Characterisation of the effects of acetylcholine (ACh; 10-5 M) in isolated pulmonary bronchi pre-constricted with U46619 (U4; 10-7 M). Panel A shows an original recording from a typical experiment. After equilibration, bronchi were contracted with U46619 (10-7 M), at plateau ACh was added and further contraction was observed. At plateau either L-NG-nitro-L-arginine methyl ester (L-NAME; 10-3 M) or apamin (5 × 10-7 M) plus charybdotoxin (10-7 M) was added, once a further plateau was achieved apamin plus charybdotoxin or L-NAME were added respectively. Panels B and C show pooled data from several experiments where L-NAME or apamin plus charybdotoxin were added individually. The data is expresses as the mean percentage of U46619-induced tone +/- the S.E.M and comprised of n = 4–5 experiments. A p-value of < 0.05 was taken as statistically significant, calculated by t-test and denoted by *.