Modulation of the two-pore domain acid-sensitive K+ channel TASK-2 (KCNK5) by changes in cell volume.
The molecular identity of K(+) channels involved in Ehrlich cell volume regulation is unknown. A background K(+) conductance is activated by cell swelling and is also modulated by extracellular pH. These characteristics are most similar to those of newly emerging TASK (TWIK-related acid-sensitive K(+) channels)-type of two pore-domain K(+) channels. mTASK-2, but not TASK-1 or -3, is present in Ehrlich cells and mouse kidney tissue from where the full coding sequences were obtained. Heterologous expression of mTASK-2 cDNA in HEK-293 cells generated K(+) currents in the absence intracellular Ca(2+). Exposure to hypotonicity enhanced mTASK-2 currents and osmotic cell shrinkage led to inhibition. This occurred without altering voltage dependence and with only slight decrease in pK(a) in hypotonicity but no change in hypertonicity. Replacement with other cations yields a permselectivity sequence for mTASK-2 of K(+) > Rb(+) Cs(+) > NH(4)(+) > Na(+) congruent with Li(+), similar to that for the native conductance (I(K, vol)). Clofilium, a quaternary ammonium blocker of I(K, vol), blocked the mTASK-2-mediated K(+) current with an IC(50) of 25 microm. The presence of mTASK-2 in Ehrlich cells, its functional similarities with I(K, vol), and its modulation by changes in cell volume suggest that this two-pore domain K(+) channel participates in the regulatory volume decrease phenomenon.
Niemeyer
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MI
Centro de Estudios Cientificos, Av. Arturo Prat 514, Casilla 1469, Valdivia, Chile. miniemeyer@cecs.cl
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Barros
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D000818:Animals; D015152:Blotting, Northern; D002286:Carcinoma, Ehrlich Tumor; D002412:Cations; D002460:Cell Line; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D007668:Kidney / Q000378:metabolism; D051379:Mice; D016133:Polymerase Chain Reaction; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism*; D024683:Potassium Channels, Tandem Pore Domain; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
D002412:Cations; D018076:DNA, Complementary; C410295:KCNK5 protein, human; C498739:Kcnk5 protein, mouse; D015221:Potassium Channels; D024683:Potassium Channels, Tandem Pore Domain; D000644:Quaternary Ammonium Compounds; D012333:RNA, Messenger; D012313:RNA; C022799:clofilium; D011188:Potassium