Effects of Berberine on Intracellular Free Calcium in Smooth Muscle Cells of Guinea Pig Colon

Abstract

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⁺]_iinduced by 60 mmol·l^–1 KCl in a concentration-dependent manner. The value of IC₅₀was 34.09 µmol·l^–1. 30 and 100 µmol·l^–1 Ber also inhibited the elevation of [Ca²⁺]_i evoked by 10 µmol·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 µmol·l^–1) than Ca²⁺-free medium (IC₅₀ = 49.70 µmol·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.