Influence of calcium lack and nifedipine on carbachol-, potassium- and quinine-induced contractions of the lizard isolated rectum.

In the lizard isolated rectum, carbachol-, KCl- and quinine-induced contractions were reversibly inhibited by calcium withdrawal. Quinine-induced contractions were more sensitive to calcium lack than were those elicited by carbachol or KCl. Nifedipine inhibited contractile responses induced by all three agonists, but more readily blocked quinine- and carbachol- than KCl-induced contractile responses. It is suggested that extracellular calcium influx stimulated by carbachol, KCl and quinine occurs via different pathways, and that differentiation of calcium channels exists in lizard smooth muscle.