Effect of 5-hydroxytryptamine on intracellular calcium dynamics in cultured rat vascular smooth muscle cells

The present study elucidated the precise mechanism of 5-hydroxytryptamine (5-HT)-induced increase of intracellular Ca2+ concentration (Ca2+]i) in cultured vascular smooth muscle cells isolated from rat aortic media. Ca2+]i was measured using fluorescent Ca2+ indicator, fura-2. 5-HT caused a dose-dependent increase in Ca2+]i, which was completely inhibited by ketanserin. alpha-Methyl-5-HT had an equipotent effect to 5-HT. Diltiazem at 10 microM partially suppressed the 5-HT-induced increase in Ca2+]i. 5-HT also augmented Mn2+ influx, when monitored by Mn2+ quenching of fura-2 fluorescence. When extracellular Ca2+ (1.3 mM) was removed, a decrease in resting level and a small, transient increase in Ca2+]i were observed. 5-HT stimulation also induced an increase in the production of inositol triphosphate. 5-HT-induced increase in Ca2+]i was significantly, but partially inhibited by staurosporin and H-7. Phorbol 12-myristate 13-acetate induced an increase in Ca2+]i, which was abolished by removal of extracellular Ca2+. 5-HT-induced increase in Ca2+]i was not affected by the pretreatment with pertussis toxin (PTX), and was not accompanied by a change in cyclic AMP content. These results suggest that, in cultured rat aortic smooth muscle cells, 5-HT increases Ca2+]i via 5-HT2 receptor subtype by inducing influx of extracellular Ca2+ partially through L-type voltage-dependent Ca2+ channel, as well as by mobilizing Ca2+ from its intracellular stores. Activation of protein kinase C may be positively involved in the regulatory mechanism of Ca2+ influx, but PTX-sensitive G protein and cyclic AMP seem to be not involved.