MUSCARINIC RECEPTOR SUBTYPES IN SMOOTH MUSCLE FROM THE BODY OF HUMAN STOMACH

Up to date, there are four pharmacologically characterized subtypes of muscarinic receptors (M1, M2, M3 and M4). In our study we have investigated muscarinic receptor subtypes in smooth muscle layers of human stomach. Isolated preparations of longitudinal and circular muscle layers from human stomach were used. Acetylcholine, bethanechol, carbachol, pilocarpine and AHR -602 produced concentration-dependent tonic contractions of isolated preparations of both longitudinal and circular muscle layers. Only pilocarpine increased the amplitude of spontaneous contractions of circular muscle preparations. Atropine, trihexyphenidyl, pirenzepine, telenzepine, hexocyclium, gallamine and scopolamine butylbromide concentration-dependently blocked tonic contractions of isolated preparations of both circular and longitudinal muscle layers caused by acetylcholine. Pancuronium did not block tonic contractions caused by acetylcholine, while para-fluoro-hexahydro-sila-difenidol (pFHHSiD) produced weak concentration-dependent blockade of tonic contractions caused by acetylcholine in circular muscle preparations only. The most potent antagonists were M1 selective antagonists: trihexyphenidyl, telenzepine and hexocyclium. These results suggested a predominance of the M1 muscarinic receptor subtype in smooth muscle of the human stomach.