Differences in contractile responses to acetylcholine and serotonin in rat stomach fundus strips

The differences in contractile responses to acetylcholine (ACh) and serotonin (5-HT) were studied in the rat fundus strips. At low temperatures, the contractile response to 5-HT was reduced more noticeably than to ACh. The contraction induced by ACh at 4 degrees C was not inhibited by La3+. Removal of extracellular Ca2+ reduced the response to 5-HT more significantly than that to ACh.. La3+, verapamil and D-600 inhibited the 5-HT response more than the ACh response. In Ca2+-free solution the contractile response to ACh of a fundus strip preloaded with Ca2+ was lar ger than that to 5-HT. These results suggest that the Ca2+ movements induced by ACh and by 5-HT are different, and that the difference in Ca2+ movements may cause the difference in contractile responses to the two agonists at low temperatures.