Synaptic transmission and neurosecretion have been reported to be altered by ethanol; however, the mechanisms involved in these effects are poorly understood. We studied neurosecretory mechanisms and the actions of ethanol on those mechanisms in the ACTH secreting mouse pituitary cell line, AtT-20, and the catecholamine secreting rat chromaffin cell line, PC12. We found that somatostatin inhibits the voltage-dependent calcium current in AtT-20 cells. Pertussis toxin comletely abolished the action of somatostatin on calcium current. Intracellular application of GTP-gamma-S rendered irreversible the somatostatin-induced inhibition of calcium current. The results indicate that the somatostatin receptor is coupled to a GTP-binding protein which mediates inhibition of voltage-dependent calcium channels. PC12 cells were used to examine the effect of muscarinic receptor stimulation on inositol trisphosphate, intracellular calcium and catecholamine release. When PC12 cells were exposed to muscarine the cells rapidly respond with elevation of cellular inositol trisphosphate, elevation of intracellular calcium and release of transmitter. These three phenomena displayed similar time courses and concentration-dependencies. The increase in intracellular calcium appeared to be due to a mobilization of calcium from intracellular stores. The results suggest that muscarine-stimulated release of neurotransmitter may be associated with an inositol trisphosphate-induced mobilization of intracellular calcium. The effects of ethanol are being tested on these secretory mechanisms. The significance of the project derives from the fact that characterization of neurosecretory mechanisms and the actions of ethanol on those mechanisms should increase our understanding of the cellular basis of ethanol's actions in the nervous and endocrine systems.
