Figure 3.
Single-channel activity induced by PB. (A) Single-channel activity from two (left and right) rapidly perfused outside-out membrane patches from cells expressing α1β2γ2S GABARs. (Top) Liquid junction potential response (see Materials and methods) representing the time course of PB pulses (upward deflection, 300 msec) indicated concentrations (μM) that were delivered every 15 s. 500-μM patch contains two active channels, whereas the 3,000-μM patch contains three active channels. (Middle) Four stacked representative single-channel records triggered by PB application. Downward current deflections mark openings of single α1β2γ2S GABARs, with primary unitary current marked by dashed lines. The primary conductance of 27 pS was calculated using primary unitary current and an Ohmic relationship (chloride reversal potential = 0 mV; holding potential = −70 mV). (Bottom) Ensemble current average (irregular line) and solid line marks baseline. The vertical scale bars reflect single-channel amplitudes. (B, top) Selected periods of records from A to illustrate the difference in apparent open times under the indicated conditions. (Bottom, left) Open-time histograms from patches of A at the indicated concentrations. Solid line marks fitted monoexponential functions with the indicated time constants. Higher PB concentration reduces open time by approximately twofold, consistent with previous results and consistent with a blocking process acting on a single open state. (Right) Grouped data for time constants of open-time histograms for the indicated conditions (n = 3–4 patches). The asterisk indicates the difference with other groups (P < 0.05; unpaired t test; see Results).