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).
↵
This article has supplemental material available at molpharm.aspetjournals.org.
- Copyright © 2017 by The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|
