Involvement of the muscarinic receptors in the postsynaptic potentiation of neurogenic twitch contraction in the mouse vas deferens.

Muscarinic agonists and three selective antagonists were used in an attempt to characterize the muscarinic receptor subtypes which regulate the electrically evoked, neurogenic twitch contraction of the mouse vas deferens. The neurogenic contraction was concentration-dependently potentiated by both carbachol and oxotremorine, but not McN-A-343. These agonists also potentiated the contraction of unstimulated preparations elicited by exogenous ATP. However, potentiation of the neurogenic twitch contraction was strongly antagonized by pretreatment with 4-DAMP (IC50 = 1.38 nM for carbachol, and 4.79 nM for oxotremorine). The inhibitory effects of methoctramine and pirenzepine (PRZ) were about 100 times lower than those of 4-DAMP; the descending order of antagonistic potencies was: 4-DAMP much greater than methoctramine approximately equal to PRZ. These results suggest that muscarinic receptors are involved in the postsynaptic potentiation of the neurogenic twitch contraction in the mouse vas deferens. Classifications for the muscarinic receptor subtypes were discussed.