Figure 2.

Concentration‐dependent increase in I _sc across mucosal–submucosal preparations (1st row) and mucosal preparations (2nd row) from rat distal colon induced by serosal administration of acetylcholine, propionylcholine or butyrylcholine. Because of the desensitization of the I _sc response at higher concentrations, all three choline esters were only administered once to an individual tissue when used in concentrations ≥100 μM, whereas for lower concentrations, they could be administered repeatedly to the same tissue with a washing step between the individual administrations (Methods). The curves show fits to a Hill equation. Hill coefficients were in the range of 0.8–2.2 with the exception of the response to butyrylcholine in the mucosal–submucosal preparation, where the Hill coefficient was 6.6 (for EC₅₀ values, see text). Values are given as increase in I _sc (ΔI _sc) above baseline just prior administration of the respective agonist concentration and are means (symbols) ± SEM (vertical lines). n = 5–8. ACh, acetylcholine; BCh, butyrylcholine; PCh, propionylcholine.