Na(+) sensitivity of ROMK1 K(+) channel: role of the Na(+)/H(+) antiporter.
To examine the extracellular Na(+) sensitivity of a renal inwardly rectifying K(+) channel, we performed electrophysiological experiments on Xenopus oocytes or a human kidney cell line, HEK293, in which we had expressed the cloned renal K(+) channel, ROMK1 (Kir1. 1). When extracellular Na(+) was removed, the whole-cell ROMK1 currents were markedly suppressed in both the oocytes and HEK293 cells. Single-channel ROMK1 activities recorded in the cell-attached patch on the oocyte were not affected by removal of Na(+) from the pipette solution. However, macro-patch ROMK1 currents recorded on the oocyte were significantly suppressed by Na(+) removal from the bath solution. A blocker of Na(+)/H(+) antiporters, amiloride, largely inhibited the Na(+) removal-induced suppression of whole-cell ROMK1 currents in the oocytes. The pH-insensitive K80M mutant of ROMK1 was much less sensitive to Na(+) removal. Na(+) removal was found to induce a significant decrease in intracellular pH in the oocytes using H(+)-selective microelectrodes. Coexpression of ROMK1 with NHE3, which is a Na(+)/H(+) antiporter isoform of the kidney apical membrane, conferred increased sensitivity of ROMK1 channels to extracellular Na(+) in both the oocytes and HEK293 cells. Thus, it is concluded that the ROMK1 channel is regulated indirectly by extracellular Na(+), and that the interaction between NHE transporter and ROMK1 channel appears to be involved in the mechanism of Na(+) sensitivity of ROMK1 channel via regulating intracellular pH.
Sabirov
R Z
RZ
Department of Cellular and Molecular Physiology, National Institute for Physiological Sciences, Okazaki 444-8585, Japan.
Azimov
R R
RR
Ando-Akatsuka
Y
Y
Miyoshi
T
T
Okada
Y
Y
D000818:Animals; D002460:Cell Line; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D014981:Xenopus
C086989:KCNJ1 protein, human; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011994:Recombinant Proteins; D017923:Sodium-Hydrogen Exchangers; D012964:Sodium