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PubMed2000

In vivo measurements of relaxivities in the rat kidney cortex.

The aim of this study was to implement a novel noninvasive method to derive the in vivo T1 relaxivity (R1) and T2 relaxivity (R2) in the rat kidney cortex. A two-compartment gadolinium diethylene triamine pentaacetic acid (Gd-DTPA) distribution model was established to estimate the bolus and infusion dosages of Gd-DTPA necessary for obtaining the required steady-state concentration levels. After a single bolus injection of (99m)Tc-DTPA, several blood samples were collected. Based on considerations from the applied two-compartment model, a steady-state concentration was predicted approximately 5-10 minutes after the bolus injection. The plasma concentration levels of Gd-DTPA were measured by simultaneous injection of (99m)Tc-DTPA. Three regions in the cortex (upper, central, and lower) of both rat kidneys were used. A statistical evaluation resulted in the following in vivo relaxivities found at 7 T: R1 = 1.04 +/- 0.08 mM(-1)s(-1) and R2 = 10.78 +/- 0.83 mM(-1)s(-1). Using a 95% confidence interval, no intracortical differences were detected. The relaxivities R1 and R2 calculated in the intact rat kidney cortex were distinctly different from relaxivities found in human plasma: (22 degrees C) 4.42 +/- 0.07 mM(-1)s(-1) (r2> 0.98) and R2 = 5.75 +/- 0.17 mM(-1)s(-1) (r2> 0.98), respectively. The measurements showed a marked difference between in vitro and in vivo relaxivities. Comparison of the distribution rates in pig, human, and rats shows a distinct proportionality between size and renal function.

Animals↗
PubMed1967

Transport of monosaccharides in kidney-cortex cells.

1. The aerobic accumulation of various monosaccharides in slices of rabbit kidney cortex at 25 degrees was studied. 2. d-Fructose and alpha-methyl d-glucoside were readily accumulated against their concentration gradient by a phlorrhizin-sensitive Na(+)-dependent active transport. In the absence of external Na(+) the maximal rate of alpha-methyl glucoside transport was decreased tenfold, the K(m) of entry into the cells (8.2mm) not being affected. Phlorrhizin and d-galactose inhibited the entry of alpha-methyl glucoside also in the absence of external Na(+). 3. d-Xylose, 6-deoxy-d-glucose and 6-deoxy-d-galactose were poorly accumulated ([S](i)/[S](o) ratios slightly above 1.0); this transport was inhibited by phlorrhizin and by the absence of Na(+). 4. 3-O-Methyl-d-glucose, d-arabinose and l-arabinose were not actively transported, [S](i)/[S](o) ratios never exceeding 1.0. 5. 2-Deoxy-d-glucose and 2-deoxy-d-galactose were readily accumulated against a high concentration gradient, this transport being Na(+)-independent and only slightly sensitive to phlorrhizin. External Na(+) was not required for an inhibitory action of phlorrhizin and d-galactose on the entry of 2-deoxy-d-galactose into the cells. 6. Interference for entry into the cells between the following saccharides was found: d-galactose inhibited alpha-methyl d-glucoside transport; d-xylose entry was inhibited by d-glucose; d-galactose transport was inhibited by d-xylose; a mutual interference between d-galactose and its 2-deoxy analogue was found. 7. It is concluded that d-glucose, d-galactose, alpha-methyl d-glucoside, d-xylose and possibly also some other monosaccharides share a common active transport system. 8. The specificity of the Na(+)-dependent phlorrhizin-sensitive active transport system for monosaccharides in kidney-cortex cells differs from that in intestinal epithelial cells.

Animals↗
PubMed2000

Stimulatory effect of regucalcin on proteolytic activity is impaired in the kidney cortex cytosol of rats with saline ingestion.

The effect of regucalcin (RC) on neutral proteolytic activity in the cytosol of rat kidney cortex was investigated. Proteolytic activity was significantly increased by the presence of RC (0.01-0.10 microM) in the enzyme reaction mixture. This increase was completely abolished by the addition of anti-RC monoclonal antibody (150 ng/ml). When the renal cortex cytosol was incubated without RC addition, the degradation of globin of substrate was demonstrated by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. This degradation was clearly inhibited by the addition of anti-RC antibody (150 ng/ml), indicating that protein degradation results partly from the cytosolic endogenous RC. Meanwhile, proteolytic activity was significantly decreased in the renal cortex cytosol of rats with saline ingestion for 2, 7, and 14 days. The effect of RC (0.1 microM) in increasing proteolytic activity was weakened in the kidney cortex cytosol of saline-ingested rats. The present study suggests that endogenous RC plays a role in the activation of proteases in the renal cortex cytosol, and that the RC effect is impaired in saline-ingested rats.

Animals↗
PubMed1994

Effect of polyamines on glutamate dehydrogenase within permeabilized kidney-cortex mitochondria and isolated renal tubules of rabbit.

The effect of polyamines on glutamate dehydrogenase [L-glutamate: NAD(P) oxidoreductase (deaminating) [EC 1.4.1.3]) activity has been studied in both permeabilized kidney-cortex mitochondria and isolated renal tubules of rabbit. Spermidine was the most potent inhibitor of glutamate synthesis in permeabilized mitochondria resulting in about 80% decrease of the enzyme activity at 5 mM concentration. Putrescine, alpha-monofluoromethylputrescine (MFMP) and (R,R)-delta-methyl-alpha-acetylenic-putrescine (MAP) were more efficient than spermine. The inhibitory action of polyamines was potentiated by an elevated NADH content in the reaction mixture. Increasing concentrations of either NH4Cl, KCl or NaCl in the incubation medium resulted in a decrease of polyamine-induced inhibition of the enzyme activity, indicating that monovalent cations can compete with polyamines for the binding site at glutamate dehydrogenase. The inhibitory action of spermidine on glutamate synthesis was abolished by 2 mM ADP or 10 mM L-leucine, allosteric activators of the enzyme, as well as on the addition of either oxalate or sulphate at 20 mM concentrations. Spermidine did not affect glutamate formation when NADH was substituted by NADPH, suggesting an importance of the NADH binding to the inhibitory site of the enzyme for a decrease of reductive amination of 2-oxoglutarate by polyamine. Although spermidine did not influence glutamate deamination in the presence of NAD+, it stimulated this process by about 70% when NAD+ was substituted by NADP+. In the presence of ADP the stimulatory effect of polyamine was not significant. The data indicate that in permeabilized rabbit kidney-cortex mitochondria the effect of polyamines on both glutamate formation and glutamate deamination via the reaction catalysed by glutamate dehydrogenase is dependent upon the coenzyme utilized by the enzyme. In the presence of NADH their inhibitory effect on the glutamate formation may be alleviated by allosteric activators of the enzyme, and concentrations of potassium, sodium, sulphate and oxalate. In isolated rabbit renal tubules incubated with 5 mM methionine sulfoximine and aminooxyacetate, in order to inhibit glutamine synthetase and aminotransferases, respectively, 5 mM spermidine decreased glutamate formation by about 30%, while putrescine and spermine did not significantly diminish the enzyme activity. In the presence of octanoate glutamate formation was reduced by about 30% by naturally occurring polyamines as well as MFMP and MAP, indicating that under these conditions NADH rather than NADPH is utilized as the coenzyme. In view of these data it is possible to suggest that polyamines may be of importance to control glutamate dehydrogenase activity under physiological conditions.

Animals↗
PubMed1981

Bronchial mucosal and kidney cortex affinity of 4- and 4,4'-substituted sulphur-containing derivatives of 2,2'-5,5'-tetrachlorobiphenyl in mice.

In order to evaluate further the structural requirements previously proposed for accumulation of polychlorinated biphenyls (PCB) and their sulphur-containing metabolites in the respiratory tract of mice, 4-methylthio-, 4-methylsulphonyl and 4,4'-bis(methylthio)-2,2',5,5'-[14C] tetrachlorobiphenyl were studied by whole body autoradiography. All the compounds gave rise to a strong accumulation of radioactivity in the mucosa of the bronchi, trachea and larynx. The first two substances were also concentrated in the mucosa of the nasal cavities. At the longer post-injection times all the compounds studied were localized in distinct sites of the kidney cortex. However, while the uptake of the monosubstituted sulphur-containing tetrachlorobiphenyl metabolites there was comparatively weak, the bis(methylthio) derivative showed a remarkable accumulation and retention in the kidney cortex. The study makes it possible to formulate the structural requirements for bronchial accumulation on the basis of the structure of the compounds that are accumulated rather than on the structure of the unmetabolized polychlorobiphenyls. Also with regard to the uptake in the kidney cortex a specific structure-dependency seems to exist.

Animals↗
PubMed1992

Glutamine affects glutamate metabolism in isolated rat kidney cortex mitochondria.

The active state respiration of isolated rat kidney cortex mitochondria with 10 mM glutamate as single substrate is substantially increased by the addition of 10 mM glutamine. This increase in respiration was accompanied by a higher transamination rate and was found to be insensitive to the selective inhibition of either the transamination or the desamination pathway of glutamate oxidation. These data can be explained by an approximately 2-fold elevated intramitochondrial glutamate concentration observed in the additional presence of glutamine.

Aminooxyacetic Acid↗
PubMed1994

Alpha 2-adrenergic receptors of the alpha 2c subtype mediate inhibition of norepinephrine release in human kidney cortex.

The pharmacological properties of the alpha 2-adrenergic receptors regulating the release of norepinephrine were investigated in human kidney cortex. Slices were preincubated with [3H]norepinephrine, superfused in the presence of desipramine, and stimulated electrically. Two procedures were used to estimate the affinity of alpha-adrenergic antagonists at the autoreceptors. First, pEC30 values (negative logarithms of antagonist concentrations that increased the electrically evoked overflow of tritium by 30%) were determined. Second, antagonist pKd values were determined against the overflow-inhibiting effect of the alpha 2 receptor-selective agonist UK 14,304. Antagonist pEC30 values correlated well with the respective pKd values (r = 0.96, p < 0.01). The site of action of the phenylethylamine norepinephrine, as well as of the imidazoline derivative UK 14,304, is an alpha 2-adrenergic receptor. Neither the cyclooxygenase inhibitor indomethacin nor the adenosine receptor antagonist 8-sulfophenyltheophylline changed the concentration-inhibition curve of UK 14,304. When compared with binding data from the literature, the pEC30 values correlated best with the antagonist affinities at alpha 2c binding sites in an opossum kidney cell line and rat brain cortex (r > or = 0.95, p < 0.001) and at the affinities of alpha 2c sites obtained in COS cells transfected with either the human alpha 2-C4 or rat RG10-alpha 2 gene (r > or = 0.95, p < 0.01). In contrast, the correlations with alpha 2A, alpha 2B, and alpha 2D sites were not as good. Moreover, the alpha 2-autoreceptors in human kidney cortex were very similar to the alpha 2C-adrenergic receptors mediating prostaglandin synthesis in rabbit aorta but differed from alpha 2A- and alpha 2D-autoreceptors in rabbit and rat tissues. It is concluded that in human kidney cortex prejunctional autoreceptors are alpha 2C.

Adrenergic alpha-Agonists↗
PubMed1977

Purification and some properties of arylsulphatases A and B from rabbit kidney cortex.

Arylsulphatases A and B (EC 3.1.6.1) of rabbit kidney cortex were purified 5250- and 7720-fold respectively by a multiple-column-chromatography method. The specific activity toward 4-nitrocatechol sulphate was 42mumol/min per mg for arylsulphatase A and 62 mumol/min per mg for arylsulphatase B. Each enzyme migrated as a single band on polyacrylamide-gel electrophoresis, and the enzyme activity corresponded to the band of protein on the gel. The rate of hydrolysis of ascorbic acid 2-sulphate by arylsulphatase A was three times that for cerebroside 3-sulphate. Arylsulphatase B hydrolysed UDP-N--acetylgalactosamine 4-sulphate and glucosamine 4,6-disulphate, but not galactosamine 6-sulphate.

Animals↗
PubMed1984

Inhibition of 2-oxoglutarate metabolism by lithium in the isolated rat kidney cortex tubules.

2-Oxoglutarate metabolism in the isolated rat kidney cortex tubules was inhibited by lithium at 5 mM concentration, and at pH increased from 7.1 to 7.6. The metabolism of pyruvate and acetylcarnitine to citrate and 2-oxoglutarate was enhanced by lithium and the increased pH value. The content of 2-oxoglutarate in the renal tubular cells was lowered by lithium but increased at elevated pH values. Both the intracellular pH value and bicarbonate ion concentrations in renal tubular cells were increased by lithium in the medium containing 2-oxoglutarate. The results obtained indicate that lithium disturbs renal metabolism by intracellular alkalization, with a simultaneous inhibition of the inflow of dicarboxylic substrates to the renal tubular cells.

Animals↗
PubMed1980

Some properties of pig kidney-cortex aldehyde reductase.

Aldehyde reductase was purified from pig kidney cortex to homogeneity by a new procedure. The molecular weight of the enzyme was estimated by sedimentation equilibrium to be 43 700 and by gel electrophoresis in the presence of sodium dodecyl sulphate to be 41 700. The enzyme is clearly a monomer. The enzyme preparation contained no significant quantities of zinc, manganese or copper and had no essential histidine or thiol groups. Changes in the absorption and fluorescence spectra of NADPH were observed on formation of the enzyme-NADPH complexes. Large changes in the fluorescence spectra were also observed in the presence of sodium barbitone or Warfarin. These changes were used as the basis of active-site titrations, which showed that the enzyme had one active site per molecule. The dissociation constants of NADPH and NADP+ from binary complexes with the enzyme were estimated in spectrophotometric titrations.

Alcohol Oxidoreductases↗
PubMed1987

[Effect of a NaCl gradient on the transport of para-aminohippuric acid into the vesicles of the basolateral membrane of the kidney cortex].

Basolateral membrane vesicles were isolated from the rat kidney cortex by a modified method of cation precipitation. Different steps of preparation were analysed using the marker enzymes: Na+,K+-ATPase (for basolateral membrane), alkaline phosphatase (for apical membrane), glucose-6-phosphatase (for membranes of endoplasmic reticulum) and succinate dehydrogenase (for mitochondria). The basolateral membrane was purified by a 8-9-fold treatment with Na+,K+-ATPase, while other membrane contaminations were as low as 2% (as compared to homogenate). The transport of 3H-p-aminohippurate (3H-PAH) by basolateral membrane vesicles was measured under different experimental conditions. The 3H-PAH uptake was found to be Na-gradient dependent. The initial rate of 3H-PAH uptake in the presence of NaCl gradient (500 pM/mg X min) was higher than without the gradient (88 pM/mg X min). It is concluded that the PAH transfer across the basolateral membrane may be energized by the Na+ chemical gradient.

Aminohippuric Acids↗
PubMed1992

Purification and characterization of glucosamine-6-phosphate deaminase from dog kidney cortex.

Glucosamine-6-phosphate deaminase (EC 5.3.1.10) from dog kidney cortex was purified to homogeneity, as judged by several criteria of purity. The purification procedure was based on two biospecific affinity chromatography steps, one of them using N-epsilon-amino-n-hexanoyl-D-glucosamine-6-phosphate agarose, an immobilized analog of the allosteric ligand, and the other by binding the enzyme to phosphocellulose followed by substrate elution, which behaved as an active-site affinity chromatography. The enzyme is an hexameric protein of about 180 kDa composed of subunits of 30.4 kDa; its isoelectric point was 5.7. The sedimentation coefficient was 8.3S, and its frictional ratio was 1.28, indicating that dog deaminase is a globular protein. The enzyme displays positive homotropic cooperativity toward D-glucosamine-6-phosphate (Hill coefficient = 2.1, pH 8.8). Cooperativity was completely abolished by saturating concentrations of GlcNAc6P; this allosteric modulator activated the reaction with a typical K-effect. Under hyperbolic kinetics, a Km value of 0.25 +/- 0.02 mM for D-glucosamine-6-phosphate was obtained. Assuming six catalytic sites per molecule, kcat is 42 s-1. Substrate-velocity data were fitted to the Monod's allosteric model for the exclusive-binding case for both substrate and activator, with two interacting substrate sites. The Kdis for N-acetyl-D-glucosamine-6-phosphate was estimated at 14 microM.

Aldose-Ketose Isomerases↗
PubMed1992

Expression of Na(+)-independent amino acid transport in Xenopus laevis oocytes by injection of rabbit kidney cortex mRNA.

Poly(A)+ mRNA was isolated from rabbit kidney cortex and injected into Xenopus laevis oocytes. Injection of mRNA resulted in a time- and dose-dependent increase in Na(+)-independent uptake of L-[3H]alanine and L-[3H]arginine. L-Alanine uptake was stimulated about 3-fold and L-arginine uptake was stimulated about 8-fold after injection of mRNA (25-50 ng, after 3-6 days) as compared with water-injected oocytes. T.I.C. of oocyte extracts suggested that the increased uptake actually represented an increase in the oocyte content of labelled L-alanine and L-arginine. The expressed L-alanine uptake, obtained by subtracting the uptake in water-injected oocytes from that in mRNA-injected oocytes, showed saturability and was inhibited completely by 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH) and L-arginine. The expressed L-arginine uptake in mRNA-injected oocytes also showed saturability, being completely inhibited by L-dibasic amino acids) and partially inhibited by BCH. Expression of both L-alanine and L-arginine uptake showed clear cis-inhibition by cationic (e.g. L-arginine) and neutral (e.g. L-leucine) amino acids. In all, this points to the expression of a Na(+)-independent transport system with broad specificity (i.e. b degree, (+)-like). In addition, part of the expressed uptake of L-arginine could be due to a system y(+)-like transporter. After size fractionation through a sucrose density gradient, the mRNA species encoding these increased transport activities (Na(+)-independent transport of L-alanine and of L-arginine) were found in fractions of an average mRNA chain-length of 1.8-2.4 kb. On the basis of these results, we conclude that Na(+)-independent transport system(s) for L-alanine and L-arginine from rabbit renal cortical tissues, most likely proximal tubules, are expressed in Xenopus laevis oocytes. These observations may represent the first steps towards expression and cloning of these transport pathways.

Alanine↗
PubMed1986

Localization and role of pyruvate kinase isoenzymes in the regulation of carbohydrate metabolism and pyruvate recycling in rat kidney cortex.

This work was performed to gain more information on the role of pyruvate kinase isoenzymes in the regulation of renal carbohydrate metabolism. Immunohistochemically, pyruvate kinase type L is shown to be localized in the proximal tubule of the nephron and pyruvate kinase type M2 in the distal tubule and the collecting duct. a tight relationship between gluconeogenesis and pyruvate recycling was found. The rate of gluconeogenesis (8 mumol/g wet wt. per 30 min) was of the same order of magnitude as the rate of pyruvate recycling (10.92 mumol/g wet wt. per 30 min). Stimulation of gluconeogenesis from 20 mM lactate in kidney cortex slices of 24-h-starved rats by dibutyryl-cAMP, alanine and parathyroid hormone was connected with a decrease in pyruvate recycling; inhibition of gluconeogenesis due to a lack of Ca2+ in the incubation medium was linked with an increase in pyruvate recycling. The degradation of [6-14C]glucose to lactate, pyruvate, ketone bodies and CO2 and of [2-14C]lactate was unaffected by dibutyryl-cAMP, alanine, epinephrine, vasopressin or the omission of Ca2+ from the incubation medium. 1 mM dibutyryl-cAMP or 5 mM alanine did not alter the activities of oxaloacetate decarboxylase, 'malic' enzyme and malate dehydrogenase from rat kidney cortex. Since aerobic glycolysis in the distal tubules and the collecting ducts is not influenced by hormones, dibutyryl-cAMP and Ca2+, pyruvate kinase type M2 residing in this tissue is unlikely to be a control point of glycolysis. Since this tissue degrades only one-seventh of the glucose formed via gluconeogenesis, it does not contribute significantly to pyruvate recycling. Therefore, the decrease of pyruvate recycling in the presence of dibutyryl-cAMP and alanine in rat kidney cortex slices, leading to increased renal gluconeogenesis, has to be ascribed to the regulation of pyruvate kinase type L.

Alanine↗
PubMed1987

Biochemical effects of gentamicin on rat kidney cortex. I. Analytical subfractionation of control tissue.

As a first step in studies of the molecular mechanism(s) underlying gentamicin toxicity, rat kidney cortex has been subfractionated using differential centrifugation. An analytical, rather than preparative approach was used. DNA was used as a marker for the nuclei, cytochrome oxidase for mitochondria, acid phosphatase for lysosomes, catalase for peroxisomes, NADPH-cytochrome c reductase for the endoplasmic reticulum, p-nitrophenyl-alpha-mannosidase (at pH 5.5) for the Golgi apparatus, AMPase for the plasma membrane in general, and alkaline phosphatase for the brush border, and lactate dehydrogenase for the cytosol. In addition, electron microscopy was performed on the subfractions obtained. The distributions of subcellular markers obtained here for the rat kidney cortex closely resemble the corresponding distributions reported for rat liver. This procedure can now be used to look for biochemical and/or toxic changes which might be reflected in an altered distribution pattern for marker enzymes.

Acetylglucosaminidase↗
PubMed1976

Effect of glucose utilization inhibitor isolated from the serum and urine of patients with chronic renal failure on the free fatty acid metabolism in rat kidney cortex slices.

The authors studied interference by the inhibitor of glucose utilization with free fatty acid (FFA) metabolism in rat kidney cortex slices. They found that FFA uptake by the kidneys, their incorporation into triglycerides (TG) and oxidation to 14CO2 were lower when the inhibitor was present in the incubation medium. The findings show that the inhibitor, as well as inhibiting glucose utilization in various tissues, interferes directly with fat metabolism.

Animals↗
PubMed1994

Asymmetrical distribution of L-isoaspartyl protein carboxyl methyltransferases in the plasma membranes of rat kidney cortex.

We have studied the distribution of membrane-associated L-isoaspartyl protein carboxyl methyltransferases (PCMTs) in plasma membranes purified from rat kidney cortex. Addition of CHAPS to brush-border membranes (BBM) and basolateral membranes (BLM) was required to measure optimal membrane-dependent methylation of ovalbumin and TS-isoD-YSKY, substrates of L-isoaspartyl PCMTs. Extraction of both membrane-associated enzymes was achieved with detergents, but not with high-salt solutions, suggesting a strong membrane attachment. However, upon phase partitioning using Triton X-114, both enzymes were predominantly associated with the detergent-poor phase, suggesting a relatively hydrophilic nature. The enzymes showed similar catalytic properties such as substrate recognition and affinity towards the methyl donor, S-adenosyl-L-methionine. The activity of the BBM enzyme, however, was about 2-fold higher than that of the BLM enzyme. Identification of the endogenous substrates located in the two plasma membranes by acidic gel electrophoresis in the presence of a cationic detergent revealed significant differences in the methyl-accepting proteins of both membranes. The BBM-methylated proteins had sizes of 35, 50 and 54 kDa, whereas the major BLM-methylated substrates were of 97 and 100 kDa. The enzymes showed distinct behaviour on Mono Q anion-exchange chromatography. The BBM-associated PCMT did not bind to the column, being eluted in the flow-through, whereas the BLM enzyme bound to the column and was eluted at 0.15 M NaCl. Moreover, the two enzymes had different molecular masses under both denaturing and nondenaturing conditions, the BLM PCMT migrating at an apparent molecular mass of 29 kDa, compared with 27 kDa for the BBM enzyme. Taken together, these results show the presence of two distinct L-isoaspartyl PCMTs in the plasma membranes of the kidney cortex.

Animals↗
PubMed1982

Activities of some enzymes of glucose metabolism in bovine liver and kidney cortex at three stages of lactation.

The activities (per g of tissue) of hexokinase, phosphofructokinase and pyruvate kinase were unchanged throughout lactation in liver and in kidney cortex. In both these tissues glucose 6-phosphatase activity decreased during late lactation. At the same time fructose diphosphatase activity increased in kidney cortex but not in liver. Activities of the pentose cycle dehydrogenases and of aspartate aminotransferase tended to increase in mid lactation. For most enzymes the activities at peak lactation were similar to those for dry, non-pregnant cows and there was no specific response of the gluconeogenic enzymes. Total hepatic contents of most enzymes tended to increase in mid lactation, but the changes were not clear cut and were the result of an increase in liver size.

Animals↗