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At least 19 recordsLinked to original sources
PubMed1976

Properties of guanylate cyclase from rat kidney cortex and transplantable kidney tumors.

The subcellular distribution and properties of guanylate cyclase was examined in preparations of normal rat renal cortex and Morris renal tumors MK2 and MK3. In normal kidney cortex about two-thirds of guanylate cyclase activity of homogenates was found in soluble fractions. With renal tumors the homogenate activity was less and the enzyme was equally divided between particulate and soluble fractions. The particulate enzyme in kidney cortex and tumors was associated with all particulate fractions. Triton X-100 increased the activity of all preparations. All preparations preferred Mn2+ as the sole cation. The stimulatory effects of Ca2+ on soluble enzyme and inhibitory effects on particulate activity were similar with preparations of renal cortex and tumors. ATP inhibited all preparations. Soluble and particulate guanylate cyclases from renal cortex were activated several-fold with 1 mM NaN3. Preparations of tumor enzymes did not respond to NaN3. Thus, compared to normal renal cortex the subcellular distribution of guanylate cyclase and some of its properties are altered in preparations of renal tumors.

Animals↗
PubMed1975

Antagonism between parathyroid hormone and norepinephrine on cyclic adenosine-3':5'-monophosphate (cAMP) levels in isolated tubules from rat kidney cortex.

Isolated rat kidney cortex tubules were used as a model system to study the hormonal regulation of cyclic adenosine-3':5'-monophosphate (cAMP) levels in vitro. When incubated over 15 min, parathyroid hormone increased cAMP levels 4-fold in the absence of inhibitors of cAMP phosphodiesterase. Norepinephrine in a concentration of 5-10-7 M which had itself no effect on cAMP levels under this condition, inhibited the effect of parathyroid hormone by 50%. This effect of the catecholamines could be completely abolished by the addition of an alpha-receptor blocking agent, phentolamine. The addition of an inhibitor of cAMP phosphodiesterase, in a concentration sufficient to prevent the breakdown of extratubular cAMP, potentiated hormone effects on cAMP levels. The antagonism between catecholamines and parathyroid hormone on cAMP levels was however not abolished by this treatment. This indicated that catecholamines probably inhibited parathyroid hormone stimulated cAMP formation. Since most of the cAMP was found to be intratubular, it can be assumed that norepinephrine and parathyroid hormone interact in the same cell. Proximal tubular sodium reabsorption and renal gluconeogenesis are discussed as possible events of this hormone interaction.

Animals↗
PubMed1975

Effect of diuretics on ion transport of kidney cortex mitochondria. III. Species difference in calcium accumulation and in ethacrynic acid effect.

Effect of inorganic phosphate (4 X 10(-3) M) on Ca++-accumulation was examined in kidney cortex mitochondria. Ca++-accumulation of rat kidney cortex mitochondria was slightly influenced by inorganic phosphate. On the other hand, dog kidney cortex mitochondria did not accumulate calcium from the incubation medium until the inorganic phosphate had been added. Ca++-accumulation of rabbit kidney cortex mitochondria was markedly stimulated by inorganic phosphate. When ethacrynic acid was added to the reaction medium in the absence of inorganic phosphate, Ca++-accumulation of rat kidney cortex mitochondria was depressed and the decrease in calcium content of rabbit and dog kidney cortex mitochondria was enhanced. In the presence of inorganic phosphate, the inhibition of Ca++-accumulation by ethacrynic acid was observed only on dog kidney cortex mitochondria. Subsequently, the effect of inorganic phosphate (4 X 10(-4) M) and ethacrynic acid (1 X 10(-4) M on Ca++-ATPase was examined in kidney cortex mitochondria. The low concentration of inorganic phosphate (4 X 10(-4) M) activated Ca++-ATPase of kidney cortex mitochondria in all animal species. The greatest activation of Ca++-ATPase occurred in rabbits, but the activity of the enzyme was lower than that in rats and dogs. Inhibition of Ca++-ATPase by ethacrynic acid was depressed by the addition of inorganic phosphate in kidney cortex mitochondria of experimental animals. Ca++-accumulation may be regulated through the stimulating effect of inorganic phosphate and the inhibitory effect of ethacrynic acid on Ca++-ATPase in kidney cortex mitochondria. Species difference in ethacrynic acid effect on Ca++-accumulation in kidney cortex mitochondria of rats, rabbits and dogs is discussed.

Adenosine Triphosphatases↗
PubMedDate not supplied

[Low temperature and cryoprotectant effect on oxygen uptake in rat kidney cortex homogenates].

Respiration and oxidative phosphorylation of the rat kidney cortex mitochondria are studied as affected by low temperatures and cryoprotectants. There is no change in respiration in state 2 during freezing and thawing of the rat kidney cortex slices both in case of using the succinate oxidation substrate and alpha-ketoglutarate. Respiration in state 3 is inhibited in the medium with alpha-ketoglutarate during freezing under protection of polyethylene oxide-100 (PEO-100) and glycerol, and does not significantly change in case of using dimethyl sulphoxide (DMSO). The effectiveness of cryoprotectants used in the experiments reduces in the following sequence: DMSO--glycerol--PEO-100. Preservation of the main mitochondria function, ATP synthesis, is shown to be possible for the kidney cortex slices exposed to freezing and thawing.

Adenosine Triphosphate↗
PubMed1975

Fatty acid hydroxylation in rat kidney cortex microsomes.

Rat kidney microsomes have been found to catalyze the hydroxylation of medium-chained fatty acids to the omega- and (omego-1)-hydroxy derivatives. This reaction, which requires NADPH and molecular oxygen, is a function of monooxygenase system present in the kidney microsomes, containing NADPH-cytochrome c reductase and cytochrome P-450K. NADH is about half as effective as an electron donor as NADPH and there is an additive effect in the presence of both nucleotides. Cytochrome P-450K absorbs light maximally at 452-3 nm, when it is reduced and bound to carbon monoxide. The extinction coefficient of this complex is 91 mM(-1) cm(-1). Electrons from NADPH are transferred to cytochrome P-450K via the NADPH-cytochrome c reductase. The reduction rate of cytochrome P-450K is stimulated by added fatty acids and the reduction kinetics reveal the presence of endogenous substrates bound to cytochrome P-450K. Both cytochrome P-450K concentration and fatty acid hydroxylation activity in kidney microsomes are increased by starvation. On the other hand, phenobarbital treatment of the rats has no effect on either the hemoprotein or the overall hydroxylation reaction and 3,4-benzpyrene administration induces a new species of cytochrome P-450K not involved in fatty acid hydroxylation. Cytochrome P-450K shows, in contrast to liver P-450, high substrate specificity. The only substances forming enzyme-substrate complexes with cytochrome P-450K are the medium-chained fatty acids and certain derivatives of these acids. The chemical requirements for substrate binding include a carbon chain of medium length and at the end of the chain a carbonyl group and a free electron pair on a neighbouring atom. The distance between the binding site for the carbonyl group and the active oxygen is suggested to be in the order of 16 A. This distance fixes the ratio of omega- and (omega-1)-hydroxylated products formed from a certain fatty acid by the single species of cytochrome P-450K involved. The membrane microenvironment seems also to be of importance for the substrate specificity of cytochrome P-450K, since removal of the cytochrome from the membrane lowers its binding specificity to some extent. A comparison between the liver and kidney cytochrome P-450 systems suggests that the kidney cytochrome P-450K system is specialized for fatty acid hydroxylation.

Animals↗
PubMed1975

[An enzymatic method for the isolation of tubules and cells from human kidney cortex].

The isolation of tubules and cells from human kidney cortex was realized by an enzymatic method. Tubules and cells were released from slices of kidney cortex by collagenase. The yield amounted to 80 % of the wet weight of incubated cortex slices. Thus numerous experiments with isolated tubules from one organ could be performed. Glucose production from different substrates was measured in order to test the biochemical integrity of the isolated cells. The highest rates of glucose formation were obtained with fructose as precursor. Glucose production was higher from lactate than from pyruvate. With proline and glutamine as substrates only small amounts of glucose were produced. Glucose formation from 10 mmol/1 pyruvate was linear with time up to 80 minutes. Ado-3':5'-P stimulated glucose formation at 10 mumolar concentration and inhibited gluconeogenesis at 1 mmolar, 0.1 mmolar and 1 mumolar concentrations.

Calcium↗
PubMed1977

Catabolism of 6-ketoprostaglandin F1alpha by the rat kidney cortex.

Homogenates of the rat kidney cortex converted 5,8,9,11,12,14,15-hepta-tritiated 6-ketoprostaglandin F 1alpha into one major product identified by gas chromatography-mass spectrometry of the methoxime-methyl ester trimethylsilyl ether derivative as 6,15-diketo-9,11-dihydroxyprost-13-enoic acid. The sequence of derivatisation i.e. methoximation prior to methylation, was crucial as methylation of 15-keto catabolites of the E, F and 6-keto-F series affords degradation products. The corresponding 15-keto-13,14-dihydro catabolite was formed in much smaller quantities. Time course studies indicated that 6-keto-prostaglandin F1alpha was catabolised at a slower rate (about 2-5 fold) than prostaglandin F1alpha. The catabolic activity was blocked by NADH.

Animals↗
PubMed1976

Tridimensional ultrastructure of freeze-fractured rat kidney cortex (studied in stereo).

The tridimensional ultrastructure of the inner cortex of rat kidney has been studied by observing freeze-fractured tissue in stereo. The complex structure of the tubules, fenestrated capillaries and glomeruli is more readily observed through the irregular fracturing of the tissue that occurs in this technique. The ultrastructure of the brush border and interdigitating membranes of the proximal tubules, the structure of the fenestrated endothelial membranes of the capillaries and the ribbon-like appearance of the filtration space between the foot processes of the glomeruli were especially well depicted in stereo images of freeze-fractured renal tissue.

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↗
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↗
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↗
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↗
PubMed1977

Prolyl 3-hydroxylase: partial characterization of the enzyme from rat kidney cortex.

The formation of 3-hydroxyproline was studied with crude rat kidney cortex extract as a source of enzyme and chick embryo tendon protocollagen and procollagen or cartilage protocollagen as a substrate. Synthesis of 3-hydroxyproline was observed with all these substrates and the formation of 3-hydroxyproline ranged up to seven residues per pro-alpha-chain. The highest rate of 3-hydroxylation took place at 20 degrees C and the reaction required Fe2+, O2,2-oxoglutarate and ascorbate. The formation of 3-hydroxyproline was affected by chain length and the conformation of the substrate, in that longer polypeptide chains proved better substrates, while the native triple-helical conformation of protocollagen or procollagen completely prevented the reaction. Formation of 3-hydroxyproline with tendon procollagen as a substrate was not inhibited by antiserum to prolyl 4-hydroxylase or by poly(L-proline) when these substances were used in concentrations which clearly inhibited 4-hydroxyproline formation with tendon protocollagen as a substrate. Furthermore, pure prolyl 4-hydroxylase did not synthesize any 3-hydroxyproline under conditions in which the crude rat kidney cortex enzyme would readily do so. The data thus strongly suggest that prolyl 3-hydroxylase and prolyl 4-hydroxylase are separate enzymes.

Animals↗
PubMedDate not supplied

[Effect of starvation and diabetes on the activity of glucose-6-phosphate and 6-phosphogluconate dehydrogenases and on the free fatty acid content of rat kidney cortex and medulla].

Activity of dehydrogenases related to pentosephosphate pathway was not distinctly altered in soluble fraction of kidney cortex and medulla after 48 and 72 hrs of starvation. In diabetes the activity of these enzymes in rat kidney, as distinct from liver tissue, was not decreased but it was elevated and within 72 hrs after administration of alloxan the activity of glucose-6-phosphate dehydrogenase was increased 2-fold and the activity of 6-phosphogluconate dehydrogenase was increased by 30% above the normal level. Content of free fatty acids was also increased in kidney cortex of diabetic rats within 72 hrs after administration of alloxan. Alterations in content of free fatty acids were not observed either in kidney of diabetic animals within other studied periods (6 and 14-16 days) of treatment or in the tissue of starved rats. The data obtained suggest that free fatty acids do not participate immediately in controlling effect on dehydrogenases of pentosephosphate pathway in kidney in vivo.

Animals↗
PubMed1975

Isolation of peroxisomes from the dog kidney cortex.

The present study was undertaken to separate peroxisomes of the dog kidney cortex by the methods of discontinuous sucrose density gradient and zonal centrifugation. The separation of subcellular particles was evaluated by measuring the activities of reference enzymes, beta-glycerophosphatase for lysosomes, succinate dehydrogenase for mitochondria, glucose-6-phosphatase for microsomes, and catalase and D-amino acid oxidase for peroxisomes. The activities of D-amino acid oxidase and catalase were mainly observed in fractions 1 and 2 (1.6 and 1.7 M sucrose) obtained by discontinuous sucrose density-gradient centrifugation. Small amounts of acid phosphatase and succinate dehydrogenase contaminated these fractions. Considerably higher activity of catalase was determined in the supernatant, while D-amino acid oxidase showed a lower activity. By the method of zonal centrifugation, the highest specific activities of catalase and D-amino acid oxidase were found in fraction 50 (1.73 M sucrose) with no succinate dehydrogenase, acid phosphatase or glucose-6-phosphatase activity. These results suggested that peroxisomes of dog kidney cortex were clearly separated in 1.73 M sucrose from mitochondria, lysosomes and microsomes by zonal centrifugation.

Animals↗
PubMed1976

Phosphatidylinositol kinase and diphosphoinositide kinase of rat kidney cortex: properties and subcellular localization.

The properties of phosphatidylinositol kinase and diphosphoinositide kinase from rat kidney cortex were studied. The enzymes were completely Mg2+-dependent. Cutscum detergent activated phosphatidylinositol kinase, but diphosphoinositide kinase was inhibited by all detergents tested. The pH optima were 7.7 for phosphatidylinositol kinase and 6.5 for diphosphoinositide kinase. On subcellular fractionation of kidney-cortex homogenates by differential centriflgation, the distribution of phosphatidylinositol kinase resembled that of the marker enzymes for brush-border, endoplasmic-reticulum and Golgi membranes. Diphosphoinositide kinase distribution resembled that of thiamin pyrophosphatase (assayed in the absence of ATP), diphosphoinositide phosphatase and triphosphoinositide phosphatase. Activities of both kinases were low in purified brush-border fragments. Diphosphoinositide kinase is probably localized in the Golgi complex.

Adenosine Triphosphate↗
PubMed1977

Studies of binding of parathyroid hormone to a detergent-dispersed preparation from bovine kidney cortex plasma membranes.

Bovine kidney plasma membranes containing parathyroid hormone-sensitive adenylate cyclase activity were dispersed with 1% Triton X-100 and centrifuged at 150,000 X g for 2 h. Approximately 40% of the total membrane protein was extracted by this procedure. The extraction greatly reduces the fluoride-stimulated and the parathyroid hormone-sensitive adenylate cyclase activity of the membranes and yields a supernatnat which binds biologically active, tritiated parathyroid hormone. Hormone binding is stable for up to 15 h and has a linear dependence on protein concentration in the extract. Binding of the labeled hormone at concentrations of 5 to 10 nM is inhibited by preincubation with unlabeled min, and displays a dependence on temperature, time, and pH. Binding specificity is maximal at physiological pH, being inhibited by only the native hormone or its synthetic 1-34 NH2-terminal, biologically active fragment. Binding increases dramatically at pH 6.0, but is nonspecific in character. Half-maximal inhibition of the binding was achieved at 3.2 X 10(-7) M concentrations of the native hormone and 5.0 X 10(-7) M concentrations of the synthetic 1-34 NH2-terminal fragment. Calcium does not inhibit either total or specific binding. Inhibition, kinetic, and pH dependence data suggest that the extracted component(s) represent the parathyroid hormone binding protein(s) formerly identified in particulate membrane preparations.

Animals↗