STEREOSELECTIVITY OF BUTYLIDENEPHTHALIDE ON VOLTAGE-DEPENDENT CALCIUMCHANNELS IN GUINEA-PIG ISOLATED ILEUM

Two geometric isomers, the Z- and the E-forms, can be separated from s ynthetic mixtures of butylidenephthalide (Bdph). Z-Bdph (50-100 mu M) non-competitively inhibited Ca2+-induced contractions in depolarized ( K+, 60 mM) guinea-pig ileum longitudinal smooth muscle, with a pD(2)' value of 3.88 +/- 0.20 (n = 5). However, E-Bdph (20-100 mu M) competit ively inhibited these contractions with a pA(2) value of 4.56 +/- 0.18 (n = 5) which was significantly (P < 0.05) greater than the pD(2)' va lue of Z-Bdph. In contrast, the two isomers had no stereoselective inh ibitory action on Ca2+ influx through pre-or past-junctional membranes of cholinergic nerve endings from which the transmitter acetylcholine is released or on Ca2+ release from intracellular stores. Therefore, the trans-Z and cis-E forms of Bdph might have geometric stereoselecti vity for voltage-dependent calcium channels (VDC) in guinea-pig longit udinal smooth muscle. Both isomers might inhibit more selectively the contractile twitch responses evoked by electrical stimulation than by cumulative acetylcholine- or carbachol-induced transient contractions in guinea-pig ileum longitudinal smooth muscle.