Urea inhibits nak2cl cotransport in medullary thick ascending limb
cells.
Kaji, Deepak M., J. Diaz, and John C Parker.
Renal Section, Department of Medicine, Veterans Affairs Medical
Center, Bronx, New York, 10468 and Mount Sinai School of Medicine,
New York, NY 10029; and University of North Carolina at Chapel Hill,
Chapel Hill, NC 27599
APStracts 3:0308C, 1996.
We examined the effect of physiological concentrations of urea (100
-500 mM) on NaK2Cl cotransport in cultured cells from mouse medullary
thick ascending limb (mTAL). Urea acutely inhibited bumetanide
-sensitive K influx in mTAL cells in a concentration dependent
fashion, with a statistically significant inhibition (19%) at 100 mM,
and 86% inhibition at 500 mM. The effect of urea was entirely
reversible, and was blocked by prior treatment with okadaic acid, a
phosphatase inhibitor, suggesting that urea exerts its action
upstream of the phosphorylation-dephosphorylation step. Cell volume
was unchanged in the presence of 500 mM urea. The number of [3H]
bumetanide binding sites, a measure of the number of functioning
cotransporter sites, was decreased in the presence of urea, and the
decrease in bumetanide binding was proportional to the decrease in
bumetanide-sensitive K influx. Urea also stimulated the Ba-sensitive,
swelling-activated K efflux from mTAL cells. Thus, urea, in
concentrations that prevail in the renal medulla, alters ion
transport in mTAL cells.
Received 22 January 1996; accepted in final form 12 September
1996.
APS Manuscript Number C40-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996