Orexins are newly discovered neuropeptides regulating feeding and vigilance and have been detected in neuroendocrine cells of the gut. Potential neuroendocrine functions of orexin are unknown. Therefore, the effects of orexin-A on the intestinal neuroendocrine cell line, STC-1. were investigated as a model system. RT-PCR demonstrated the presence of both OX1 and OX2 receptors. Stimulation with orexin-A produced a dose-dependent release of cholecystokinin (CCK), which was abolished by removal of extracellular Ca2+ or the presence of the voltage-gated L-type Ca2+-channel blocker diltiazem (10 muM). Orexin-A (Ox-A) elevated intracellular Ca2+, which was dependent on extracellular Ca2+. Furthermore, orexin-A caused a membrane depolarization in the STC-1 cells. Ox-A neither elevated cAMP levels nor stimulated phosphoinositide turnover in these cells. These data demonstrate a functional orexin receptor in the STC-1 cell line. Ox-A produces CCK release in these cells, by a mechanism involving membrane depolarization and subsequently activation of L-type voltage-gated Ca2+-channels. (C) 2003 Elsevier Inc. All rights reserved.