RELAXANT EFFECTS OF BRL-38227 AND PINACIDIL ON THE RAT GASTRIC FUNDUS

Concentration-effect curves for BRL 38227 (lemakalim) and pinacidil were obtained in longitudinal muscle strips of the rat gastric fundus contracted by prostaglandin F2-alpha. Both agents induced a concentration-dependent relaxation, with BRL 38227 (EC50 = 3 x 10(-6) M) being more potent than pinacidil (EC50 = 8 x 10(-6) M). Glibenclamide (10(-7), 10(-6) and 10(-5) M) antagonized the relaxant effect of BRL 38227 and pinacidil but neither antagonism was of the simple competitive type. Phentolamine (10(-7), 10(-6) and 10(-5) M) competitively antagonized the effect of pinacidil and non-competitively that of BRL 38227. Glibenclamide had no influence on the relaxant effect induced by vasoactive intestinal polypeptide or by electrical field stimulation in the presence of atropine and guanethidine. The results suggest that glibenclamide-sensitive K+ channels are present in the rat gastric fundus and that they do not mediate the inhibitory response to non-adrenergic, non-cholinergic neurostimulation.