The action of the ionophores, X-537A and A-23187, on smooth muscle

The cation ionophore X 537A in the concentration range of 10^-6 to 3 x 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 x 10^-5M. 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.