Prejunctional muscarinic receptors modulating acetylcholine release in rabbit detrusor smooth muscles

We investigated the presence and subtypes of functionally prejunctional receptors in cholinergic nerve endings of rabbit detrusor smooth muscle strips using high-performance liquid chromatography coupled with a microdialysis procedure. The effects of pretreatment with various drugs on acetylcholine (ACh) release and contractile responses induced by electrical field stimulation were evaluated. Although atropine (a muscarinic nonselective antagonist) and 4-DAMP (a muscarinic M3 antagonist) did not influence the ACh release, they markedly reduced the contractile responses. Pirenzepine (M1 antagonist) decreased ACh release and contractile responses. Methoctramine (M2 antagonist) increased the ACh release, but did not influence to the contractile responses. These results suggest that the muscarinic receptors in the rabbit detrusor smooth muscle are heterogeneous, prejunctional facilitatory (M1 receptors), and inhibitory (M2 receptors) for ACh release and postjunctional M3 receptors mediating contractile responses.