Figure 3. Effects of pH_i on macroscopic Kir4.1 currents.

A, Kir4.1 currents were recorded from a giant patch with equal concentrations of K⁺ (150 mM) on each side of the membrane. Inward rectifying currents were seen at pH 7.4 using a slope command potential from +100 mV to −100 mV. When the pH in the internal solution was reduced to 6.6, the amplitude of these currents increased by 16 %. Further decreases in pH_i caused strong inhibitions of these currents. Inward rectifying currents were totally suppressed at pH 5.4. Washout led to a recovery of these currents to the baseline level. Note that 4 superimposed traces are shown in each panel. B, the relationship of Kir4.1 currents with pH_i. Kir4.1 currents increase with a modest intracellular acidification (pH 6.6, 7.0), and are strongly inhibited by further acidification. At pH 5.4–6.6, the relationship of Kir4.1 currents (I) to pH_i can be expressed with the Hill equation (continuous line): I = 1/{1 + (pK/pH_i)^n_H}, where pK is the midpoint pH value for channel inhibition, and n_H the Hill coefficient. The pK and n_H here are pH 5.95 and 2.7, respectively.