Document Detail


Diluting segment in kidney of dogfish shark. I. Localization and characterization of chloride absorption.
MedLine Citation:
PMID:  2155546     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Single tubules, dissected from the peritubular sheath of the dorsal bundle zone of kidney of the dogfish shark, Squalus acanthias, were perfused in vitro at 17-18 degrees C. This segment is the largest of the five in the peritubular sheath and had average inner and outer diameters of 46.9 +/- 1.2 and 74.4 +/- 2.1 microns, respectively (n = 32). These values suggest that this is the intermediate IV segment. When perfused with symmetrical buffered elasmobranch saline, intermediate IV segments exhibited high rates of Cl- absorption (JCl, pmol.s-1.cm-2): 1,696 at an average perfusion rate (Vo) of 8.2 nl/min. Cl- absorption was highly flow dependent [1/JCl = 57.95(1/Vo) + 1.75; r = 0.71, P less than 0.01]. Maximal rates of Cl-absorption, calculated from reciprocal transformation of the flow dependence of JCl, yielded a value of 5,714 pmol.s-1.cm-2. In the presence of a 200-mosmol/kg transepithelial osmotic gradient, fluid absorption was negligible. The spontaneous transepithelial voltage (Vte, mucosal with respect to serosal compartment) averaged 8.0 +/- 1.0 mV (n = 26). Such active transport of Cl- in the absence of fluid movement and in the presence of a lumen-positive transepithelial voltage is characteristic of amphibian and mammalian diluting segments. Na(+)-to-Cl- permeability ratios (PNa/PCl) averaged 2.5 +/- 0.5, indicating that, as in mammalian thick ascending limbs, this segment is Na+ (cation) permselective. Vte was dependent on the presence of Na+ and Cl- in the external solutions and was reversibly abolished by isosmotic replacement with N-methyl-D-glucamine or with isethionate, respectively. Ouabain inhibited Vte but was not reversible within the time course of these experiments. Furosemide (10(-4) M), but not equimolar concentrations of amiloride or hydrochlorothiazide, added to the luminal perfusate inhibited both Vte and JCl. These results suggest that apical membrane Na+ entry in intermediate IV segments is mediated by Na(+)-K(+)-Cl- cotransport and is consistent with the existence of a functional role of urinary dilution in the reabsorption of urea in the elasmobranch kidney.
Authors:
P A Friedman; S C Hebert
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Publication Detail:
Type:  In Vitro; Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  The American journal of physiology     Volume:  258     ISSN:  0002-9513     ISO Abbreviation:  Am. J. Physiol.     Publication Date:  1990 Feb 
Date Detail:
Created Date:  1990-04-03     Completed Date:  1990-04-03     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0370511     Medline TA:  Am J Physiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  R398-408     Citation Subset:  IM    
Affiliation:
Mt. Desert Island Biological Laboratory, Salsbury Cove, Maine 04672.
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MeSH Terms
Descriptor/Qualifier:
Absorption
Animals
Body Fluids / metabolism
Chlorides / metabolism*
Cyclic AMP / pharmacology
Diuretics / pharmacology
Dogfish / metabolism*
Electrophysiology
Kidney Tubules / anatomy & histology,  metabolism*,  physiology
Osmosis
Ouabain / pharmacology
Permeability
Sharks / metabolism*
Tissue Distribution
Water / metabolism
Chemical
Reg. No./Substance:
0/Chlorides; 0/Diuretics; 60-92-4/Cyclic AMP; 630-60-4/Ouabain; 7732-18-5/Water

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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