Figure 4.

ATP fails to activate RKR/AAA‑expressing hIK1 channels. (A) Following patch excision into 10 mM free Ca²⁺ plus 1 mM ATP, RKR/AAA‑expressing channels exhibit a rapid decrease in current, so‑called “rundown.” Subsequent addition of DCEBIO (10 mM) increases current which is reversed upon -washout. (B) Following patch excision into 10 mM free Ca²⁺, in the absence of ATP, wild‑type hIK1 channels exhibit a slow rundown. Removal of Ca²⁺ from the bath results in an immediate inhibition of channel activity, which is restored upon re-addition of Ca²⁺. The subsequent addition of ATP (1 mM) results in a large increase in channel activity, which is completely inhibited by returning to zero Ca²⁺. (C) Excising RKR/AAA‑expressing channels into 10 mM free Ca²⁺, in the absence of ATP, results in a rapid rundown of channel activity. Addition of ATP (1 mM) does not increase channel activity, although the subsequent addition of DCEBIO (10 mM) results in a large increase in channel activity, which is reversed following washout of DCEBIO.