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PubMed1988

Changes in lysosome populations in the rat kidney cortex induced by experimental proteinuria.

1. Experimental proteinuria (262.9 mg protein/24 hr urine) was induced in rats by repeated intraperitoneal injections of BSA. 2. Hypertrophy of the kidney cortex was significant 8 days after the start of the BSA injections, and the activities of lysosomal enzymes in kidney cortex and urine were significantly higher in proteinuric compared to nonproteinuric rats. 3. Lysosome populations in the kidney cortex were examined by rate sedimentation of the homogenate and by rate zonal and isopycnic centrifugation of the lysosome-rich ML fraction. 4. The activity of lysosomal enzymes in the kidney cortex increased slightly, essentially in the large, fragile lysosomes mainly recovered from the proximal tubule. 5. Proteinuria induced a shift/reduction in the density of small lysosomes from 1.235 and 1.20 g/ml to 1.225 and 1.185 g/ml, respectively. 6. Proteinuria induced a new population of small lysosomes (density 1.185 g/ml) enriched in cathepsin D.

Animals↗
PubMed2001

Effect of dexmedetomidine on the release of [3H]-noradrenaline from rat kidney cortex slices: characterization of alpha2-adrenoceptor.

The presynaptic modulation of [3H]-noradrenaline (NA) release from rat kidney cortex slices, a method used for the first time, was investigated. Rat kidney cortex slices were loaded with [3H]-NA and the release of radioactivity at rest and in response to field stimulation was determined. The alpha(2)-adrenoceptor agonist, dexmedetomidine inhibited the stimulation-evoked release of NA from kidney slices in a concentration-dependent manner, whereas alpha(2)-adrenoceptor antagonist CH-38083 (7,8-methyenedioxy-14-alpha-hydroxyalloberbane HCl), an alpha(2)-adrenoceptor antagonists, enhanced it. When dexmedetomidine and BRL-44408, a selective alpha(2A) antagonist, were added together, the effect of dexmedetomidine was significantly antagonized. In contrast, ARC-239 (2-(2,4-(o-piperazine-1-yl)-ethyl-4,4-dimethyl-1,3-(2H, 4H)disoguinolinedione chloride), a selective alpha(2B)-antagonist, had no effect on the release and failed to prevent the effect of dexmedetomidine. Prazosin, an alpha(1)- and alpha(2B/C)-adrenoceptor antagonist enhanced the release evoked by field stimulation. It is therefore suggested that there is a negative feedback modulation of NA release at the sympathetic innervation of kidney cortex, and dexmedetomidine, a clinically used anesthetic adjunct inhibits the release via activation of alpha(2C)-adrenoceptors.

Adrenergic alpha-2 Receptor Agonists↗
PubMed1984

Liver and kidney cortex gluconeogenesis from L-alanine in fed and starved rats.

Circulating [14C]glucose 2, 5 and 10 min after intravenous injection of [U-14C]-L-alanine was greater in 24 hr starved than in fed rats. In vitro uptake of [14C]alanine by liver and kidney cortex slices from 24 hr starved and fed rats rose in parallel with increased medium substrate concentration. Formation of [14C]glucose from 1mM [14C]alanine was similar in liver and kidney cortex slices and increased in tissues from 24 hr starved compared with fed rats. With 5 mM [14C]alanine more [14C]glucose was produced by liver than by kidney cortex slices from 24 hr starved rats. Liver slices always produced more [14C]lactate and less [14C]-CO2 from [14C]alanine than kidney cortex slices. It is proposed that under physiological conditions, the kidneys cortex actively participates in glucose production from alanine.

Alanine↗
PubMed1986

Renin granules isolated from rat kidney cortex by continuous colloidal silica (Percoll) density gradient centrifugation.

Renin granules were isolated from rat kidney cortex by a continuous polyvinyl-pyrrolidone-coated colloidal silica (Percoll) density gradient centrifugation. A major peak of renin activity was found at a density of 1.12-1.13 g/ml, and the specific activity of renin in the peak fraction was increased by approximately 70-fold, as compared with that in the kidney cortex homogenate. On the other hand, activities of other reference enzymes, such as succinate dehydrogenase, acid phosphatase and glucose-6-phosphatase, were not detectable in the peak fraction. When the extract of the peak fraction was applied to a pepstatin column, trypsin-activated renin could not be detected in the breakthrough fractions. These results indicate that renin granules of the rat kidney cortex contain only active renin.

Animals↗
PubMed1976

Renin substrate in granules from rat kidney cortex.

1. Subcellular fractions of rat kidney cortex generated angiotensin I continuously over 2h when incubated at 37degreesC with rat renin, indicating the presence of renin substrate within cells in the renal cortex. 2. Renin substrate was located in highest specific concentration in particulate fractions. The particles containing renin substrate had a sedimentation velocity slightly lower than mitochondria and renin granules but greater than the microsomal fraction. 3. Isopycnic gradient centrifugation indicated a density of 1.190g/ml for the particles containing renin substrate, compared with 1.201 for renin granules, 1.177 for mitochondria, and 1.170 and 1.230 for lysosomes in the heavy-granule fraction. 4. In the liver, renin substrate was also found in particles, but these had a lower sedimentation rate than those from the kidney. 5. The molecular weights of renin substrate in kidney and liver granules and rat plasma were similar, namely 61000-62000. 6. On the basis of these biochemical findings, a mechanism for the intrarenal production of angiotensin, incorporating a subcellular reaction scheme, is proposed.

Angiotensin II↗
PubMed1983

Secretion control for active and inactive renin: effects of calcium and potassium on rabbit kidney cortex slices.

Release of active and inactive renin by rabbit kidney cortex slices was investigated. Inactive renin was estimated as the increase in renin activity after acidification (pH 2.8) of slice supernatant solutions. In Ca2+-free media, release of both active and inactive renin was increased but the changes in inactive renin were more marked. The percentage of total renin released which was inactive ranged from 8.3% ([Ca2+] = 9.2 mM) to 34.5% (zero [Ca2+]) with a linear relationship (r = -0.96) over the range of [Ca2+] studied. Depolarizing media ([K+] = 20 mM) suppressed release of inactive renin more than release of the active form. This effect, for both forms of renin, was lost when Ca2+ ions were omitted from the incubation media. This suggests that influx of Ca2+ ions was responsible for the reduced renin secretion following depolarization of the juxtaglomerular cells. Reducing the [K+] of the incubation buffer from 5.7 mM (control) to 1.0 mM did not alter active renin but increased release of inactive renin. Low [K+] media abolished the stimulatory effect of low [Ca2+] on release of both forms of renin. In incubation media with low [Ca2+] or with low [K+] the mixture of renins released by the kidney cortex slices correlated with that found in extracts of non-incubated kidney: that is, about 35% of the total renin was in the inactive form. Mechanisms controlling the secretion of active and inactive renins by the kidney are at least partially independent. Differential secretion of the two forms, perhaps linked to regulation of the activation of inactive renin before release, appears to be the basis of a control step in the over-all expression of the renin-angiotensin system. This may be coupled in some way to juxtaglomerular cell Na+ ion flux.

Animals↗
PubMed2002

Role of endogenous regucalcin in transgenic rats: suppression of kidney cortex cytosolic protein phosphatase activity and enhancement of heart muscle microsomal Ca2+-ATPase activity.

Rats were generated by pronuclear injection of the transgene with a cDNA construct encoding rat regucalcin that is a regulatory protein of Ca2+ signaling. Transgenic (TG) founders were fertile, transmitted the transgene at the expected frequency, and bred to homozygote. Western analysis of the cytosol prepared from the tissue of TG female rats (5-week-old) showed a remarkable expression of regucalcin (3.3 kDa) protein in the liver, kidney cortex, heart, lung, stomach, brain, spleen, muscle, colon, and duodenum. Regucalcin expression of TG male rats was seen in the liver, kidney cortex, heart, and lung. In wild-type (wt) male and female rats, regucalcin was mainly present in the liver and kidney cortex. Regucalcin inhibited protein phosphatase activity in rat kidney cortex cytosol and activated Ca2+-ATPase activity in rat heart muscle microsomes. The suppressive effect of regucalcin on protein phosphatase activity was significantly enhanced in the cytosol of kidney cortex of TG male and female rats as compared with those of wt rats. Likewise, heart muscle microsomal Ca2+-ATPase activity was significantly enhanced in TG rats. The changes in their enzyme's activities in TG rats were completely abolished in the presence of anti-regucalcin monoclonal antibody (100 ng/ml) in the enzyme reaction mixture. Moreover, the body weight of TG female rats was significantly lowered as compared with that of wt rats. Serum inorganic phosphorus concentration was significantly increased in TG male and female rats, while serum calcium, glucose, triglyceride, free cholesterol, albumin, and urea nitrogen concentrations were not significantly altered in TG rats. Regucalcin TG rats should be a useful model to define a regulatory role of endogenous regucalcin in the tissues in vivo.

Animals↗
PubMed1978

Ionic and metabolic requirements for decamethonium transport in mouse kidney cortex slices.

Decamethonium accumulates in mouse kidney cortex slices incubated in Krebs-Ringer bicarbonate buffer (37 degrees C, pH 7.4) aerated with O2-CO2 95:5 v/v%. Maximum tissue-medium accumulation ratio decreased with increasing external decamethonium concentration. Decamethonium was released from the tissue at a slow rate. The metabolic inhibitor cyanide inhibited accumulation of decamethonium but did not produce release of decamethonium already accumulated in the tissue. Substitution of external Na+ by other cations depressed decamethonium uptake. However, this cannot be ascribed to absence of Na+ since no inhibition occurred when Na+ was substituted by isoosmotic sucrose. Decamethonium uptake is inhibited when active Na+-transport is impaired (omission of K+ or addition of ouabain). The slow onset of this inhibition is compatible with the idea that it may be secondary to changes in the intracellular electrolyte concentrations. Furthermore, decamethonium uptake was depressed in absence of external Ca2+.

Animals↗
PubMed1973

Binding of parathyroid hormone to bovine kidney-cortex plasma membranes.

1. Plasma membranes were purified from bovine kidney cortex, with a fourfold increase in specific activity of parathyroid hormone-sensitive adenylate cyclase over that in the crude homogenate. The membranes were characterized by enzyme studies. 2. Parathyroid hormone was labelled with (125)I by an enzymic method and the labelled hormone shown to bind to the plasma membranes and to be specifically displaced by unlabelled hormone. Parathyroid hormone labelled by the chloramine-t procedure showed no specific binding. (75)Se-labelled human parathyroid hormone, prepared in cell culture, also bound to the membranes. 3. Parathyroid hormone was shown to retain biological activity after iodination by the enzymic method, but no detectable activity remained after chloramine-t treatment. 4. High concentration of pig insulin inhibited binding of labelled parathyroid hormone to plasma membranes and partially inhibited the hormone-sensitive adenylate cyclase activity in a crude kidney-cortex preparation. 5. EDTA enhanced and Ca(2+) inhibited binding of labelled parathyroid hormone to plasma membranes. 6. Whereas rat kidney homogenates were capable of degrading labelled parathyroid hormone to trichloroacetic acid-soluble fragments, neither crude homogenates nor purified membranes from bovine kidney showed this property. 7. Binding of parathyroid hormone is discussed in relation to metabolism and initial events in hormone action.

Adenylyl Cyclases↗
PubMed1980

The regulation of glucose and pyruvate formation from glutamine and citric-acid-cycle intermediates in the kidney cortex of rats, dogs, rabbits and guinea pigs.

The suppression by 3-mercaptopicolinate of gluconeogenesis from glutamine or 2-oxoglutarate in rat or dog kidney tubules did not affect the amount of these substrates undergoing complete oxidation. Furthermore, 3-mercaptopicolinate caused an accumulation of lactate in dog tubules. 3-Mercaptopicolinate abolished both gluconeogenesis and substrate oxidation in tubules from rabbit and guinea-pig kidney. These results imply the presence of an alternative pathway to phosphoenolpyruvate carboxykinase/pyruvate kinase for the production of pyruvate from citric-acid-cycle intermediates in the kidney cortex of rats and dogs but not in that of rabbits or guinea pigs. Oxaloacetate decarboxylase (present in the kidney cortex of all four species) or 'malic' enzyme (present in rat and dog but absent in rabbit and guinea-pig kidney cortex) could function in this role. Our observations indicate that 'malic' enzyme is probably implicated in this phenomenon. The lactate production observed in dog tubules in the presence of 3-mercaptopicolinate can be suppressed when aspartate formation is inhibited by 2-amino-4-methoxy-trans-but-3-enoic acid. This suggests that the provision of cytosolic NADH from citric-acid-cycle intermediates is facilitated by accumulation of aspartate acting as a 'sink' for cytosolic oxaloacetate.

Animals↗
PubMed1980

Triacylglycerol metabolism in isolated rat kidney cortex tubules.

Triacylglycerol metabolism has been studied in kidney cortex tubules from starved rats, prepared by collagenase treatment. Triacylglycerol was determined by a newly developed fully enzymic method. Incubation of tubules in the absence of fatty acids led to a decrease of endogenous triacylglycerol by about 50% in 1h. Addition of albuminbound oleate or palmitate resulted in a steady increase of tissue triacylglycerol over 2h. The rate of triacylglycerol synthesis was linearly dependent on oleate concentration up to 0.8mm, reaching a saturation at higher concentrations. Triacylglycerol formation from palmitate was less than that from oleate. This difference was qualitatively the same when net synthesis was compared with incorporation of labelled fatty acids. Quantitatively, however, the difference was less with the incorporation technique. Gluconeogenic substrates, which by themselves had no effect on triacylglycerol concentrations, stimulated neutral lipid formation from fatty acids. Glucose and lysine did not have such a stimulatory effect. Inhibition of gluconeogenesis from lactate by mercaptopicolinic acid likewise inhibited triacylglycerol formation. This inhibitory effect was seen with oleate as well as with oleate plus lactate. When [2-(14)C]lactate was used the incorporation of label into triacylglycerol was found in the glycerol moiety exclusively. Addition of dl-beta-hydroxybutyrate (5mm) to the incubation medium in the presence of oleate or oleate plus lactate led to a significant increase in triacylglycerol formation. In contrast with the gluconeogenic substrates, dl-beta-hydroxybutyrate had no stimulatory effect on fatty acid uptake. The results suggest that renal triacylglycerol formation is a quantitatively important metabolic process. The finding that gluconeogenic substrates, but not glucose, increase lipid formation, indicates that the glycerol moiety is formed by glyceroneogenesis in the proximal tubules. The effect of ketone bodies seems to be caused by the sparing action of these substrates on fatty acid oxidation. The decrease of triacylglycerol in the absence of exogenous substrates confirms previous conclusions that endogenous lipids provide fatty acids for renal energy metabolism.

Animals↗
PubMed1985

An azide-insensitive low-affinity ATPase stimulated by Ca2+ or Mg2+ in basal-lateral and brush border membranes of kidney cortex.

Basal-lateral and brush border membranes from pig kidney cortex were prepared by differential centrifugation followed by free-flow electrophoresis. In each type of membrane, azide-insensitive, low-affinity Ca2+-ATPase and Mg2+-ATPase activities are demonstrated. A comparative study for both membranes further reveals the following analogies between these ATPases: (a) they show maximal activity between pH 8 and 8.5; (b) they exhibit Km values for Ca-ATP or Mg-ATP in the millimolar range and have a comparable low substrate specificity; (c) they are insensitive to 10 microM of vanadate, N,N'-dicyclohexylcarbodiimide, e diethylstilbestrol, quercetin, harmaline and amiloride. The partial inhibition by 1 mM of the various compounds is rather aspecific. In view of these similarities it is concluded that only one enzyme entity is responsible for the activity which is measured in both membrane types. The HCO3-stimulated Mg2+-ATPase activity in pig kidney cortex was also studied. This enzyme, however, is clearly of mitochondrial origin since the HCO3-stimulation coincides with the distribution profile of succinate dehydrogenase, a mitochondrial marker; and since it is inhibited by azide.

Adenosine Triphosphatases↗
PubMed1991

Do rat kidney cortex microsomes possess the enzymatic machinery to desaturate and chain elongate fatty acyl-CoA derivatives?

Rat kidney cortex microsomal preparations were unable to catalyze delta 9, delta 6 and delta 5 desaturation of stearoyl-coenzyme A (CoA), linoleoyl-CoA and dihomo-gamma-linolenoyl-CoA, respectively. The kidney cortex microsomal fraction, however, did catalyze the malonyl-CoA dependent fatty acyl-CoA elongation. The biochemical properties of palmitoyl-CoA elongation were studied as a function of protein concentration, time, reduced nicotinamide adenine dinucleotide phosphate (NADPH), malonyl-CoA and substrate concentrations; of the substrates investigated, delta 6,9,12-18:3 was the most active. Unlike what was observed in the hepatic system, a high-carbohydrate, fat-free diet did not induce kidney fatty acid chain elongation. All intermediate kidney cortex microsomal reactions, i.e., beta-ketoacyl-CoA reductase, beta-hydroxyacyl-CoA dehydrase and trans-2-enoyl-CoA reductase activities, were significantly higher (greater than one order of magnitude) than the condensing enzyme activity, suggesting that the rate-limiting step in total elongation is the initial condensation reaction. Contrary to other reports, the results suggest that the kidney cannot synthesize arachidonic acid needed for eicosanoid production.

Acyl Coenzyme A↗
PubMed1975

Contribution of long chain fatty acids to the energy supply of the rat kidney cortex.

Tubular fragments from rat kidney cortex were isolated by collagenase and suspended in an incubation medium containing a combination of several renal substrates. Substrate concentrations were in the physiological range. O2 uptake, total CO2 production, and the 14CO2 production from U-14C-labeled palmitate and oleate were measured. During the first minutes of incubation the CO2 production from palmitate and oleate was 10.5% or 6.3%, respectively, of the total CO3 produced. The RQ was 0.897. A subsequent decrease of the total CO2 production at a constant uptake of oxygen indicated a rising contribution of fatty acids to the fuel of respiration. The renal preference for substrates other than longchain fatty acids is discussed.

Animals↗
PubMed1966

Formation of glucose from hexoses, pentoses, polyols and related substances in kidney cortex.

1. Slices of rat kidney cortex, on incubation in a saline medium, formed d-glucose from the following substances: d-fructose, d-galactose, d-mannose, l-sorbose, l-arabinose, d-xylose, glycerol, myo-inositol, l-iditol, sorbitol, xylitol, ribitol, methylglyoxal, dihydroxyacetone, l-glyceraldehyde, d-glyceraldehyde, dl-glyceraldehyde, dl-glycerate. Values for the rates of glucose formation from these precursors are given. 2. No glucose was formed from l-rhamnose, d-arabitol, d-arabinose, d-ribose, l-fucose, d-lyxose, mannitol, dulcitol, d-glucuronate, propane-1,2-diol and propan-2-ol. 3. The pathways of glucose formation from the various precursors are discussed (Scheme 1). 4. l-Glyceraldehyde inhibited the formation of glucose from d-glyceraldehyde.

Alcohols↗
PubMed1984

Tubular regeneration in rat kidney cortex during treatment with gentamicin at a low dose.

Tissue injury induced in rat kidney cortex by gentamicin at a low dose (10 mg/kg) has been studied by measuring subsequent regeneration after treatment for 4, 7, and 14 days. Cell proliferation was demonstrated by the incorporation of [3H]-thymidine into kidney cortex DNA. In treated animals, the specific radioactivity of DNA increased up to 4.6 times the mean value found in the controls. Autoradiography showed labelling of nuclei in proximal tubular cells. Electron microscopy showed that a subpopulation of tubular cells, devoid of myeloid bodies, which are characteristic of gentamicin intoxication, is also poorer in peroxisomes, and therefore may belong to less differentiated, regenerating cells. It is concluded that a low dose of gentamicin induces measurable tissue regeneration.

Animals↗
PubMed2006

Clathrin and clathrin-accessory proteins in rat kidney cortex epithelia.

Several vectorial transport routes in mammalian cells involve clathrin and associated proteins. In kidney epithelia urine production requires numerous transport processes. However, only little is known about the distribution of clathrin and its associated proteins in this organ in situ. We now report on the presence and distribution of clathrin and its accessory proteins AP1, AP2, Eps15, Epsin, CALM and Clint/EpsinR in the epithelia of the rat kidney cortex using immunoblotting, immunofluorescence and immuno-electron microscopy. Our data show that all investigated proteins are ubiquitously present in rat kidney cortex epithelia, however, with distinct distribution patterns. In the renal corpuscle, podocytes showed the most conspicuous labelling. Clathrin, AP2 and CALM were highly expressed in foot processes, while AP1 was primarily localized in the cell body. In the proximal tubule all proteins were present in dots along the plasma membrane and most conspicuous below the brush border. However, clathrin and AP2 co-localized in vesicle subtypes distinct from those containing clathrin and AP1. In the distal tubule and in the cortical collecting duct all proteins were found in the apex of the cells; however, AP1 and Clint/EpsinR showed additional staining in perinuclear dots. The occurrence and distribution of the investigated proteins in kidney epithelia are discussed with respect to their possible involvement in the functions of the specific nephron segment.

Adaptor Proteins, Vesicular Transport↗
PubMedDate not supplied

Gluconeogenesis in kidney cortex slices of the guinea pig. Its relation to acidosis and to calcium.

In contrast to rat kidney cortex the glucogenic capacity of kidney cortex slices from normally treated guinea pigs was very low. Reduction of the pH of the incubation medium by either lowering the HCO3-concentration or by increasing the pCO2 resulted only in varying stimulatory effects on glucose production from endogeneous or exogeneous sources. Considerable rates of net synthesis of glucose from lactate, pyruvate, malate, 2-oxoglutarate, glutamate, and glycerol--but not from glutamine--were only observed in kidneys from animals with prolonged metabolic acidosis. Neither in experiments with normally treated animals nor in those with acidotic guinea pigs the glucose production decreased, when calcium was omitted from the incubation medium. Though glutamine was not converted into glucose, it served as a substrate for ammoniagenesis. On the basis of the presented results it is concluded that species differences exist in the regulation of renal gluconeogenesis.

Acidosis, Renal Tubular↗