The long-lasting contraction induced by transmural stimulation in the longitudinal muscle of the guinea-pig gastric corpus.

The mechanisms involved in the long-lasting contraction induced by transmural stimulation were investigated in the isolated longitudinal muscle of the guinea-pig gastric corpus. Transmural stimulation induced an initial rapid contraction, a subsequent relaxation and a long-lasting contraction which was mimicked closely by the responses to noradrenaline and ATP. The rapid contraction was blocked by tetrodotoxin or by atropine, and the subsequent relaxation was also blocked by tetrodotoxin, but not by atropine. The long-lasting contractions were not inhibited by atropine, phentolamine, and propranolol. However, some of those were partially inhibited by tetrodotoxin and guanethidine, and others were enhanced by tetrodotoxin. The noradrenaline- but not ATP-induced long-lasting contraction was blocked by phentolamine. Furthermore, indomethacin completely abolished the long-lasting contractions induced by transmural stimulation, noradrenaline, and ATP, but did not significantly affect the response to prostaglandin E2. The results indicate that the long-lasting contraction induced by transmural stimulation is mediated through prostaglandins release which may be triggered by neuro-transmitters or by endogenous substances.