Serotonin-stimulated increase in cytosolic Ca(2+) in cultured rat heart endothelial cells

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