The Action of the Ionophores, X-537A and A-23187, on Smooth Muscle

Abstract

The cation ionophore X-537A in the concentration range of 10−6 to 3 × 10−5 M produced contractions in the rat and guinea-pig vas deferens. No contractile effect was produced in either of the vasa deferentia preparations by the ionophore A-23187 in the concentration range of 10−7 to 5 × 10−5 M. In contrast, X-537A had no contractile effect on the guinea-pig ileal longitudinal smooth muscle while A-23187 produced a dose and [Ca2+] dependent contraction.The contractile effect of X-537A in the vasa deferentia preparations is abolished by phenoxybenzamine or prior reserpine treatment and is therefore attributed to the release of norepinephrine. The effect of A-23187 in the intestinal smooth muscle is attributed to a direct Ca2+ transporting action since its contractile effect is unaffected by histamine, acetylcholine, or 5-hydroxytryptamine antagonists.