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PubMed1995

Localization of dihydroorotate oxidase in myocardium and kidney cortex of the rat. An electron microscopic study using the cerium technique.

Biochemical studies have demonstrated that dihydroorotate dehydrogenase (DHOdehase; EC 1.3.3.1 or 1.3.99.11) is the sole enzyme of de novo pyrimidine synthesis in mitochondria, whereas the rest of the pathway takes place in the cytosol. The dehydrogenation of dihydroorotate to orotate is linked to the respiratory chain via ubiquinone. In this study, we show for the first time the ultrastructural localization of DHOdehase. Since the purified enzyme was found to act both as dehydrogenase and as oxidase, the cerium capture technique for detecting enzymatically generated hydrogen peroxide could be applied to pin-point the in situ activity of DHOdehase oxidase in mitochondria of rat heart and kidney cortex. Cerium perhydroxide as the final reaction product was detected predominantly in the matrix with some focal condensation along the inner membrane, but not in the intermembrane space. From this pattern of localization, it is concluded that the active site of the membrane-bound enzyme could face the mitochondrial matrix similar to succinate dehydrogenase. The reliability of the applied method for the demonstration of DHOdehase oxidase was demonstrated by the addition of Brequinar sodium to the incubation medium. This quinoline-carboxylic acid derivative is a potent inhibitor of DHOdehase and has proven anti-proliferative activity. The present observations do not ascertain whether the oxidase is permanently active as a constant portion of the enzyme in vivo, similar to xanthine oxidase/dehydrogenase. However, DHOdehase should be considered as a source of radical oxygen species under pathophysiological conditions.

Animals↗
PubMed1998

Ultrastructural characterization of atrial natriuretic peptide receptors (ANP-R) mRNA expression in rat kidney cortex.

Atrial natriuretic peptide (ANP) and two complementary peptides named brain natriuretic peptide and C-type natriuretic peptide are involved in diuresis, natriuresis, hypotension and vasorelaxation. Their actions are mediated by highly selective and specific ANP receptors. Three subtypes have been characterized and cloned: ANP receptor A, -B and -C. In the present study, the mRNA for each subtype was detected by ultrastructural in situ hybridization on ultrathin sections of Lowicryl-embedded tissue and frozen tissue. The distribution of mRNA (visualized by gold particles) for each subtype was found to differ in different cells of the nephron. The three subtypes of this receptor family were expressed in all the parts of the nephron, but their expression levels were different. The ANPR-A mRNA was the most abundant in cells of glomerulus, proximal and distal tubules. The subtype C was the least expressed mRNA in glomerulus. In contrast, the subcellular localization of the three mRNAs was similar; they were found in the cytoplasmic matrix and the euchromatin of the nucleus. In conclusion, the differential expression of these mRNAs in kidney cortex indicates that these three peptides act directly in differing parts of nephron regions which are the glomerulus, the proximal and distal tubules.

Animals↗
PubMed1981

Isoprenaline-induced secretion of active and inactive renin in anaesthetized rabbits and by kidney cortex slices.

1. The effect of the beta-adrenoceptor agonist isoprenaline on the secretion of active and inactive renin was investigated in two preparations. 2. In ten urethane-anaesthetized rabbits isoprenaline, given as a renal artery infusion, had relatively minor effects on renal sodium excretion (increased) and systemic arterial blood pressure (decreased). Urine volume, potassium excretion, creatinine clearance and serum electrolytes were all unchanged. Plasma active and inactive renin both increased immediately and returned to basal values after ceasing the isoprenaline infusion. 3. No significant changes in either plasma renin activity or renal function were observed in a group of ten control animals. 4. The magnitude of the isoprenaline-induced changes in plasma active renin was similar to that in a previous study of frusemide diuresis, but the time course was quite different. Inactive renin disappeared from plasma during frusemide diuresis. 5. Renin release by rabbit kidney cortex slices was also studied. Isoprenaline, added to the incubation medium, caused a dose-related increase in active renin secretion, but inactive renin release remained unchanged. This is in marked contrast to a previous study where reducing [Na+] increased active renin and inhibited inactive renin output. 6. These data support our previous suggestion that activation of inactive renin is regulated by a sodium-sensitive intrarenal mechanism.

Animals↗
PubMed1994

A small artery heat transfer model for self-heated thermistor measurements of perfusion in the kidney cortex.

A small artery model (SAM) for self-heated thermistor measurements of perfusion in the canine kidney is developed based on the anatomy of the cortex vasculature. In this model interlobular arteries and veins play a dominant role in the heat transfer due to blood flow. Effective thermal conductivity, kss, is calculated from steady state thermistor measurements of heat transfer in the kidney cortex. This small artery and vein model of perfusion correctly indicates the shape of the measured kss versus perfusion curve. It also correctly predicts that the sinusoidal response of the thermistor can be used to measure intrinsic tissue conductivity, km, in perfused tissue. Although this model is specific for the canine kidney cortex, the modeling approach is applicable for a wide variety of biologic tissues.

Animals↗
PubMed1972

Studies on the mechanism of action of angiotensin on ion transport by kidney cortex slices.

1. A study has been made of the effects of cyclic AMP, phosphodiesterase inhibitors and protein synthesis inhibitors on the response of rat kidney cortex slices to physiological doses of angiotensin.2. The additions of cyclic AMP, dibutyryl cyclic AMP and/or phosphodiesterase inhibitors to the incubation medium (conditions which would be expected to increase intracellular cyclic AMP levels) were without effect on sodium or potassium transport by kidney slices.3. Actinomycin D (an inhibitor of the transcription stage of protein synthesis), at concentrations which inhibit RNA synthesis by 75%, has no effect on either control or angiotensin stimulated sodium transport.4. Cycloheximide or puromycin (inhibitors of the translation stage of protein synthesis), at concentrations which inhibit protein synthesis by 70-80%, have no effect on control sodium and potassium transport by kidney slices, but completely block the angiotensin stimulation of these processes.5. These findings are discussed in relation to the possible involvement of cyclic AMP and protein synthesis in the mechanism of action of angiotensin on kidney sodium and potassium transport.

Angiotensin II↗
PubMed1983

Stimulation of glutamine metabolism by 3-aminopicolinate in isolated dog kidney-cortex tubules.

1. The effects of 3-aminopicolinate, a known hyperglycaemic agent in the rat, on glutamine metabolism were studied in isolated dog kidney tubules. 2. 3-Aminopicolinate greatly stimulated glutamine (but not glutamate) removal and glutamate accumulation from glutamine as well as formation of ammonia, aspartate, lactate, alanine and glucose. 3. The increased accumulation of aspartate from glutamine and glutamate, and the inhibition of glucose synthesis from various non-nitrogenous gluconeogenic substrates, as well as the increased accumulation of malate from succinate, support the proposal that 3-aminopicolinate is an inhibitor rather than a stimulator of phosphoenolpyruvate carboxykinase (EC 4.1.1.32) in dog kidney tubules. 4. With glutamine as substrate, the increase in flux through glutamate dehydrogenase (EC 1.4.1.3) could not explain the large increase in glutamine removal caused by 3-aminopicolinate. 5. Inhibition by amino-oxyacetate of accumulation of aspartate and alanine from glutamine caused by 3-aminopicolinate did not prevent the acceleration of glutamine utilization. 6. These data are consistent with a direct stimulation of glutaminase (EC 3.5.1.2) by 3-aminopicolinate in dog kidney tubules.

Aminooxyacetic Acid↗
PubMed1975

Transport ATPase cytochemistry: ultrastructural localization of potassium-dependent and potassium-independent phosphatase activities in rat kidney cortex.

A cytochemical method for the light and electron microscope localization of the K- and Mg-dependent phosphatase component of the Na-K-ATPase complex was applied to rat kidney cortex, utilizing p-nitrophenylphosphate (NPP) as substrate. Localization of K-N-ATPase activity in kidneys fixed by perfusion with 1% paraformaldehyde -0.25% glutaraldehyde demonstrated that distal tubules are the major cortical site for this sodium transport enzyme. Cortical collecting tubules were moderately reactive, whereas activity in proximal tubules was resolved only after short fixation times and long incubations. In all cases, K-NPPase activity was restricted to the cytoplasmic side of the basolateral plasma membranes, which are characterized in these neplron segments by elaborate folding of the cell surface. Although the rat K-NPPase appeared almost completely insensitive to ouabain with this cytochemical medium, parallel studies with the more glycoside-sensitive rabbit kidney indicated that K-NPPase activity in these nephron segments is sensitive to this inhibitor. In addition to K-NPPase, nonspecific alkaline phosphatase also hydrolyzed NPP. The latter could be differentiated cytochemically from the specific phosphatase, since alkaline phosphatase was K-independent, insensitive to ouabain, and specifically inhibited by cysteine. Unlike K-NPPPase, alkaline phosphatase was localized primarily to the extracellular side of the microvillar border of proximal tubules. A small amount of cysteine-sensitive activity was resolved along peritubular surfaces of proximal tubules. Distal tubules were unreactive. In comparative studies, Mg-ATPase activity was localized along the extracellular side of the luminal and basolateral surfaces of proximal and distal tubules and the basolateral membranes of collecting tubules.

Adenosine Triphosphatases↗
PubMed2005

Contribution of L-3,4-dihydroxyphenylalanine metabolism to the inhibition of gluconeogenesis in rabbit kidney-cortex tubules.

The circulating L-3,4-dihydroxyphenylalanine, the drug of choice in the therapy of Parkinson's disease (PD), is efficiently extracted by kidney and converted to dopamine, known to control several renal functions. As: (i) in addition to liver, kidney is an important source of glucose in mammals and (ii) the action of this drug on renal gluconeogenesis has not yet been studied, the aim of the present investigation was to estimate the influence of L-3,4-dihydroxyphenylalanine metabolism on glucose formation in isolated kidney-cortex tubules incubated with various gluconeogenic substrates. The data indicate that a rapid intracellular degradation of L-3,4-dihydroxyphenylalanine and tyramine (at 100 and 200 microM concentrations) is accompanied by 25-40% decrease in glucose production from pyruvate, alanine + glycerol + octanoate and dihydroxyacetone due to augmented generation of hydrogen peroxide via monoamine oxidase B, resulting in a decline of glutathione redox state by 40%. Moreover, following inhibition of monoamine oxidase B by deprenyl or substitution of pyruvate by aspartate + glycerol + octanoate both L-3,4-dihydroxyphenylalanine and tyramine affect neither the rate of gluconeogenesis nor glutathione redox state. In view of: (i) L-3,4-dihydroxyphenylalanine- and tyramine-induced changes in intracellular levels of gluconeogenic intermediates, and (ii) a significant decline of phosphoenolpyruvate carboxykinase activity by 500 microM oxidized glutathione, it is likely that L-3,4-dihydroxyphenylalanine- and tyramine-evoked disturbances in the glutathione redox state might diminish flux through phosphoenolpyruvate carboxykinase and in consequence decrease glucose formation in renal tubules, suggesting a new potential side-action of L-3,4-dihydroxyphenylalanine treatment.

Alanine↗
PubMed1987

Neonatal rabbit kidney cortex in culture as tool for the study of collecting duct formation and nephron differentiation.

By stripping off the capsula fibrosa of neonatal rabbit kidneys a consistently thin tissue layer consisting of collecting duct anlagen, S-shaped bodies and nephrogenic blastema is obtained. This thin layer seems to be an excellent object for investigation of epithelium formation and nephron differentiation. Three different tissue culture protocols are described: 1. A polarly differentiated collecting duct epithelium with 'tight' characteristics consisting only of principal cells, grown on specific renal support 2. A morphologically dedifferentiated collecting duct principal cell monolayer grown on the unspecific bottom of a plastic culture dish 3. An embryonic tissue layer with numerous S-shaped bodies which might be a suitable model for investigation of the development of maturing nephron structures in serum-free culture medium.

Animals↗
PubMed1989

Maintenance of proximal and distal cell functions in SV40-transformed tubular cell lines derived from rabbit kidney cortex.

This paper reports the preparation and describes the properties of three renal tubular cell lines derived using SV40 infection of primary cultures of rabbit kidney cortical cells, enriched in proximal cells. RC.SV1 was initially derived from cultures grown in the presence of fetal calf serum exhibiting a low degree of proximal differentiation. The cells were subsequently adapted to grow in serum-free hormonally defined medium and display basic properties of proximal tubule cells including well-developed apical microvilli, strong expression of brush-border hydrolases, Na+-coupled glucose uptake, and increased cyclic AMP production when exposed to PTH. The other two cell lines were derived from cultures in serum-free hormonally defined medium and propagated in the same medium. They are characterized by some common properties including rare and short microvilli, low expression of apical hydrolases, and low or undetectable Na+-dependent glucose uptake, but differ by their abilities to respond by an increase in cAMP to various hormonal stimuli. RC.SV2 cells are sensitive to calcitonin and to a lesser extent to isoproterenol and PTH, suggesting that they may originate from the thick ascending limb of Henle's loop and the bright portion of the distal tubule. RC.SV3 responds essentially to isoproterenol and arginine vasopressin, suggesting a more distal origin (late distal and initial collecting tubule). Emergence of distal cell lines from cultures exhibiting proximal characteristics may be related to distal cell overgrowth as suggested by analysis of growth kinetics and increased Na+/H+ exchanger activity in RC.SV2 compared with RC.SV1.

Animals↗
PubMed1989

Isolation of two distinct populations of cells from rat kidney cortex and their use in the study of chemical-induced toxicity.

Procedures for the isolation and enrichment of cell populations from suspensions of rat kidney cortical cells were developed. Using Percoll density-gradient centrifugation, two populations of cells were obtained; marker enzymes [alkaline phosphatase and gamma-glutamyltransferase for proximal tubular (PT) cells and hexokinase for distal tubular (DT) cells] and functional responses (stimulation of PT cell oxygen consumption by succinate and inhibition of DT cell oxygen consumption by amiloride) were then employed to identify and assess the purity of the two fractions. The PT cell fraction was estimated to contain 97% PT cells and the DT cell fraction was estimated to contain 88% DT cells. Staining with toluidine blue and light microscopy showed that PT cells contained a brush border, were larger than DT cells, and had more intensely staining nuclei than DT cells. To demonstrate the usefulness of these cell preparations in the study of biochemical mechanisms of renal cell injury, time- and concentration-dependent effects of the PT cell-specific nephrotoxin cephaloridine (CPH) on PT and DT cell trypan blue exclusion were examined. CPH was toxic in PT cells but not in DT cells; viability of PT cells incubated with 0.1 or 1 mM CPH for 2 h was 57 or 34%, respectively, compared to 81% for control cells; viability of DT cells incubated with 0.1 or 1 mM CPH for 2 h was 74 or 71%, respectively, compared to 74% for control cells. This method thus provides highly enriched preparations of freshly isolated PT and DT cells that retain their unique properties and are suitable for studies of biochemical mechanisms of chemical toxicity and nephron heterogeneity.

Animals↗
PubMed1977

Binding of tritiated bovine parathyroid hormone to plasma membranes from bovine kidney cortex.

A membrane fraction enriched in parathyroid hormone (PTH)-sensitive adenylate cyclase and sodium and potassium ion-activated (Na+, K+)-ATPase was prepared from bovine kidney. Tritiated PTH binding to this membrane fraction was dependent on both hormone and membrane protein concentration. Both total and specific binding of the hormone decreased significantly after 5 to 10 min of incubation at 22 degrees. PTH binding was highly specific, being sensitive to inhibition only with active forms of unlabeled hormone (native and 1-34 PTH). Specific binding showed a pH optimum of 7.3 to 7.5. Inhibition of binding of tritiated hormone by unlabeled PTH was also highly effective at pH 6.0, but this apparently specific binding was also inhibited by adrenocorticotropic hormone, insulin, glucagon, and vasopressin. Dissociation of bound hormone was demonstrated, and an apparent dissociation constant of 4.6 X 10(-2) min-1 was obtained. Specific binding was eliminated by pretreatment of the membranes with trypsin. The concentration dependence for inhibition of binding with unlabeled PTH was identical to that for activation of adenylate cyclase in this membrane preparation, and binding was also inhibited by concentrations of calcium in the 0.5 to 2 mM range.

Adenylyl Cyclases↗
PubMed1991

Na(+)-ATPase activity, cell ion and water contents of kidney cortex slices from rats on a high Na+ diet.

Rats chronically fed for 15 months with an isotonic NaCl solution show a volume increase of their kidney proximal tubular cells as well as of the ouabain-insensitive, Na-stimulated ATPase activity of basolateral plasma membranes from these cells. If the experimental rats are changed to tap water after 15 months of the high sodium diet, the results are partially reversed. Thus, the cell volume and the Na-ATPase activity of their basolateral plasma membranes decrease, reaching values closer to those of control rats. There is more Na+ and Cl- in the cells from rats under the high Na(+)-diet than in the cells from control rats. On the other hand, when the rats on the high sodium diet are changed to control conditions (drinking tap water), their Na+ and Cl- contents decrease, approaching control values. It is proposed that the Na-ATPase activity is modulated "in vivo" by the cell volume.

Animals↗
PubMed1991

Cisplatin-induced injury to calcium uptake by mitochondria in glutathione-depleted slices of rat kidney cortex.

Changes in functional activities of mitochondria from kidney cortical slices incubated with cisplatin and the glutathione depletor diethylmaleate were examined. Diethylmaleate, which decreased the glutathione level in the slices, enhanced the cisplatin-induced decreases in glutathione level and calcium uptake in the mitochondria. The movement of cisplatin into mitochondria in the slices was not affected by diethylmaleate. These results suggest that the depressions in glutathione level and calcium uptake by cisplatin in mitochondria are enhanced by a decrease in cytoplasmic glutathione.

Animals↗