Characteristics of renal transport of taurine in reptilian brush-border membranes

We examined characteristics of taurine transport across renal brush-border membranes (BBM) of the garter snake (Thamnophis sirtalis), a species that demonstrates both net reabsorption and secretion of taurine in vivo. Transport was examined by a rapid filtration technique at 25 degrees C. Inwardly directed Na+ gradient specifically stimulated taurine uptake. Under initial taurine equilibrium condition, a small overshoot of taurine uptake driven by an inwardly directed NaCl gradient could be observed. No stimulation of taurine uptake was observed under Na+ equilibrium or K+, Li+, or choline gradients conditions. Reptilian renal BBM taurine transport also displayed specific Cl- requirement: replacement of NaCl by NaSCN or Na(+)-gluconate gradients inhibited taurine uptake. The uptake was stimulated under Cl- gradient compared with Cl- equilibrium conditions. Taurine transport was not stimulated by H+ gradient in either direction, although it was inhibited by acidic pH (less than 7.0). Amiloride and furosemide had no effects. The transport was electrogenic, stimulated by an inside negative membrane potential, and inhibited by other beta-amino acids. Overall, the reptilian BBM transport system for taurine resembles those observed in both mammalian and fish renal BBM.

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NAD-glycohydrolase in renal brush border membranes

AJP Renal Physiology ◽

10.1152/ajprenal.1985.249.3.f366 ◽

1985 ◽

Vol 249 (3) ◽

pp. F366-F373

Author(s):

S. A. Kempson

Keyword(s):

Brush Border ◽

Osmotic Shock ◽

Phosphate Transport ◽

Reaction Products ◽

Brush Border Membranes ◽

Nad Glycohydrolase ◽

Renal Brush Border Membranes ◽

Renal Brush Border

NAD is hydrolyzed during incubation with isolated renal brush border membranes (BBM). The specific enzymatic mechanisms have not been identified apart from the activity of ADP-ribosyltransferase, which accounts for a very small proportion of the total hydrolysis. In the present study, an NAD-glycohydrolase (NGH) was identified in the renal BBM using the cyanide-addition assay to monitor hydrolysis of NAD at the nicotinamide-ribose bond. The production of nicotinamide and ADP-ribose, the expected reaction products, was determined by thin-layer chromatography. The NGH was enriched ninefold in the BBM fraction and accounted for 36% of the total rate of NAD hydrolysis by BBM enzymes at pH 7.4. Assay of NGH in sealed BBM vesicles subjected to osmotic shock indicated that about 23% of the NGH is exposed on the cytoplasmic surface of the BBM. The enzyme was inhibited by nicotinamide in vitro and also when the nicotinamide was administered in vivo, suggesting, indirectly, that the enzyme may play a role in mediating the effects of nicotinamide on BBM phosphate transport.

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Renal uptake of myoglobin is mediated by the endocytic receptors megalin and cubilin

AJP Renal Physiology ◽

10.1152/ajprenal.00062.2003 ◽

2003 ◽

Vol 285 (3) ◽

pp. F451-F458 ◽

Cited By ~ 42

Author(s):

Jakub Gburek ◽

Henrik Birn ◽

Pierre J. Verroust ◽

Boguslawa Goj ◽

Christian Jacobsen ◽

...

Keyword(s):

Renal Failure ◽

Acute Renal Failure ◽

Molecular Mechanism ◽

Brush Border ◽

Surface Plasmon Resonance Analysis ◽

Receptor Associated Protein ◽

Brush Border Membranes ◽

Renal Brush Border Membranes ◽

Renal Brush Border

Nephrotoxicity of myoglobin is well recognized as playing a part in the development of acute renal failure in settings of myoglobinuria. However, the molecular mechanism of myoglobin uptake in renal proximal tubules has not been clarified. Here, we report that the endocytic receptors megalin and cubilin are involved in renal reabsorption of myoglobin. Both receptors were captured from solubilized renal brush-border membranes by affinity chromatography using myoglobin-Sepharose. Myoglobin bound to purified megalin and cubilin with Kdvalues of 2.0 and 3 μM, respectively, as evaluated by surface plasmon resonance analysis. Apomyoglobin bound to megalin with the same affinity, and the affinity of apomyoglobin to cubilin was reduced ( Kd= 5 μM). Radioiodinated myoglobin could be displaced by apomyoglobin in inhibition studies using isolated renal brush-border membranes ( Ki∼ 2 μM). Receptor-associated protein as well as antibodies directed against megalin and cubilin markedly inhibited the uptake of fluorescent-labeled myoglobin by cultured yolk sac BN-16 cells. The significance of megalin- and cubilin-mediated endocytosis for myoglobin uptake in vivo was demonstrated by use of kidney-specific megalin knockout mice. Injected myoglobin was extensively reabsorbed by megalin-expressing proximal tubular cells, whereas there was very little uptake in the megalin-deficient cells. In conclusion, this study establishes the molecular mechanism of myoglobin uptake in the renal proximal tubule involving the endocytic receptors megalin and cubilin. Identification of the receptors for tubular uptake of myoglobin may be essential for development of new therapeutic strategies for myoglobinuric acute renal failure.

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Enzymatic and transport characteristics of isolated snake renal brush-border membranes

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1988.255.1.r52 ◽

1988 ◽

Vol 255 (1) ◽

pp. R52-R60 ◽

Cited By ~ 3

Author(s):

S. Benyajati ◽

W. H. Dantzler

Keyword(s):

Brush Border ◽

Transport Systems ◽

Disulfonic Acid ◽

Thamnophis Sirtalis ◽

Organic Solutes ◽

Gamma Glutamyl Transpeptidase ◽

Brush Border Membranes ◽

Brush Border Enzyme ◽

Glutamyl Transpeptidase ◽

Filtration Technique

Brush-border membranes (BBM) of proximal tubules were isolated from the kidney of the garter snake (Thamnophis sirtalis) by a procedure involving hypotonic lysis, Ca precipitation, and differential centrifugation. The isolated membranes were enriched 15-fold in brush-border enzyme activities (alkaline phosphatase, gamma-glutamyl transpeptidase) compared with whole kidney homogenates and were substantially free of other contaminating membranes. The yield of the BBM preparation was 40%. The BBM vesicular transport of several organic solutes was characterized by a rapid filtration technique at 25 degrees C. D-glucose, p-aminohippurate (PAH), and urate entered the same osmotically active space (2-3 microliter/mg protein) and binding was minimal (less than 20% for PAH). An uptake overshoot for 3-O-methyl-D-glucose (20 microM) by reptilian BBM was observed only in the presence of an inwardly directed NaCl gradient and was abolished by 0.1 mM phlorizin. Reptilian BBM exhibited Na-gradient-stimulated uptake of PAH (90 microM) with an overshoot that was inhibited by other organic acids and by 4-acetamido-4'-isothiocyanostilbene-2, 2'-disulfonic acid (SITS). In contrast, urate uptake (30 microM) appeared to be Na independent and not appreciably affected by other organic anions or SITS. The presence of specific transport systems for organic solutes in the isolated membrane preparation distinctly characterizes the BBM of reptilian kidney.

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Basolateral taurine transport system in reptilian renal cells

AJP Renal Physiology ◽

10.1152/ajprenal.1994.266.3.f439 ◽

1994 ◽

Vol 266 (3) ◽

pp. F439-F449 ◽

Cited By ~ 1

Author(s):

S. Benyajati ◽

S. M. Bay

Keyword(s):

Brush Border ◽

Choline Chloride ◽

Basolateral Membrane ◽

Membrane Vesicles ◽

Garter Snake ◽

Marker Enzyme ◽

Renal Cells ◽

Taurine Transport ◽

Taurine Uptake

The characteristics of taurine transport across renal basolateral membranes were examined, using basolateral membrane vesicles (BLMV) isolated from garter snake (Thamnophis spp.) kidneys. BLMV fraction exhibited high enrichment for the basolateral marker enzyme, Na(+)-K(+)-adenosinetriphosphatase (23-fold), with approximately 10% contamination by brush-border membranes. Taurine uptake into BLMV was specifically stimulated by inwardly directed Na+ gradient in the presence of Cl-. Equilibrium NaCl condition and replacement of NaCl gradient by KCl, choline chloride, NaSCN, sodium gluconate, or mannitol inhibited taurine uptake. Unlike brush-border membrane vesicles (BBMV), taurine uptake into BLMV was not stimulated by a Cl- gradient. In further contrast to BBMV, BLMV taurine uptake was smaller in magnitude and not electrogenic. The stoichiometric relationship between Na+ and BLMV taurine uptake, determined by activation method, indicated a 1 Na+:1 taurine interaction, in contrast to the 3 Na+:1 taurine stoichiometry for BBMV taurine transport. Bromcresol green inhibited BBMV taurine transport but had no effect on BLMV taurine uptake. Efflux of taurine from BLMV was faster than that from BBMV. Unlike BBMV, the BLMV efflux was stimulated by external taurine. The observed characteristics of taurine transport on both membranes would integratively result in net transepithelial reabsorption of taurine across renal cells of the garter snake, a species that demonstrates both net reabsorption and secretion of taurine in vivo.

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