Kir2.2 inward rectifier potassium channels are inhibited by an endogenous factor in Xenopus oocytes independently from the action of a mitochondrial uncoupler
✍ Scribed by Anthony Collins; Maureen K. Larson
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 137 KB
- Volume
- 219
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
Abstract
We previously showed inhibition of K~ir~2 inward rectifier K^+^ channels expressed in Xenopus oocytes by the mitochondrial agents carbonyl cyanide p‐trifluoromethoxyphenylhydrazone (FCCP) and sodium azide. Mutagenesis studies suggested that FCCP may act via phosphatidylinositol 4,5‐bisphosphate (PIP~2~) depletion. This mechanism could be reversible in intact cells but not in excised membrane patches which preclude PIP~2~ regeneration. This prediction was tested by investigating the reversibility of the inhibition of K~ir~2.2 by FCCP in intact cells and excised patches. We also investigated the effect of FCCP on K~ir~2.2 expressed in human embryonic kidney (HEK) cells. K~ir~2.2 current, expressed in Xenopus oocytes, increased in inside‐out patches from FCCP‐treated and untreated oocytes. The fraction of total current that increased was 0.79 ± 0.05 in control and 0.89 ± 0.03 in 10 µM FCCP‐treated (P > .05). Following “run‐up,” K~ir~2.2 current was re‐inhibited by “cramming” inside‐out patches into oocytes. Therefore, run‐up reflected not reversal of inhibition by FCCP, but washout of an endogenous inhibitor. K~ir~2.2 current recovered in intact oocytes within 26.5 h of FCCP removal. Injection of oocytes with 0.1 U apyrase completely depleted ATP (P < .001) but did not inhibit K~ir~2.2 and inhibited K~ir~2.1 by 35% (P < .05). FCCP only partially reduced [ATP] (P < .001), despite inhibiting K~ir~2.2 by 75% (P < .01) but not K~ir~2.1. FCCP inhibited K~ir~2.2 expressed in HEK cells. The recovery of K~ir~2.2 from inhibition by FCCP requires intracellular components, but direct depletion of ATP does not reproduce the differential inhibitory effect of FCCP. Inhibition of K~ir~2.2 by FCCP is not unique to Xenopus oocytes. J. Cell. Physiol. 219: 8–13, 2009. © 2008 Wiley‐Liss, Inc.