Inhibition of a background potassium channel by Gq protein alpha-subunits.
Two-pore-domain K(+) channels provide neuronal background currents that establish resting membrane potential and input resistance; their modulation provides a prevalent mechanism for regulating cellular excitability. The so-called TASK channel subunits (TASK-1 and TASK-3) are widely expressed, and they are robustly inhibited by receptors that signal through Galphaq family proteins. Here, we manipulated G protein expression and membrane phosphatidylinositol 4,5-bisphosphate (PIP(2)) levels in intact and cell-free systems to provide electrophysiological and biochemical evidence that inhibition of TASK channels by Galphaq-linked receptors proceeds unabated in the absence of phospholipase C (PLC) activity, and instead involves association of activated Galphaq subunits with the channels. Receptor-mediated inhibition of TASK channels was faster and less sensitive to a PLCbeta1-ct minigene construct than inhibition of PIP(2)-sensitive Kir3.4(S143T) homomeric channels that is known to be dependent on PLC. TASK channels were strongly inhibited by constitutively active Galphaq, even by a mutated version that is deficient in PLC activation. Receptor-mediated TASK channel inhibition required exogenous Galphaq expression in fibroblasts derived from Galphaq/11 knockout mice, but proceeded unabated in a cell line in which PIP(2) levels were reduced by regulated overexpression of a lipid phosphatase. Direct application of activated Galphaq, but not other G protein subunits, inhibited TASK channels in excised patches, and constitutively active Galphaq subunits were selectively coimmunoprecipitated with TASK channels. These data indicate that receptor-mediated TASK channel inhibition is independent of PIP(2) depletion, and they suggest a mechanism whereby channel modulation by Galphaq occurs through direct interaction with the ion channel or a closely associated intermediary.
Department of Pharmacology, University of Virginia, Charlottesville, 22908, USA.
Xiangdong
X
Chen
Edmund M
EM
Talley
Nitin
N
Patel
Ana
A
Gomis
William E
WE
McIntire
Biwei
B
Dong
Félix
F
Viana
James C
JC
Garrison
Douglas A
DA
Bayliss
D000818:Animals; D002460:Cell Line; D002474:Cell-Free System; D004594:Electrophysiology; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D018408:Patch-Clamp Techniques; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D024683:Potassium Channels, Tandem Pore Domain / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D051381:Rats; D018411:Spodoptera; D010738:Type C Phospholipases / Q000378:metabolism
D019269:Phosphatidylinositol 4,5-Diphosphate; D024683:Potassium Channels, Tandem Pore Domain; D021122:Protein Subunits; D010738:Type C Phospholipases; D043802:GTP-Binding Protein alpha Subunits, Gq-G11