Key result
Dialysis with 2 mM ATP sustained inwardly rectifying K+ current in bovine retinal pigment epithelial cells, whereas absence of ATP or Mg2+ led to rapid rundown (t1/2 < 2 min).
The sustained activity of inwardly rectifying K+ current in bovine retinal pigment epithelial cells requires intracellular MgATP and likely involves ATP hydrolysis.
ATP dependence of RPE IKir extends channel regulation models; leaves open human disease relevance.
Inwardly rectifying K+ current (IKir) in freshly isolated bovine retinal pigment epithelial (RPE) cells was studied in the whole cell recording configuration of the patch-clamp technique. When cells were dialyzed with pipette solution containing no ATP, IKir ran down completely in <10 min [half time (t1/2) = 1.9 min]. In contrast, dialysis with 2 mM ATP sustained IKir for 10 min or more. Rundown was also prevented with 4 mM GTP or ADP. When 0.5 mM ATP was used, IKir ran down by approximately 71%. Mg2+ was a critical cofactor because rundown occurred when the pipette solution contained 4 mM ATP but no Mg2+ (t1/2 = 1.8 min). IKir also ran down when the pipette solution contained 4 mM Mg2+ + 4 mM 5'-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. We conclude that the sustained activity of IKir in bovine RPE requires intracellular MgATP and that the underlying mechanism may involve ATP hydrolysis.
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Hughes et al. (1998) studied this question. Intracellular ATP/MgATP dialysis vs. No ATP, no Mg2+, or nonhydrolyzable ATP analogs was evaluated on Inwardly rectifying K+ current (IKir) rundown. Dialysis with 2 mM ATP sustained inwardly rectifying K+ current in bovine retinal pigment epithelial cells, whereas absence of ATP or Mg2+ led to rapid rundown (t1/2 < 2 min).
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