Abstract
Chloroquine and related compounds can inhibit inwardly rectifying potassium channels by multiple potential mechanisms, including pore block and allosteric effects on channel gating. Motivated by reports that chloroquine inhibition of cardiac ATP-sensitive inward rectifier K+ current (IKATP) is antifibrillatory in rabbit ventricle, we investigated the mechanism of chloroquine inhibition of ATP-sensitive potassium (KATP) channels (Kir6.2/SUR2A) expressed in human embryonic kidney 293 cells, using inside-out patch-clamp recordings. We found that chloroquine inhibits the Kir6.2/SUR2A channel by interacting with at least two different sites and by two mechanisms of action. A fast-onset effect is observed at depolarized membrane voltages and enhanced by the N160D mutation in the central cavity, probably reflecting direct channel block resulting from the drug entering the channel pore from the cytoplasmic side. Conversely, a slow-onset, voltage-independent inhibition of IKATP is regulated by chloroquine interaction with a different site and probably involves disruption of interactions between Kir6.2/SUR2A and phosphatidylinositol 4,5-bisphosphate. Our findings reveal multiple mechanisms of KATP channel inhibition by chloroquine, highlighting the numerous convergent regulatory mechanisms of these ligand-dependent ion channels.
Footnotes
This work was supported by the National Institutes of Health National Heart, Lung, and Blood Institute [Grant R01 HL45742] (to C.G.N.); and Consejo Nacional de Ciencia y Tecnología–Secretaría de Educación Pública (México) [Grant CB-2008-01-105941] (to J.A.S.-C.). H.T.K. is supported by New Investigator awards from the Heart and Stroke Foundation of Canada and the Michael Smith Foundation for Health Research.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
ABBREVIATIONS:
- KATP
- ATP-sensitive potassium
- SUR
- sulfonylurea receptor
- PIP2
- phosphatidylinositol 4,5-bisphosphate
- IK1
- inward rectifier K+ current
- IKATP
- ATP-sensitive inward rectifier K+ current
- IKACh
- K+ current activated by muscarinic agonist
- HEK
- human embryonic kidney
- WT
- wild-type
- CAD
- cationic amphiphilic drug.
- Received April 5, 2012.
- Accepted July 31, 2012.
- Copyright © 2012 The American Society for Pharmacology and Experimental Therapeutics
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