Mechanisms of stimulation of proximal tubule chloride transport by
formate and oxalate.
Wang, Tong, Allan L. Egbert, Jr., Thecla Abbiati, Peter S. Aronson,
and Gerhard Giebisch.
Departments of Cellular and Molecular Physiology, and Internal
Medicine, Yale University School of Medicine, New Haven, CT 06520
-8026
APStracts 3:0081F, 1996.
We have previously demonstrated that formate and oxalate stimulate
volume absorption in the rat proximal tubule, consistent with Cl-
-formate and Cl--oxalate exchange processes across the apical
membrane. To sustain Cl- absorption by these processes requires
mechanisms for recycling formate and oxalate from lumen to cell. The
aims of the present study were to characterize these mechanisms of
formate and oxalate recycling. Proximal tubules and peritubular
capillaries were simultaneously microperfused in the rat kidney in
situ. Serum formate concentration was determined to be 56.5 +/- 7.7
[mu]M. Addition of 5, 50 and 500 [mu]M formate to both luminal and
capillary perfusates significantly increased net Cl- absorption (JCl)
by 26%, 26% and 46%, respectively. JCl was stimulated 38% by 1 [mu]M
oxalate added to the perfusate. Removal of sulfate completely
prevented the stimulation of JCl by 1 [mu]M oxalate but had no effect
on the stimulation of JCl by formate. Luminal addition of the Na+-H+
exchange inhibitor EIPA completely blocked the stimulation of JCl by
50 [mu]M formate but had no effect on stimulation by oxalate. We
conclude that physiologic concentrations of formate and oxalate
markedly stimulate Cl- and fluid absorption in the rat proximal
convoluted tubule. Whereas formate recycling most likely involves
Na+-H+ exchange in parallel with H+-coupled formate entry, oxalate
recycling involves sodium-sulfate cotransport in parallel with
sulfate-oxalate exchange.
Received 29 January 1996; accepted in final form 11 April 1996.
APS Manuscript Number F30-6.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 May 96