Disruption of CD-I salt bridges reduces Kir2.1 channel activity. (A) Current response to a 1-s voltage ramp from −100 to 100 mV. Currents were recorded in the cell-attached configuration (black), after patch excision (red), and after application of PIP₂ (5 µg/ml; blue). (B) PIP₂ potentiation of Kir2.1 channel excised currents; means ± SEM; *, P < 0.05 relative to WT means; †, P < 0.05 relative to R204A means (Student’s t test).