Table 2.

Inhibition of EFS-induced and acetylcholine-induced cholinergic contractions of guinea-pig trachealis

Compound	IC50 (μm)	Kb (μm)
FM2-10	1.6 ± 0.1	15.8 ± 10
FM1-43	0.4 ± 0.1	0.33 ± 0.15
Atropine	0.0006 ± 0.0003	0.0017 ± 0.0009
Pirenzepine	1.6 ± 0.6	0.13 ± 0.02
Methoctramine	12.9 ± 4.6	>3 μm
4-DAMP	0.0021 ± 0.0002	0.00077 ± 0.00009

Data represent the means ±s.e.m. of n = 3–4 experiments. The IC₅₀ is defined as the concentration of antagonist that inhibits the maximum EFS-evoked contractions by 50%. The K_b is the concentration of antagonist producing a 2-fold leftward shift in the acetylcholine concentration–response curve. The absolute potency and rank order of potency for the reference compounds is comparable to that reported previously in studies of muscarinic receptor agonist-induced contractions of guinea-pig trachealis (Eglen et al. 1999).