Figure 9.

Effect of bath acidification with CO₂ on junctional conductance of 32WT and the V181A and E102G mutants. Oocytes were injected with the mRNAs for 32WT, V181A, and E102G and paired homotypically. Both cells were clamped at -30 mV, and junctional conductances were monitored by measuring the current responses in cell 2 to a ±10 mV pulse applied to cell 1 (frequency, 0.5 Hz). After establishing a stable baseline conductance for at least 2 min, the bath was acidified by continuous perfusion with bath solution saturated with CO₂ (arrows). Twelve minutes later, the perfusate was changed to a standard bath solution at pH 7.6 (arrowheads). Junctional conductances were determined at 30 sec intervals and plotted for times beginning 1 min before application of CO₂-saturated solution. As shown, the effects of acidification and realkalinization on the 32WT-induced (a) and V181A-induced (b) junctional conductances were nearly identical, whereas the E102G-induced (c) junctional conductance declines more rapidly and fully; the E102G-induced conductance also shows a longer delay in onset of recovery when CO₂ is removed from the bath. The overshoot seen with realkalinization of the WT and E102G was quite variable; overshoot was not as prominent with the V181A mutant, in which overall protein levels are lower. Overshoot is likely an effect of pH on junctional conductance distinct from any direct effect on channel gating.