6533b829fe1ef96bd128ab5a

RESEARCH PRODUCT

Pre- and Postjunctional Muscarinic Receptors in the Guinea-pig Trachea

subject

description

ABSTRACT The effects of M2- and Me-selective muscarinic antagonists on electrically evoked [3H]acetylcholine release and muscle contraction were compared in the isolated guinea-pig trachea. The M2-selective antagonists methoctramine and AF-DX 116 were more potent in enhancing the evoked release than in inhibiting the contractile response. As a consequence of the selective blockade of the inhibitory autoreceptors the evoked muscle contractions were enhanced by low concentrations (0.1 μmol/l) of the M2-selective antagonists. The Me-selective antagonists 4-DAMP, UH-AH 37 and pFHHSiD were more potent in reducing the contraction than in facilitating the evoked release. Surprisingly, HHSiD did not discriminate between pre- and postjunctional receptors. It is concluded that autoinhibition of acetylcholine release is mediated via an “M2-like” receptor whereas muscle contraction is due to stimulation of an M3-receptor.