Separate gating mechanisms mediate the regulation of K2P potassium channel TASK-2 by intra- and extracellular pH.
TASK-2 (KCNK5 or K(2P)5.1) is a background K(+) channel that is opened by extracellular alkalinization and plays a role in renal bicarbonate reabsorption and central chemoreception. Here, we demonstrate that in addition to its regulation by extracellular protons (pH(o)) TASK-2 is gated open by intracellular alkalinization. The following pieces of evidence suggest that the gating process controlled by intracellular pH (pH(i)) is independent from that under the command of pH(o). It was not possible to overcome closure by extracellular acidification by means of intracellular alkalinization. The mutant TASK-2-R224A that lacks sensitivity to pH(o) had normal pH(i)-dependent gating. Increasing extracellular K(+) concentration acid shifts pH(o) activity curve of TASK-2 yet did not affect pH(i) gating of TASK-2. pH(o) modulation of TASK-2 is voltage-dependent, whereas pH(i) gating was not altered by membrane potential. These results suggest that pH(o), which controls a selectivity filter external gate, and pH(i) act at different gating processes to open and close TASK-2 channels. We speculate that pH(i) regulates an inner gate. We demonstrate that neutralization of a lysine residue (Lys(245)) located at the C-terminal end of transmembrane domain 4 by mutation to alanine abolishes gating by pH(i). We postulate that this lysine acts as an intracellular pH sensor as its mutation to histidine acid-shifts the pH(i)-dependence curve of TASK-2 as expected from its lower pK(a). We conclude that intracellular pH, together with pH(o), is a critical determinant of TASK-2 activity and therefore of its physiological function.
Niemeyer
María Isabel
MI
Centro de Estudios Científicos, Valdivia 5110566, Chile. miniemeyer@cecs.cl
Cid
L Pablo
LP
Peña-Münzenmayer
Gaspar
G
Sepúlveda
Francisco V
FV
D000595:Amino Acid Sequence; D000818:Animals; D004594:Electrophysiology / Q000379:methods; D005786:Gene Expression Regulation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007684:Kidney Tubules / Q000378:metabolism*; D008239:Lysine / Q000737:chemistry; D051379:Mice; D008954:Models, Biological; D008969:Molecular Sequence Data; D011188:Potassium / Q000737:chemistry; D024683:Potassium Channels, Tandem Pore Domain / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013431:Sulfates / Q000737:chemistry
C498739:Kcnk5 protein, mouse; D024683:Potassium Channels, Tandem Pore Domain; D013431:Sulfates; D008239:Lysine; D011188:Potassium