Determinants of pH sensing in the two-pore domain K(+) channels TASK-1 and -2.
TASK-1 and -2 are members of the two-pore domain potassium (K(+)) channel family and are sensitive to changes in extracellular pH. The effects of mutating charged, extracellular-facing residues in TASK-1 and -2 were studied in Xenopusoocytes by two-electrode voltage clamp. Hydrogen ion block was independent of voltage with K(d) values of 149+/-17.9 nM [H(+)] ( n=6) and 5.76+/-1.23 nM [H(+)] ( n=7) for TASK-1 and -2, respectively. Compared to wild-type TASK-1, H72N, H98N, H98D and K210N displayed significant shifts in their K(d) values for hydrogen ion block ([H(+)]; 110+/-9.80 nM, 737+/-170 nM, 321+/-85.9 nM and 267+/-9.92 nM, respectively, n=6 each, P<0.05). Although significantly reducing its pH sensitivity, mutation of H98 in TASK-1 did not abolish pH sensitivity; this implies that H98 is not the only residue or domain involved in pH sensing of TASK-1. TASK-2 does not possess a histidine residue at the homologous position. However, the inclusion of such a residue failed to produce the expected increase in pH sensitivity; instead, a slight decrease was observed. Despite their structural homology and common sensitivity to pH, the TASK family of K(+) channels apparently has diverse pH-sensing mechanisms.
Morton
Michael J
MJ
School of Biomedical Sciences, Worsley Building, University of Leeds, Leeds LS2 9NQ, UK.
O'Connell
Anthony D
AD
Sivaprasadarao
Asipu
A
Hunter
Malcolm
M
D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D015374:Biosensing Techniques; D004553:Electric Conductivity; D004594:Electrophysiology; D005110:Extracellular Space / Q000378:metabolism; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D009865:Oocytes; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D024683:Potassium Channels, Tandem Pore Domain; D017434:Protein Structure, Tertiary / Q000502:physiology; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
C410295:KCNK5 protein, human; C498739:Kcnk5 protein, mouse; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D024683:Potassium Channels, Tandem Pore Domain; C420132:potassium channel subfamily K member 3