with veratridine (200 microM), carbachol (1 mM), Ba2+ (2 mM), or K+ (30 mM). Preincubation of the cells with tetanus toxin inhibits this accumulation by greater than 95%. The toxin dose-inhibition curves for 3H-ACh release and cGMP accumulation are similar, with half-maximal doses of tetanus toxin seen at approximately 5 nM. The time courses for the development of the effects of tetanus on 3H-ACh release and on cGMP accumulation were also similar. Protocols which elevated intracellular cGMP levels reversed the action of the toxin. For example, evoked ACh release was restored in intoxicated PC12 cells by a 15 min exposure to 100 microM 8-bromo-cGMP. The half-maximal dose was observed at 50 microM nucleotide. Examination of the nucleotide specificity revealed that only cyclic guanine analogs were effective in reversing the effects of tetanus toxin. These results suggested that the inhibition of depolarization-evoked cGMP accumulation is causally related to the action of tetanus toxin on neurosecretion.(ABSTRACT TRUNCATED AT 250 WORDS)