Acetylcholine-induced receptor-controlled ion flux investigated by flow quench techniques

Using a quench flow technique with membrane vesicles, the acetylcholine receptor-controlled transmembrane ion flux and the inactivation of the receptor with acetylcholine were measured in the msec time region. The ion flux was followed by influx of radioactive tracer ion and the inactivation was followed by an ion flux assay of receptor pre-incubated with ligand. The measurements covered a concentration range to complete saturation of the $\text{active}$ state of the receptor with ligand, and were consistent with a minimal model previously proposed on the basis of experiments with carbamylcholine. The ion translocation rate at saturation with acetylcholine is about twice that at saturation with carbamylcholine and this reflects a more favored channel opening equilibrium for acetylcholine.