Effects of berberine on intracellular free calcium in smooth muscle cells of guinea pig colon

Aim: To investigate the effects and mechanism of berberine (Ber) on the intracellular free calcium concentration ([Ca2+](i)) in the smooth muscle cells of guinea pig colon. Methods: The changes of [Ca2+](i), were assayed by the biwavelength spectrophotometry with Fura 2-AM in the cell suspension of the smooth muscle cells, which were freshly isolated from guinea pig colon. Results: In the resting state, [Ca2+](i) in the HEPES-Ringer solution (CaCl2 1.5 mmol.l(-1)) was (108 +/- 9.4) nmol.l(-1) (n = 7). Ber had no significant effects on the resting [Ca2+](i), but markedly inhibited the increase in [Ca2+](i) induced by 60 mmol.l(-1) KCl in a concentration-dependent manner. The value of IC50 was 34.09 mumol.l(-1). 30 and 100 mumol.l(-1) Ber also inhibited the elevation of [Ca2+](i) evoked by 10 mumol.l(-1) Ach in a dose-dependent fashion in the presence or absence of extracellular Ca2+. In addition, Ber inhibited the elevation of [Ca2+](i) stimulated by cyclopiazonic acid (CPA) in a dose-dependent manner. This effect was more potent in the HEPES-Ringer solution (IC50 = 37.79 mumol.l(-1)) than Ca2+-free medium (IC50 = 49.70 mumol.l(-1)). Conclusions: Ber possessed an inhibitory effect on the influx of extracellular Ca2+ and Ca2+-release from intracellular stores in the smooth muscle cells of colon. That is to say Ber may be a blocker of Ca2+ channels. Copyright (C) 2001 S. Karger AG, Basel.