Article: article from journal or magazin.
Effects of mineralocorticoid and K+ concentration on K+ secretion and ROMK channel expression in a mouse cortical collecting duct cell line.
American Journal of Physiology. Renal Physiology
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.
Amino Acid Sequence, Animals, Barium/pharmacokinetics, Bee Venoms/pharmacology, Cell Line, Cell Polarity/physiology, Culture Media/pharmacology, Dose-Response Relationship, Drug, Gene Expression/drug effects, Gene Expression/physiology, Isomerism, Kidney Cortex/cytology, Kidney Cortex/physiology, Kidney Tubules, Collecting/cytology, Kidney Tubules, Collecting/physiology, Mice, Mineralocorticoids/metabolism, Molecular Sequence Data, Potassium/pharmacokinetics, Potassium Channels, Inwardly Rectifying/chemistry, Potassium Channels, Inwardly Rectifying/genetics, RNA, Messenger/metabolism
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