| Research Abstract |
We have investigated the effects of drugs on catecholamine (CA) secretion from adrenal chromaffin cells, used as a model of catecholaminergic neurons, to clarify the role of Ca^<2+> in secretory mechanism and modulating factors of the intracellular Ca^<2+> effect.
1) ML-9, a perferential inhibitor of myosin ligho-chain kinase (MLCK), inhibited CA secretion stimulated by ACh, high K^+, veratridine or palytoxin by inhibiting Ca^<2+> uptake into the cells, suggesting that MLCK is involved in the secretory mechanism by regulating transmembrane Ca^<2+> uptake. Palytoxin, a potent marine toxin, was found to stimulate CA secretion by activation of Na^+-dependent, TTX insensitive voltage dependent Ca^<2+> channels. Histamine and bradykinin stimulated CA secretion by increasing Ca^<2+> uptake into the cells. Most of the VIP was localized with ACh in the splanchnic nerve terminals and release with ACh and regulated the stimulatory effect of ACh on CA secretion.
2) From the investigation using cytochalasin, vinblastine or actin-like protein, we have proposed the possibility that cytoskeletal elements play an important role in the regulation of tyrosine uptake by the cells, tyrosine hydroxylase (CA synthesis) and CA secretion. The inhibitory effect of flavonoids, Protein kinase C inhibitors, and the stimulatory effect of phorbol ester and Ba^<2+> on CA biosynthesis and secretion suggested the possible involvement of PKC as modulator of secretory mechanism as well as CA biosynthesis.
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