EFFECTS OF SOMATOSTATIN ON INTRACELLULAR CALCIUM-CONCENTRATION IN PC12 CELLS

Somatostatin (SS) is a neuropeptide that is distributed in various reg ions of the CNS, where it may act as a neurotransmitter or neuromodula tor. SS produces multiple effects in the CNS through interactions with membrane receptors. In particular, SS inhibits various secretory resp onses in different cell types. In the present study, we have investiga ted the effects of exogenous application of SS on the intracellular fr ee Ca2+ concentration ([Ca2+](i)) in PC12 cells, a rat pheochromocytom a cell line. SS did reduce the magnitude of the secondary, maintained Ca2+ influx brought about by K+ depolarization. Similar effects were o btained with the application of SS analogues, such as D-Trp(8)-SS, D-T rp(8)-D-Cys(14)-SS, CGP-23996, and SMS-201995. In addition, treatment with cyclo-SS, a SS antagonist, did not alter [Ca2+](i). Experiments w ith selective blockers of different voltage-dependent Ca2+ channels, s uch as methoxyverapamil (D600) and Omega-conotoxin GVIA, demonstrated that the effects of SS on [Ca2+](i) were mediated by voltage-dependent Ca2+ channels of the L type. Control experiments with a membrane pote ntial indicator, i.e., the fluorescent dye bisoxonol, excluded that SS influenced the level of the membrane potential. SS effects on PC12 ce lls suggest the possibility that this neuropeptide plays a role in the modulation of cell functional activity by altering Ca2+ influx.