Developmental changes in rabbit juxtamedullary proximal convoluted
tubule water permeability.
Quigley, Raymond, and Michel Baum.
Departments of Pediatrics1 and Internal Medicine, University of
Texas Southwestern Medical Center, Dallas, Texas 75235-9063
APStracts 3:0136F, 1996.
The mammalian proximal tubule reabsorbs the bulk of the glomerular
filtrate in a nearly isosmotic fashion due to the high osmotic water
permeability (Pf) of this segment. While the characteristics of
proximal tubule water transport have been studied in the adult
proximal tubule, little is known about the neonatal segment. The
present study directly measured the Pf and diffusional water
permeability (PDw) of neonatal (102 day old) and adult rabbit
juxtamedullary proximal convoluted tubules (PCT) using in vitro
microperfusion. The Pf of neonatal juxtamedullary PCT was greater
than the Pf of adult juxtamedullary PCT. In contrast, the PDw was not
different between the two groups. The Pf and PDw of both neonatal and
adult tubules were inhibited to the same degree by p
-chloromercuribenzene sulfonate (pCMBS) and had identical activation
energies. The transepithelial reflection coefficients of NaCl and
NaHCO3 were also found to be similar in both the neonatal and adult
proximal tubules. Thus, neonatal and adult juxtamedullary PCT have
many characteristics of water transport that are identical, however,
neonatal Pf is three to five times that of the adult value. This
difference in Pf with identical PDw values may give an insight into
the transepithelial pathway for water movement in the neonatal
tubule.
Received 23 October 1995; accepted in final form 10 July 1996.
APS Manuscript Number F359-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 August 1996