Nantenine blocks muscle contraction and Ca2+ transient induced by noradrenaline and K+ in rat vas deferens

Abstract

The effect of nantenine, an aporphine alkaloid isolated from Ocotea macrophylla H.B.K., was studied on contractions and Ca2+ translocation induced by noradrenaline, Ca2+, or K+ in the isolated rat vas deferens from reserpinized animals. Concentration-response curves of calcium chloride (CaCl2) were performed in the vas deferens, in a Ca2+-free nutrient solution, using potassium chloride (KCl, 80 mM) as a depolarizing agent. in these conditions, nantenine (2.35 X 10(-4) and 4.7 x 10(-4) M) significantly reduced the maximum contractions (E-max) of Ca2+ (IC50 = 2.6 x 10(-4) M) and noradrenaline (IC50 = 2.9 x 10(-4) M). the contractile responses were totally recovered after the withdrawal of nantenine. in addition, experiments performed to measure simultaneously the contraction and the increase of intracellular Ca2+ induced by noradrenaline (10(-5) M) or KCl (80 mM) showed that nantenine (2.35 x 10(-4) and 4.7 x 10(-4) M) significantly decreased both effects. the results suggest that a reversible block of Ca2+ entry could be involved on the non-competitive-like antagonism of nantenine in rat vas deferens. (C) 2003 Elsevier Science B.V. All rights reserved.