Figure 7. Effect of external pH (pH_o) on background K⁺ current of HAC.

A, currents recorded from a HAC voltage-clamped at a constant holding potential of –110 mV. The cell was initially in 5 mm K⁺, pH_o 7.4, then the solution was switched to 145 mm K⁺ at different pH_o, as indicated. B, ramp I–V relations in 145 mm K⁺, at three different values of pH_o, as indicated (different cell from A). Currents were the average of three consecutive sweeps in each pH_o. Five millimolar TEA was added to all solutions. C, plots of zero-current slope conductance of the (ramp) I–V, in 25 and 145 mm external K⁺, at three values of pH_o. Five millimolar TEA was included in all solutions. The 25 mm K⁺ and 145 mm K⁺ data were from 9 and 19 cells, respectively. Values are means ± SEM. *P < 0.05, compared with pH_o 7.4 (repeated measures ANOVA). D, effect of pH_o on RMP of HAC in 5 and 25 mm external K⁺. Solutions included 5 mm TEA for all recordings of RMP. Data were from 5 cells in 5 mm K⁺ and 9 cells in 25 mm K⁺. For 5 mm K⁺, **P < 0.01 for pH_o 8.5 vs. pH_o 6.0 (repeated measures ANOVA). For 25 mm K⁺, *P < 0.05 and **P < 0.01, compared with pH_o 7.4 (repeated measures ANOVA), respectively.