Serotonin-stimulated increase in cytosolic Ca2+ in cultured rat heart endothelial cells

This study was designed to investigate the effects of serotonin on changes in intracellular Ca2+ concentration ([Ca2+](i)) in cultured rat heart endothelial cells. Serotonin stimulated a biphasic change in cytosolic Ca2+ of rat heart endothelial cells: an initial transient increase, which primarily reflects the release of Ca2+ from internal stores, followed by a slow rise in [Ca2+](i) during the incubation with serotonin. Our study also demonstrated that the pattern of the serotonin-induced increase in [Ca2+](i) was different from that induced by thrombin in rat heart endothelial cells. In this study, the role of [Ca2+](i) on endothelial paracellular barrier function was also investigated. Serotonin induced an increase in endothelial permeability which paralleled the rise in [Ca2+](i) and was blocked by the 5-HT2 receptor antagonist cyproheptadine. Therefore, the serotonin-stimulated increase in cytosolic Ca2+ and macromolecular permeability was receptor-mediated in rat heart endothelial cells. Further experiments demonstrated that the serotonin-induced increase in [Ca2+](i) was inhibited by the phospholipase C inhibitors, neomycin and [6-[[17 beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U73122). Experiments involving the rapid depletion of intracellular Ca2+ stores and Ca2+-free medium demonstrated that the biphasic response of endothelial Ca2+ to serotonin was related to the release of Ca2+ from intracellular stores and to the influx of extracellular Ca2+. We also suggest that serotonin-induced changes in [Ca2+](i) are related to Ca2+ channels sensitive to voltage-operated and inorganic Ca2+ channel blockers. (C) 1999 Elsevier Science B.V. All rights reserved.