Quantitation of aquaporin-2 abundance in microdissected collecting
ducts: axial distribution and control by avp.
Kishore, Bellamkonda K., James M. Terris, and Mark A. Knepper.
Laboratory of Kidney and Electrolyte Metabolism, National Heart,
Lung and Blood Institute, National Institutes of Health, and
Department of Physiology, Uniformed Services University of the Health
Sciences, Bethesda, Maryland
APStracts 3:0011F, 1996.
Aquaporin-2 (AQP2) is the vasopressin-regulated water channel of the
renal collecting ducts. Using an improved version of a fluorescence
-based ELISA (Maeda et al, 1995; JCI 95:422-428), we quantified AQP2
protein abundance in microdissected renal collecting ducts from
normal Sprague-Dawley (SD) rats and vasopressin-deficient Brattleboro
rats. Standard curves were linear in the range of 0-200 fmoles/well
and were highly reproducible from day-to-day (lower limit of
detection 2.3 fmoles; coefficient of variation 6-9%). In SD rats
thirst ed for 24?h, the measured quantities of AQP2 were (x109
molecules/mm): cortical collecting ducts (CCD), 4.3?+/-?0.5; outer
medullary collecting ducts (OMCD), 10.1?+/-?1.7; initial 1/3rd of
inner medullary collecting duct (IMCD-1), 9.2?+/-?1.1; middle 1/3rd
of the IMCD (IMCD-2), 7.5?+/-?0.8; terminal 1/3rd of the IMCD (IMCD
-3), 3.3?+/-?0.6; n?=?7-12. In IMCD-2 this corresponds to 11.8?+/-?1.3
x106 copies of AQP2 molecules per cell. Thus AQP2 is extremely
abundant in collecting duct cells. AQP2 levels were decreased in
untreated Brattleboro rats relative to the parent strain Long-Evans
(LE) by 68% in IMCD-2 and 44% in CCD. Follow ing vasopressin infusion
by osmotic minipumps, AQP2 levels in IMCD-2 of Brattleboro rats rose
gradually, reaching levels equivalent to those seen in LE rats after
5 days. A similar rise was seen in the CCD indicating that the
vasopressin-induced increase was not dependent on a large increase in
the interstitial tonicity. Thus, a rise in circulating vasopressin
concentration increases the level of AQP2 protein expression in
collecting ducts, presumably via a direct action of vasopressin.
Received 18 October 1995; accepted in final form 28 December
1995.
APS Manuscript Number F353-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96