The homologous mutation in the a-subunit (aL263S) also
increased the sensitivity to GABA, although to a lesser extent
than bL259S with an EC50 ¼ 0.2470.03 mM for aL263S as
compared to 0.07870.005 mM for bL259S (Chang & Weiss,
1999). The position of a1L263Sb2g in terms of L is indicated
by the rightmost vertical line in the inset of Figure 2a. In this
case, we would predict that DZP, in contrast to bL259S where
the sensitivity was maximally shifted, could further increase
the sensitivity to GABA. In fact, we observed an increase in
GABA-mediated sensitivity for aL263S (EC50 ¼ 0.147
0.02 mM) and this increase in sensitivity was approximately
twofold as was the DZP-mediated shift for the wild-type
receptor (compare Figures 1b and 2b and see Table 1).