Na(+)-induced inward rectification in the two-pore domain K(+) channel, TASK-2.
TASK-2 is a member of the two-pore domain K(+) (K(2P)) channel family that is expressed at high levels in several epithelia, including the proximal tubule. In common with the other TASK channels, TASK-2 is sensitive to changes in extracellular pH. We have expressed human TASK-2 in Chinese hamster ovary cells and studied whole cell and single-channel activity by patch clamp. The open probability of K(2P) channels is generally independent of voltage, yielding linear current-voltage (I-V) curves. Despite these properties, we found that these channels showed distinct inward rectification immediately on the establishment of whole cell clamp, which became progressively less pronounced with time. This rectification was due to intracellular Na(+) but was unaffected by polyamines or Mg(2+) (agents that cause rectification in Kir channels). Rectification was concentration- and voltage-dependent and could be reversibly induced by switching between Na(+)-rich and Na(+)-free bath solutions. In excised inside-out patches, Na(+) reduced the amplitude of single-channel currents, indicative of rapid block and unblock of the pore. Mutations in the selectivity filter abolished Na(+)-induced rectification, suggesting that Na(+) binds within the selectivity filter in wild-type channels. This sensitivity to intracellular Na(+) may be an additional potential regulatory mechanism of TASK-2 channels.
School of Biomedical Sciences, University of Leeds, Leeds, UK.
Michael J
MJ
Morton
Sarah
S
Chipperfield
Abdulrahman
A
Abohamed
Asipu
A
Sivaprasadarao
Malcolm
M
Hunter
D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000502:physiology; D006224:Cricetinae; D003412:Cricetulus; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D009154:Mutation; D011073:Polyamines / Q000494:pharmacology; D024683:Potassium Channels, Tandem Pore Domain / Q000235:genetics / Q000502:physiology*; D012964:Sodium / Q000502:physiology*; D014162:Transfection
C498739:Kcnk5 protein, mouse; D011073:Polyamines; D024683:Potassium Channels, Tandem Pore Domain; D012964:Sodium; D008274:Magnesium