Abstract
The TWIK-related acid-sensitive potassium channel 3 (TASK-3; KCNK9) tandem pore potassium channel function is activated by halogenated anesthetics through binding at a putative anesthetic-binding cavity. To understand the pharmacologic requirements for TASK-3 activation, we studied the concentration–response of TASK-3 to several anesthetics (isoflurane, desflurane, sevoflurane, halothane, α-chloralose, 2,2,2-trichloroethanol [TCE], and chloral hydrate), to ethanol, and to a panel of halogenated methanes and alcohols. We used mutagenesis to probe the anesthetic-binding cavity as observed in a TASK-3 homology model. TASK-3 activation was quantified by Ussing chamber voltage clamp analysis. We mutagenized the residue Val-136, which lines the anesthetic-binding cavity, its flanking residues (132 to 140), and Leu-122, a pore-gating residue. The 2-halogenated ethanols activate wild-type TASK-3 with the following rank order efficacy (normalized current [95% confidence interval]): 2,2,2-tribromo-(267% [240–294]) > 2,2,2-trichloro-(215% [196–234]) > chloral hydrate (165% [161–176]) > 2,2-dichloro- > 2-chloro ≈ 2,2,2-trifluoroethanol > ethanol. Similarly, carbon tetrabromide (296% [245–346]), carbon tetrachloride (180% [163–196]), and 1,1,1,3,3,3-hexafluoropropanol (200% [194–206]) activate TASK-3, whereas the larger carbon tetraiodide and α-chloralose inhibit. Clinical agents activate TASK-3 with the following rank order efficacy: halothane (207% [202–212]) > isoflurane (169% [161–176]) > sevoflurane (164% [150–177]) > desflurane (119% [109–129]). Mutations at and near residue-136 modify TCE activation of TASK-3, and interestingly M159W, V136E, and L122D were resistant to both isoflurane and TCE activation. TASK-3 function is activated by a multiple agents and requires a halogenated substituent between ∼30 and 232 cm3/mol volume with potency increased by halogen polarizeability. Val-136 and adjacent residues may mediate anesthetic binding and stabilize an open state regulated by pore residue Leu-122. Isoflurane and TCE likely share commonalities in their mechanism of TASK-3 activation.
Footnotes
- Received January 7, 2017.
- Accepted March 20, 2017.
This research was supported the Massachusetts General Hospital Department of Anesthesia, Critical Care & Pain Medicine; the National Institutes of Health National Heart Lung and Blood Institute [Grant R01HL117871]; and Kantonsspital Aarau, Aarau, Switzerland (1410.000.062).
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- Copyright © 2017 by The American Society for Pharmacology and Experimental Therapeutics
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