Effects of mineralocorticoid and K+ concentration on K+ secretion and ROMK channel expression in a mouse cortical collecting duct cell line.
The cortical collecting duct (CCD) plays a key role in regulated K(+) secretion, which is mediated mainly through renal outer medullary K(+) (ROMK) channels located in the apical membrane. However, the mechanisms of the regulation of urinary K(+) excretion with regard to K(+) balance are not well known. We took advantage of a recently established mouse CCD cell line (mCCD(cl1)) to investigate the regulation of K(+) secretion by mineralocorticoid and K(+) concentration. We show that this cell line expresses ROMK mRNA and a barium-sensitive K(+) conductance in its apical membrane. As this conductance is sensitive to tertiapin-Q, with an apparent affinity of 6 nM, and to intracellular acidification, it is probably mediated by ROMK. Overnight exposure to 100 nM aldosterone did not significantly change the K(+) conductance, while it increased the amiloride-sensitive Na(+) transport. Overnight exposure to a high K(+) (7 mM) concentration produced a small but significant increase in the apical membrane barium-sensitive K(+) conductance. The mRNA levels of all ROMK isoforms measured by qRT-PCR were not changed by altering the basolateral K(+) concentration but were decreased by 15-45% upon treatment with aldosterone (0.3 or 300 nM for 1 and 3 h). The paradoxical response of ROMK expression to aldosterone could possibly work as a preventative mechanism to avoid excessive K(+) loss which would otherwise result from the increased electrogenic Na(+) transport and associated depolarization of the apical membrane in the CCD. In conclusion, mCCD(cl1) cells demonstrate a significant K(+) secretion, probably mediated by ROMK, which is not stimulated by aldosterone but increased by overnight exposure to a high K(+) concentration.
Fodstad
Heidi
H
Department of Pharmacology and Toxicology, University of Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland. heidi.fodstad@unil.ch
Gonzalez-Rodriguez
Elena
E
Bron
Sylvian
S
Gaeggeler
Hanspeter
H
Guisan
Barbara
B
Rossier
Bernard C
BC
Horisberger
Jean-Daniel
JD
D000595:Amino Acid Sequence; D000818:Animals; D001464:Barium / Q000493:pharmacokinetics; D001514:Bee Venoms / Q000494:pharmacology; D002460:Cell Line; D016764:Cell Polarity / Q000502:physiology; D003470:Culture Media / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D007536:Isomerism; D007672:Kidney Cortex / Q000166:cytology / Q000502:physiology; D007685:Kidney Tubules, Collecting / Q000166:cytology* / Q000502:physiology*; D051379:Mice; D008901:Mineralocorticoids / Q000378:metabolism*; D008969:Molecular Sequence Data; D011188:Potassium / Q000493:pharmacokinetics*; D024661:Potassium Channels, Inwardly Rectifying / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism
D001514:Bee Venoms; D003470:Culture Media; C510693:Kcnj1 protein, mouse; D008901:Mineralocorticoids; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger; D001464:Barium; C029738:tertiapin; D011188:Potassium