Two desensitization processes of GABA receptor from rat brain. Rapid measurements of chloride ion flux using...

Two rapid phases of GABA receptor desensitization, which proceeded with a 10-fold difference in rates, were detected in two types of experiment with membrane vesicle preparations from rat cerebral cortex. The time course of GABA-mediated 36Cl- influx progressed in two phases. The 36Cl- influx was decreased, by preincubation with GABA, in two phases. Measurements were made in the time range 10-1000 ms. The major loss of channel opening activity occurred in the faster phase, which was complete in 100 ms with saturating GABA concentrations. The remaining activity decreased in a slower phase in a few seconds with a 10-fold slower rate. The faster phase of desensitization was more than 10-fold faster than previously observed and the slower phase was slightly faster than previously reported measurements with GABA receptor. Both desensitization processes had a similar dependence on GABA concentration with a half response at approximately 100 microM GABA.