Comparison of nAChR inhibition by the open channel blocker QX-222 (100
μM, A and B) and by azietomidate (10 μM, C and D). T.
californica nAChRs were exposed simultaneously to 300 μM ACh and
inhibitor according to four different protocols that are numbered on the
traces: 1) 800 ms of ACh, before return to buffer; 2) 800 ms of ACh +
inhibitor, before return to buffer; 3) 30 ms of ACh + QX-222 (A) or 100 ms of
ACh + azietomidate (C), before return to buffer; or 4) 30 ms of ACh + QX-222
(B) or ACh + azietomidate (D), before return to ACh alone for 170 ms. In each
panel, the bar above the current traces indicates the duration of exposure to
ACh and QX-222 or azietomidate before switching the patch to a stream of
buffer (A and C) or ACh (B and D). A and B are all from a single patch, as are
those from C and D. Each trace is an average of four sweeps, with a 20- to
120-s buffer wash between each trial.