The action of the ionophore ionomycin in guinea-pig intestinal smooth muscle

Abstract

The ionophore ionomycin produced concentration-dependent (5 × 10−9 to 5 × 10−6 M) contractions in guinea-pig ileal longitudinal smooth muscle. Responses were dependent on extracellular Ca2+, consistent with the known role of this Ca2+ source in supporting excitation–contraction coupling to a variety of stimulants in this tissue. Responses were insensitive to atropine (10−6 M) but were dependent upon extracellular Na+ and were completely blocked by low concentrations of the Ca2+-channel antagonists nicardipine. YC-93 (5 × 10−7 M), and D-600 (5 × 10−6 M). The behaviour of ionomycin is very similar to that shown by A 23187 in this tissue. Ionomycin, like A 23187, can apparently activate D-600 sensitive Ca2+ channels in the guinea-pig intestinal smooth muscle rather than simply translocating Ca2+EXT.