Characterization of muscarinic receptors in rat bronchial smooth muscle invitro

This study was undertaken to assess the important muscarinic receptor subty pe in acetylchohne (ACh)-induced rat bronchial smooth muscle contraction. R ing smooth muscle strips of the left main bronchus were used. Isometrical c ontraction was measured in response to ACh in cumulative concentrations (10 (-7)-10(-3) M) with and without preincubations with the muscarinic receptor antagonists, pirenzepine tan M, antagonist), methoctramine tan M-2 antagon ist), and 4-diphenylacetoxy N-methylpiperidine (4-DAMP; an M-1/M-3 antagoni st). Preincubation with these antagonists resulted in concentration-depende nt rightward shifts of the concentration-response curves to ACh. pA(2) valu es (means +/- sem) were 8.80+/-0.10 for 4-DAMP, 7.03 +/- 0.06 for pirenzepi ne and 5.91+/-0.36 for methoctramine, indicating that the most important mu scarinic receptor mediating ACh-induced contraction of rat bronchial smooth muscle is of the M-3 type.