Figure 12.

Effect of external Ca on pH titration of Kir1.1b. Solid lines depict the K dependence of pKa in 5 mM external Ca (1 mM Mg) at an external K of 1 mM (red), 10 mM (green), and 100 mM (blue). Removal of external divalents eliminated the K dependence of the Kir1.1-pKa (dashed lines). Inset shows the apparent pKa as a function of external [K] at four different external Ca concentrations. All data were obtained by progressive internal acidification of the oocytes and were normalized to the value at the highest pH tested (n = 4 oocytes at each K).