ATP-DEPENDENT REGULATION OF INWARDLY RECTIFYING K-PIGMENT EPITHELIAL-CELLS( CURRENT IN BOVINE RETINAL)

Inwardly rectifying K+ current ( I-Kir) in freshly isolated bovine ret inal pigment epithelial (RPE) cells was studied in the whole cell reco rding configuration of the patch-clamp technique. When cells were dial yzed with pipette solution containing no ATP, I-Kir ran down completel y in <10 min [half time (t(1/2)) = 1.9 min]. In contrast, dialysis wit h 2 mM ATP sustained I-Kir for 10 min or more. Rundown was also preven ted with 4 mM GTP or ADP. When 0.5 mM ATP was used, I-Kir, ran down by similar to 71%. Mg2+ was a critical cofactor because rundown occurred when the pipette solution contained 4 mM ATP but no Mg2+ (t(1/2) = 1. 8 min). I-Kir,, also ran down when the pipette solution contained 4 mM Mg2+ + 4 mM 5'-adenylylimidodiphosphate (t(1/2) = 2.7 min) or 4 mM ad enosine 5'-O-(3-thiotriphosphate) (t(1/2) = 1.9 min), nonhydrolyzable and poorly hydrolyzable ATP analogs, respectively. We conclude that th e sustained activity of I-Kir in bovine RPE requires intracellular MgA TP and that the underlying mechanism may involve ATP hydrolysis.