Developmental regulation of chloride/formate exchange in the guinea
pig proximal tubule.
Guillery, Edward N., and David J. Huss.
Department of Pediatrics, The University of Wisconsin, Madison, WI
53792-4108
APStracts 2:0088F, 1995.
There is a marked decrease in renal NaCl excretion immediately
following birth. To test the hypothesis that parallel upregulation of
the proximal tubule apical membrane Na+/H+ and Cl-/formate exchangers
contributes to this postnatal adaptation, we measured exchanger
activities in brush border membrane vesicles from near-term fetal, 3
-5 day-old and adult guinea pigs. Uptake of 36Cl- was measured in the
presence of an outwardly directed formate gradient and an inwardly
directed proton gradient. In other experiments, 22Na+ uptake was
measured in the presence of an outwardly directed proton gradient.
36Cl- uptake was inhibitable by DIDS and furosemide and 22Na+ uptake
was inhibitable by amiloride. Maximal uptakes of both 36Cl- and 22Na+
exceeded 2-hour equilibration values in vesicles from newborn and
adult guinea pigs, suggesting transporter mediated uptake. Such
overshoots were not seen with the vesicles from fetuses. Compared
with vesicles from fetuses, the initial velocity of formate-driven
36Cl- uptake was 73% greater in vesicles from newborns and 65%
greater in vesicles from adults. These results demonstrate parallel
upregulation of proximal tubule Na+/H+ and Cl-/formate exchanger
activities immediately after birth. This parallel upregulation may be
important in mediating the postnatal decrease in renal NaCl
excretion.
Received 29 December 1994; accepted in final form 16 May 1995.
APS Manuscript Number F465-4.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 26 May 1995.