AIM In order to understand the 5 HT induced Ca 2+ influx characterization and the relationship between chloride channels and the Ca 2+ influx, we studied the effects of Ca 2+ blockers(nimodipine and SK&F96365) and Cl -channel blockers(DIDS and NPPB) on 5 HT and cyclopiazonic acid(CPA) induced Ca 2+ influx in cultured rabbit basilar artery smooth muscle cells. METHODS We measured i of cultured rabbit basilar artery smooth muscle cells growing on glass coverslips using ratiometric video fluorescence microscopy and the Ca 2+ sensitive dye, fura 2. RESULTS ①It was found that application of 5 HT and CPA gave rise to biphasic i elevation.5 HT only triggered a fraction of CPA sensitive Ca 2+ store, which was enough to activate Ca 2+ entry; ②Nimodipine had no effect on both 5 HT and CPA induced Ca 2+ entry, while SK&F96365 inhibited them; ③DIDS and NPPB inhibited 5 HT and CPA induced Ca 2+ influx in a concentration dependent manner. Ca 2+ influx was further inhibited by DIDS or NPPB after the maximal inhibition by SK&F96365. SK&F96365 also further inhibited the Ca 2+ influx which had been inhibited by DIDS or NPPB. CONCLUSION These data suggest that 5 HT induced Ca 2+ influx in cultured rabbit basilar artery smooth muscle cells is related to non VDC, which includes CRAC and non CRAC parts, and DIDS or NPPB sensitive Cl -channel is related to this Ca 2+ influx.