Andrographis paniculata (Nees) selectively blocks voltage-operated calcium channels in rat vas deferens

The possible blockade of voltage-operated calcium channels (VOCs) by Andrographis paniculata dried extract in vas deferens smooth muscle was investigated in rats. The tissues were incubated in Ca 2+-free Kreb’s solution and stimulated with KCl (40 mM) to produce depolarisation of the membrane. The isometric contractile response to cumulative concentrations of CaCl 2 was effectively blockaded by 0.2 and 0.4 mg/ml A. paniculata. In other experiments, the maximum contractile response induced by norepinephrine was not antagonised by 0.2, 0.4 or 0.8 mg/ml A. paniculata. The possible blockade of Ca 2+ entry by A. paniculata was evaluated with 45Ca 2+ uptake in vas deferens treated with reserpine (5 and 2.5 mg/kg) 48 and 24 h before the experiments. Epididymal segments were incubated with Ca 2+-free Kreb’s solution with KCl, 25 and 50 mM. The influx was completely blockaded with 0.4 mg/ml A. paniculata. These results suggest that A. paniculata selectively blockades VOCs, hence inhibiting the 45Ca 2+ influx.