The purpose of this project is to characterize second messenger pathways involved in receptor regulation of neurotransmitter levels. Previous work from our lab demonstrated that angiotensin II (AII) and nicotine each stimulate enkephalin secretion and gene expression in cultured bovine chromaffin cells. Both agonists increase intracellular CA2+ concentration (Cai) and protein kinase C (PKC) translocation through different mechanisms of action. Nicotine activates cation channels, L-type Ca2+ channels in particular being important for both Cai and PKC responses; the latter response in long-lived and may contribute to enkephalin gene regulation. Cultured brain cells show PKC responses to cation channel-linked receptors--NMDA, kainate and AMPA--and to PLC-linked receptor agonists--tACPD and dopamine and norepinephrine. Agonists which increase Ca2+ influx into brain cells also produce long-lasting increases in PKC activation in all brain cell cultures examined. Depolarization with high extracellular K+ also increases PKC long-term in these cells but only increases enkephalin biosynthesis in olfactory bulb cell cultures and not in striatal, hippocampal or hypothalamic cell cultures. cAMP and PKC pathways effectively increase enkephalin biosynthesis in all brain cell cultures examined. Tyrosine hydroxylase levels are increased in olfactory bulb cultures by each pathway which stimulates enkephalin biosynthesis except K+ depolarization, and the basis for this difference is being examined.
