Abstract: AIM To observe the effect of different concentrations of IL-1β on the membrane potential of vascular smooth muscle cells and to investigate the mechanism of IL-1β in regulating large conductance Ca2+-activated K+ channel (BKca) activity in vascular smooth muscle cells by H2O2. METHODS Rat aortic smooth muscle cells (ASMC) were grouped by time and IL-1β concentration. The membrane potential of ASMC labeled with membrane potential probe DIBAC4 (3) was detected by confocal laser scanning microscopy and the effect of IL-1β on ASMC membrane potential was observed when catalase (hydrogen peroxide scavenger), IBTX (BKca channel opener), NS1619 (BKca channel blocker) and 4-AP (Kv channel blocker) were used. RESULTS IL-1β had a bidirectional regulation effect with concentration dependent characteristics on ASMCs membrane potential: short time treatment resulted in membrane potential hyperpolarization and long time treatment resulted in membrane potential depolarization. IL-1β regulated BKca channels via H2O2, thereby affecting membrane potential. ASMCs-treated IL-1β for short time regulated membrane potential by H2O2 and for prolonged time modulated membrane potential, in part, through H2O2. CONCLUSIONThe role of IL-1β in biphasic regulation of membrane potential in vascular smooth muscle cells may be achieved by H2O2 up-regulation of BKca channel activity (short time) or down-regulation of BKca channel activity (for a long time).