Acetylcholine receptor inactivation in torpedo californica electroplax membrane vesicles. Detection of two processes in the millisecond and second time regions

Summary The rates of inactivations of the acetylcholine receptor-controlled ion flux were measured with membrane vesicles prepared from the electric organ of Torpedo californica . A flow quench technique with a time resolution of 2 msec was used. The vesicles were preincubated with carbamylcholine for various periods of time and then the rate of 86 Rb + influx was measured. The influx rate decreased progressively with the length of preincubation time. This decrease (inactivation) in influx rate occurred in two different time zones. A fast inactivation process with a half-time of ∼300 msec resulted in at least a 60-fold decrease of ion flux rate. The remaining ion flux activity decreased to an undetectable level in a slow inactivation process with a half-time of 6–7 seconds. Previously, only one inactivation process has been observed by ion flux measurements with receptor-rich vesicles from Electrophorus electricus or Torpedo species.