We have examined the effects of high concentrations of cholinergic
agonists on currents through single acetylcholine receptor (AChR)
channels on clonal BC3H1 cells. We find that raised concentrations of
acetylcholine (ACh; above 300 microM) or carbamylcholine (Carb; above
1,000 microM) produce a voltage- and concentration-dependent reduction
in the mean single-channel current. Raised concentrations of
suberyldicholine (Sub; above 3 microM) produce a voltage- and
concentration-dependent increase in the number of brief duration
low-conductance interruptions of open-channel currents. These
observations can be quantitatively described by a model in which agonist
molecules enter and transiently occlude the ion-channel of the AChR.
