EPHEDRINE BLOCKS WILD-TYPE AND LONG-LIVED MUTANT ACETYLCHOLINE-RECEPTOR CHANNELS

A combination of transient expression of wild-type and a mutant muscle nicotinic receptor (AChR) found in a patient suffering from a congeni tal myasthenic syndrome and single-channel recordings was used to char acterize the action of ephedrine on the AChR. In the presence of ephed rine, both types of AChR channel showed a flickering behaviour and a d ose-dependent reduction in the mean open time. The duration of the blo cking events was dependent on the membrane potential. The forward rate constant for the blocking process was of the order of 10(7) M-1 s(-1) in both types of AChR. The results are consistent with ephedrine acti ng as a channel blocker in wild-type AChR as well as in long-lived ACh R channels present in patients with the slow-channel syndrome.