Synergistic interaction and the role of C-terminus in the activation of TRAAK K+ channels by pressure, free fatty acids and alkali.
TRAAK is a member of the tandem-pore K+ channel family, and is expressed mainly in the brain. Using rat TRAAK (rTRAAK), we studied its single-channel kinetics, interactive modes of activation, and the role of the C-terminus on its pressure-, fatty-acid- and pH-sensitivity. When expressed in COS-7 cells, rTRAAK showed a mildly inwardly rectifying single-channel current/voltage relationship in symmetrical 140 mM KCl. Unlike TREK-1 and TREK-2, which are activated by acidic conditions, rTRAAK was activated by alkali conditions, such that a change in intracellular pH from 7.3 to 8.3 and 8.8 increased channel activity 5- and 14-fold, respectively. Pressure and alkali produced a strong synergistic activation, and pressure and arachidonic acid (AA) produced a mild synergistic activation. The only additive effect was observed with alkali and AA. Replacing the C-terminus of rTRAAK with that of TASK-1 or TASK-3 did not affect the response to pressure, AA or alkali. In contrast, replacing the C-terminus of TREK-2 with that of TASK-3 abolished the sensitivity to AA and acid, but not to pressure. These results show that rTRAAK is an alkali-sensing K+ channel that shows synergistic activation with pressure, and that the mechanism of activation of rTRAAK and TREK by free fatty acids are different.
Kim
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Y
Department of Physiology and Biophysics, Finch University of Health Sciences, Chicago Medical School, 3333 Green Bay Road, North Chicago, IL 60064, USA.
Bang
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H
Gnatenco
C
C
Kim
D
D
D000595:Amino Acid Sequence; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D015152:Blotting, Northern; D019556:COS Cells; D002478:Cells, Cultured; D005230:Fatty Acids, Nonesterified / Q000494:pharmacology*; D015870:Gene Expression; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D011312:Pressure; D051381:Rats; D011994:Recombinant Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection
D005230:Fatty Acids, Nonesterified; C503434:Kcnk4 protein, rat; D015221:Potassium Channels; D011994:Recombinant Proteins; D016718:Arachidonic Acid