BK and IK are present in the apical PM. Experiments were performed using the techniques described in Fig. 3 to analyze the contribution of IK and BK to the currents evoked by apical photolysis. (A) K⁺ currents could be evoked in the presence of either TRAM-34 (left) or paxilline (middle) but were essentially abolished when cells were incubated with both agents. (B) Similar experiments were performed in BK-null animals (Slo^−/−). The baseline current was reduced, but apical photolysis resulted in an increase in the remaining IK current, which was markedly reduced in the presence of TRAM-34. However, Cl⁻ currents could be evoked by apical photolysis in the same cells (right).