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Diluting segment in kidney of dogfish shark. I. Localization and characterization of chloride absorption.
Am J Physiol. 1990 Feb; 258(2 Pt 2):R398-408.AJ

Abstract

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+Show Affiliations

Mt. Desert Island Biological Laboratory, Salsbury Cove, Maine 04672.No affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

Language

eng

PubMed ID

2155546

Citation

Friedman, P A., and S C. Hebert. "Diluting Segment in Kidney of Dogfish Shark. I. Localization and Characterization of Chloride Absorption." The American Journal of Physiology, vol. 258, no. 2 Pt 2, 1990, pp. R398-408.
Friedman PA, Hebert SC. Diluting segment in kidney of dogfish shark. I. Localization and characterization of chloride absorption. Am J Physiol. 1990;258(2 Pt 2):R398-408.
Friedman, P. A., & Hebert, S. C. (1990). Diluting segment in kidney of dogfish shark. I. Localization and characterization of chloride absorption. The American Journal of Physiology, 258(2 Pt 2), R398-408.
Friedman PA, Hebert SC. Diluting Segment in Kidney of Dogfish Shark. I. Localization and Characterization of Chloride Absorption. Am J Physiol. 1990;258(2 Pt 2):R398-408. PubMed PMID: 2155546.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Diluting segment in kidney of dogfish shark. I. Localization and characterization of chloride absorption. AU - Friedman,P A, AU - Hebert,S C, PY - 1990/2/1/pubmed PY - 1990/2/1/medline PY - 1990/2/1/entrez SP - R398 EP - 408 JF - The American journal of physiology JO - Am. J. Physiol. VL - 258 IS - 2 Pt 2 N2 - 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. SN - 0002-9513 UR - https://www.unboundmedicine.com/medline/citation/2155546/Diluting_segment_in_kidney_of_dogfish_shark__I__Localization_and_characterization_of_chloride_absorption_ L2 - http://journals.physiology.org/doi/full/10.1152/ajpregu.1990.258.2.R398?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub=pubmed DB - PRIME DP - Unbound Medicine ER -