Abstract: | Inwardlyrectifying K+ current(IKir) infreshly isolated bovine retinal pigment epithelial (RPE) cells wasstudied in the whole cell recording configuration of the patch-clamptechnique. When cells were dialyzed with pipette solution containing noATP, IKir randown completely in <10 min half time(t1/2) = 1.9 min]. In contrast, dialysis with 2 mM ATP sustainedIKir for 10 min or more. Rundown was also prevented with 4 mM GTP or ADP. When 0.5 mMATP was used,IKir ran down by~71%. Mg2+ was a criticalcofactor because rundown occurred when the pipette solution contained 4 mM ATP but no Mg2+(t1/2 = 1.8 min).IKir also randown when the pipette solution contained 4 mMMg2+ + 4 mM5'-adenylylimidodiphosphate(t1/2 = 2.7 min)or 4 mM adenosine 5'-O-(3-thiotriphosphate)(t1/2 = 1.9 min),nonhydrolyzable and poorly hydrolyzable ATP analogs, respectively. Weconclude that the sustained activity ofIKirin bovine RPE requires intracellular MgATP and that the underlyingmechanism may involve ATP hydrolysis. |