Figure 3.

Starting pH_i, reference pH_i, and representative pH_i tracings from pNBC1-transfected and untransfected HEK293 cells. A, B: Box and whisker diagram of the starting- and reference pH_i values from pNBC1-transfected and untransfected cells. Steady-state pH_i was significantly higher in transfected cells, pointing to increased baseline Na⁺/HCO₃^- cotransport activity (*: p < 0.001, Student's t-test for paired samples, n = 7). The reference pH_i after acidification was, however, not different between the two. C: After imposing an acid load using the "NH₄-prepulse" method, cells acidified to a similar extent. Upon Na⁺ readdition, most untransfected cells showed no significant recovery, while pH_i increased rapidly in transfected cells (representative tracings). It should be noted that our 2-point calibration approach is optimized for the low pH_i values at which transporter activity is measured, and that the higher pH_i values are therefore overestimated.