VY sequence in TM1 is not sufficient to abolish fast desensitization. The effect of mutations in TM1 of the γ2L subunit on desensitization and deactivation kinetics was determined. The YF pair was mutated, singly and together, in the γ2L subunit to the corresponding VY residues of the δ subunit, and expressed with α1 and β3 subunits. The middle column illustrates representative currents. Bar graphs are as in Figure 2. The rate and relative contribution of fast desensitization was not altered by any of the mutations compared to wild-type γ2L subunit-containing receptors. However, the weighted deactivation was significantly accelerated by both the single mutations and the double mutation in TM1. Theasterisk indicates significant difference from both αβδ (p < 0.05) and αβγ (p < 0.01) receptors. Horizontal calibration: 400 msec; vertical calibration: 180 pA for γ2L_(YΔV), 53 pA for γ2L_(FΔY), and 72 pA for γ2L_(YFΔVY).