Adaptability of marine teleost renal inorganic sulfate excretion: evidence for glucocorticoid involvement

1989 ◽  
Vol 257 (3) ◽  
pp. R511-R516 ◽  
Author(s):  
J. L. Renfro
Keyword(s):  
Culture Medium ◽  
Brush Border Membrane ◽  
Renal Tubule ◽  
Membrane Vesicles ◽  
Renal Tubules ◽  
Pseudopleuronectes Americanus ◽  
Monolayer Cultures ◽  
Primary Monolayer ◽  
Primary Monolayer Cultures ◽  
Inorganic Sulfate

The marine winter flounder, Pseudopleuronectes americanus, ingests seawater (SW) and excretes most of the resultant divalent ion load by renal tubule secretion. The site of secretion is generally thought to be the proximal tubule. Although sulfate clearance ratios (C ratio-sulfate clearance/polyethylene glycol clearance) have been reported as high as 12 in SW-acclimated animals, the present study shows that net secretion ceases after acclimation to 10% SW (SO4 free). Intravenous infusion of sulfate into the latter induced net secretion within 5 h (C ratio increased from 0.83 +/- 0.23 to 2.12 +/- 0.33). Increased sulfate secretion coincided with an increase in the magnitude of HCO3-SO4 exchange in brush-border membrane vesicles (BBMV) isolated from flounder renal tubules. Treatment of 10% SW-acclimated flounder with 60 micrograms dexamethasone/100 g body wt also caused an increase in the HCO3-SO4 exchange in BBMV to a level comparable to that of BBMV from SW fish. The glucocorticoid effect was further tested in flounder renal tubule primary monolayer cultures. Measurement of unidirectional sulfate fluxes (J) showed that in the presence of cortisol net secretion (serosal-to-mucosal flux) dominated (Js----m = 111 +/- 6.5, Jm----s = 9 +/- 4.3, Jnet = 102 +/- 2.2 nmol.h-1.cm-2). Removal of cortisol from the culture medium significantly reduced net sulfate secretion to one-third of control (Js----m = 39 +/- 13.9, Jm----s = 6 +/- 1.0, Jnet = 33 +/- 14.1 nmol.h-1.cm-2).

Reversed polarity of Na(+) -K(+) -ATPase: mislocation to apical plasma membranes in polycystic kidney disease epithelia

1991 ◽  
Vol 260 (3) ◽  
pp. F420-F430 ◽  
Author(s):  
P. D. Wilson ◽  
A. C. Sherwood ◽  
K. Palla ◽  
J. Du ◽  
R. Watson ◽  
...  
Keyword(s):  
Kidney Disease ◽  
Polycystic Kidney Disease ◽  
Plasma Membranes ◽  
Renal Tubule ◽  
Apical Membrane ◽  
Membrane Vesicles ◽  
Renal Tubules ◽  
Polycystic Kidney ◽  
Permeable Membrane ◽  
Reversed Polarity

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder in which renal tubules become enormously enlarged due to fluid accumulation. Na(+) -K(+) -ATPase was compared in normal and cystic regions of whole kidneys and in confluent primary cultures of microdissected renal tubule and cyst-lining epithelia. Immunostaining with antibodies directed against the Na(+) -K(+) -ATPase catalytic alpha-subunit was confined to apical, luminal plasma membranes of ADPKD epithelia, which was a complete reversal of the normal renal tubule polarized location in basolateral membranes. Mislocated Na(+) -K(+) -ATPase was shown to be functionally active, because identical intense apical staining was observed by use of a cytochemical assay. In addition, biochemical assays showed a significant increase in these ouabain-inhibitable Na(+) -K(+) -ATPase specific activity levels in ADPKD kidneys compared with age-matched normal kidneys. Specific binding of [3H] ouabain was not only increased but also confined to the apical membrane vesicles prepared from cystic regions of ADPKD kidneys compared with normal age-matched controls, in which binding was confined to basolateral membrane vesicles. Although steady-state levels of Na(+) -K(+) -ATPase alpha- and beta-subunit in mRNAs were increased somewhat in ADPKD kidneys, this alone was not sufficient to account for the observed activation. Confluent ADPKD epithelia grown on dual-chamber, permeable membrane supports also showed reversed polarity of 22NaCl vectorial transport, because this was from basal to apical media compartments. Because this transport could also be blocked by ouabain, this suggested apical Na(+) -K(+) -ATPase was responsible and implicated altered polarity of Na(+) -K(+) -ATPase and resultant Na+ secretion as a mechanism for cyst formation in ADPKD. Because no reversal of polarity of other basolateral or apical membrane proteins was detected, an intracellular sorting defect specific for Na(+) -K(+) -ATPase is proposed.

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