Contractile effects caused by thaliporphine in the guinea-pig ileum

The intestinal effects of thaliporphine, a potent vasoconstrictor, were studied using the isolated guinea-pig ileum. Thaliporphine (0.1-100 microM) caused contraction in a concentration-dependent manner. The contraction was not affected by pretreatment of the ileum with tetrodotoxin, phentolamine, prazosin, propranolol, naloxone, atropine, diphenhydramine, methysergide, indomethacin or staurosporine. However, the contraction was inhibited markedly by nifedipine and verapamil. These results suggest that thaliporphine causes contraction of intestinal smooth muscle by a direct effect on muscle mediated by an increased Ca2+ influx through voltage-dependent Ca2+ channels.