GABA concentration–response relationship and paired pulse analysis for αβγ and αβγ_(YFΔVY) isoforms. A, Whole-cell concentration–response curves were generated for αβγ and αβγ_(YFΔVY) isoforms using rapid perfusion. Currents were normalized to the maximal peak current for each cell. The relation was fit with a sigmoidal curve (see Materials and Methods). Each curve was obtained from the mean responses of seven cells. B, Brief (5–10 msec) pulses of 1 mmGABA were applied to excised outside-out patches at various intervals to investigate paired pulse depression of αβγ GABARs. Note the different horizontal time scales in B andC. Intervals in B were 100, 200, 400, and 800 msec. Similar results were obtained in three other patches. C, Same paradigm as in B, except shorter interpulse intervals were used to emphasize the decrease in paired pulse depression observed for αβγ_(YFΔVY) GABARs. Intervals inC were 10, 25, 50, 100, and 200 msec. Similar results were obtained in three other patches.