TBAK-1 and TASK-1, two-pore K(+) channel subunits: kinetic properties and expression in rat heart.
A mammalian K(+) channel subunit (TBAK-1/TASK-1) containing two pore domains and four transmembrane segments and whose mRNA is highly expressed in the heart has been cloned recently. TBAK-1 and TASK-1 are identical except for the additional nine amino acids in the NH(2) terminus of TBAK-1. We examined their kinetic properties, pH sensitivity, and regional cardiac mRNA expression and determined whether a native cardiac K(+) channel with similar kinetic properties was present. When TBAK-1 or TASK-1 was transiently expressed in COS-7 cells, time- and voltage-independent whole cell currents were observed. Single-channel conductances of TBAK-1 and TASK-1 were 14.6 +/- 1.0 and 13.8 +/- 2.8 pS, respectively, at -80 mV in 140 mM extracellular K(+), and the mean open times were 0.8 +/- 0.1 and 0.6 +/- 0.1 ms, respectively. Both TBAK-1 and TASK-1 were highly sensitive to extracellular pH such that a decrease from 7.2 to 6.4 reduced their open probability (P(o)) by 81 +/- 14% and 80 +/- 16%, whereas a decrease in intracellular pH from 7.2 to 6.4 reduced the P(o) by 42 +/- 10% and 47 +/- 12%, respectively. TBAK-1/TASK-1 mRNA was expressed in all regions of the rat heart, with the highest level of expression in the right atrium. A 14-pS K(+) channel with kinetic properties similar to those of TBAK-1/TASK-1 was identified in rat atrial and ventricular cells. These results indicate that TBAK-1/TASK-1 represents a functional native K(+) channel in the rat heart.
Kim
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Department of Physiology, Chicago Medical School, Finch University of Health Sciences, North Chicago, Illinois 60064, USA.
Bang
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Kim
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D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D019556:COS Cells; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009419:Nerve Tissue Proteins; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D024683:Potassium Channels, Tandem Pore Domain; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats
D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D024683:Potassium Channels, Tandem Pore Domain; D012333:RNA, Messenger; C420132:potassium channel subfamily K member 3