Water transport in the collecting duct of japanese quail.
Nishimura, Hiroko, Chizuko Koseki, and Tarun B. Patel.
Department of Physiology and Biophysics, University of Tennessee,
Memphis, Memphis, TN 38163, National Cardiovascular Center Research
Institute, Osaka 565, Japan, and Department of Pharmacology,
University of Tennessee, Memphis, Memphis, TN 38163
APStracts 3:0209R, 1996.
Previously, we reported that the countercurrent urine concentration
mechanism in birds appears to operate by recycling of a single solute
(NaCl), in which the thick ascending limb of looped nephrons provides
an energy source. To determine the importance of the medullary
collecting duct (MCD) in the countercurrent multiplier system, we
examined in isolated and perfused MCDs from Japanese quail, Coturnix
coturnix, the osmotic and/or diffusional water permeability and
whether AVT regulates water permeability. We noted that dark cells
that possess electron-dense cytoplasma and numerous mitochondria and
light mucus-secreting cells exist in the cortical CD, whereas only
mucus-secreting cells are present in the MCDs. The volume flux (Jv)
in the MCDs from intact birds and that from the water-deprived birds
were nearly zero; after exposure to a hyperosmotic bath and AVT (2 x
10-5 M), the Jv was significantly higher in water-deprived birds. The
diffusional water permeability (Pdw) was moderately high in MCDs
bathed in an isosmotic bath in which the Pdw was increased slightly
by AVT (10-5 M, bath) and more markedly (10-5 M) by forskolin (FSK),
whereas 1,9-dideoxy FSK (an inactive analog) showed no effect.
Furthermore, the basal cAMP levels were higher in the medulla than in
the cortex and were stimulated only slightly by AVT (10-5 M) and
markedly by FSK (10-4 M) in both the cortex and medulla. These
results indicate in the Coturnix CD: 1) two types of cells are
present; while dark cells resemble mammalian intercalated cells
morphologically, it is not certain whether mucus-secreting cells are
equivalent to principal cells. 2) AVT increases Pdw via a cAMP
mechanism; the relatively high basal Pdw and minor effect of AVT on
Jv and Pdw suggest, however, that diffusional water movement across
the MCD may occur without significant direct control by AVT.
Received 16 January 1996; accepted in final form 20 May 1996.
APS Manuscript Number R19-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96