Effect of calcium antagonists on acetylcholine‐induced contractions in longitudinal smooth muscle strips from sheep duodenum

AbstractThe effect of several calcium antagonists on acetylcholine‐induced contractions has been examined in longitudinal smooth muscle strips from sheep duodenum. Contractions induced by 10−5M acetylcholine were inhibited up to 65% in Ca2+‐free solution and were blocked in the absence of extracellular Ca2+plus 1 mM EGTA; 10 mM lanthanum reduced acetylcholine‐induced contractions by 97%: 105mverapamil and W−4mnifedipine reduced contractions by 58 and 42%, respectively, but sodium nitroprusside did not modify these responses: 10−4mtrifluoperazine inhibited acetylcholine‐induced responses by 75%: 10−2mcaffeine produced a contraction; 2 mmprocaine antagonized acetylcholine responses by 85%. We suggest that acetylcholine‐induced contractions were mediated by extracellular Ca2+that enters through a potential‐dependent Ca2+channel by intracellular Ca2+release, probably from sarcoplasmatic reticulum because procaine inhibits the response.