BRADYKININ B2-HYDROXYTRYPTAMINE AND 5-HYDROXYTRYPTAMINE (5-HT2)-RECEPTOR STIMULATED INCREASES IN INTRACELLULAR CALCIUM IN CULTURED GUINEA-PIG AORTIC SMOOTH-MUSCLE CELLS

The effect of 5-hydroxytryptamine (5-HT) and bradykinin on intracellul ar free calcium concentration ([Ca2+]i) has been studied in cultured g uinea-pig aortic smooth muscle cells loaded with the Ca2+-sensitive fl uorescent dye fura-2. Bradykinin and 5-HT elicited rapid increases in [Ca2+]i with log EC50 values of -7.9 +/- 0.05 M (N = 3) and -6.1 +/- 0 .1 M (N = 4), respectively. Both agonists stimulated the release of in tracellular calcium (Ca2+ responses still present in the absence of ex tracellular calcium) and to a lesser extent Ca2+ influx (observed when extracellular calcium was re-applied to cells initially stimulated in nominally Ca2+-free buffer containing 0.1 mM EGTA). The B1-receptor a ntagonist des-Arg9,[Leu8]-bradykinin had no effect on calcium response s elicited 100 nM bradykinin, whereas the B2-receptor antagonist D-Arg [Hyp3,Thi5.8,D-Phe7]-bradykinin (10 muM) inhibited the response to 100 nM bradykinin by 43%. The bradykinin B2-receptor antagonist D-Arg[Hyp 3,Thi5.8,D-Phe7]-bradykinin virtually abolished the response to 10 nM bradykinin (IC50, 4 muM). No increase in [Ca2+]i, was observed with th e B1-receptor agonist des-Arg9-bradykinin (300 nM). The response to 5- HT (100 muM) was abolished by the 5-HT2 receptor antagonist ketanserin (IC50 = 2 +/- 0.4 nM; N = 3). These data suggest that in cultured gui nea-pig aortic smooth muscle cells bradykinin B2- and 5-HT2-receptor a ctivation stimulates the release of Ca2+ from intracellular stores and Ca2+ influx through Ca2+ entry pathways in the plasma membrane.