Doğan, N.Çiçek, E.Cenik, A. G.Sıngırık, E.Kılıç, M.Özcan, A. S.2020-03-262020-03-261991Doğan, N., Çiçek, E., Cenik, A. G., Kılıç, M., Özcan, A. S., (1991). 5-Hydroxytryptamine-Induced Contraction of Human Isolated Umbilical Artery and Its Dependence on Cellular and Extracellular Ca++. Archives Internationales De Pharmacodynamie Et De Therapie, 312, 79-85.0003-9780https://hdl.handle.net/20.500.12395/16105The contribution of intra- and extracellular Ca++ during KCl- and 5-hydroxytryptamine-induced contractions was investigated in human isolated umbilical arteries obtained from cords of normal full-term deliveries. In normal solution, nifedipine caused dose-dependent relaxations of the arteries contracted by high K+ (80 mM) and 5-hydroxytryptamine. The IC50 value of nifedipine on KCl-induced contractions was about 9 times lower than that on 5-hydroxytryptamine-induced contractions. In Ca++-free medium, KCl failed to induce contractions of the artery. However, 5-hydroxytryptamine caused contractions amounting to 52 % of the maximum response obtained by re-addition of Ca++, and this response was abolished by 10(-6) M of nifedipine. In the presence of either KCl or 5-hydroxytryptamine, subsequent addition of Ca++ caused reproducible contractions which were also inhibited by nifedipine. These results indicate that the KCl-induced contraction of human isolated umbilical artery is mainly dependent on extracellular Ca++, whereas that induced by 5-hydroxytryptamine involves both intra- and extracellular Ca++. It is also suggested that nifedipine does not only inhibit the influx of extracellular Ca++ during the contraction by 5-hydroxytryptamine but that it may also have intracellular effects.eninfo:eu-repo/semantics/closedAccessArticle31279851772342N/AWOS:A1991GT04900006N/A