Separate regulation of na+ and anion transport by rat imcd:
location, aldosterone, hypertonicity, tgf-[beta]1, and camp.
Husted, Russell F., and John B. Stokes.
Laboratory of Epithelial Transport, Department of Internal
Medicine, University of Iowa College of Medicine and Department of
Veterans Affairs Medical Center, Iowa City, Iowa 52242
APStracts 3:0070F, 1996.
We have investigated some of the factors known or suspected to
influence ion transport by the rat inner medullary collecting duct
and have analyzed their actions on active Na+ absorption and active
anion secretion by primary cultures. Cells from the terminal 1-2 mm
(tip) of the papilla had a lower basal rate of Na+ absorption (2.0
[mu]A/cm2) than cells from the more proximal portions (6.5
[mu]A/cm2). Aldosterone increased Na+ transport 7 fold in the tip
cells and 3 fold in the proximal cells. The magnitude of anion
secretion in response to cAMP agonists was similar in the 2 regions
and was unaffected by aldosterone. The morphology of monolayers from
both regions was also similar. In monolayers cultured from the entire
inner medulla, hypertonic (100 mOsm) urea, NaCl, or sucrose reduced
Na+ transport but had no significant effect on anion secretion. TGF
-[beta]1, known to blunt the effect of steroids on Na+ transport, had
no effect on anion secretion. Finally, cAMP had no effect on Na+
transport, a result that contrasts with its effect on Na+ transport
by other epithelial cells demonstrating steroid-responsive,
electrogenic Na+ transport. These results demonstrate some potential
differences in the magnitude of Na+ transport by position along the
inner medulla. They further demonstrate separate regulation of Na+
and anion transport.
Received 28 August 1995; accepted in final form 27 March 1996.
APS Manuscript Number F286-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96