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PubMed1996

Megalin-mediated endocytosis of transcobalamin-vitamin-B12 complexes suggests a role of the receptor in vitamin-B12 homeostasis.

Kidney cortex is a main target for circulating vitamin B12 (cobalamin) in complex with transcobalamin (TC). Ligand blotting of rabbit kidney cortex with rabbit 125I-TC-B12 and human TC-57Co-B12 revealed an exclusive binding to megalin, a 600-kDa endocytic receptor present in renal proximal tubule epithelium and other absorptive epithelia. The binding was Ca2+ dependent and inhibited by receptor-associated protein (RAP). Surface plasmon resonance analysis demonstrated a high-affinity interaction between purified rabbit megalin and rabbit TC-B12 but no measurable affinity of the vitamin complex for the homologous alpha 2-macroglobulin receptor (alpha 2MR)/low density lipoprotein receptor related protein (LRP). 125I-TC-B12 was efficiently endocytosed in a RAP-inhibitable manner in megalin-expressing rat yolk sac carcinoma cells and in vivo microperfused rat proximal tubules. The radioactivity in the tubules localized to the endocytic compartments and a similar apical distribution in the proximal tubules was demonstrated after intravenous injection of 125I-TC-B12. The TC-B12 binding sites in the proximal tubule epithelium colocalized with megalin as shown by ligand binding to cryosections of rat kidney cortex, and the binding was inhibited by anti-megalin polyclonal antibody, EDTA, and RAP. These data show a novel nutritional dimension of megalin as a receptor involved in the cellular uptake of vitamin B12. The expression of megalin in absorptive epithelia in the kidney and other tissues including yolk sac and placenta suggests a role of the receptor in vitamin B12 homeostasis and fetal vitamin B12 supply.

Animals↗
PubMed1974

Role of cyclic adenosine 3':5'-monophosphate in the action of 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane (DDT)on hepatic and renal metabolism.

The possibility whether alterations in the cyclic AMP-adenylate cyclase-phosphodiesterase system play a role in the action of 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane (DDT) on hepatic and renal carbohydrate metabolism was investigated. Administration of exogenous cyclic AMP (10mg/100g) was found to mimic the action of DDT which enhanced the activities of pyruvate carboxylase, phosphoenolpyruvate carboxylase, fructose 1,6-diphosphatase and glucose 6-phosphatase in both liver and kidney cortex, elevated the concentration of blood glucose and urea and decreased the amount of hepatic glycogen. Treatment with theophylline augmented the effects of a submaximal dose of this halogenated hydrocarbon on serum urea and glucose as well as the key gluconeogenic enzymes in liver and kidney cortex. Addition of DDT in vitro to liver and kidney homogenates resulted in a significant enhancement of adenylate cyclase activity. Hepatic and renal slices from rats already treated with DDT displayed an increased ability to convert [(3)H]adenosine into cyclic [(3)H]AMP. Whereas kidney-cortex slices excised from rats given caffeine and DDT produced an even greater amount of cyclic [(3)H]AMP, imidazole, propranolol and hydrazine prevented the insecticide-stimulated rise in cyclic nucleotide production. In contrast, prostaglandin E(1) failed to exert any significant effect on DDT-induced increases in cyclic [(3)H]AMP synthesis from radioactive adenosine. The present study and our previous findings (Kacew & Singhal, 1973e) support the concept that the DDT-induced alterations in carbohydrate metabolism of liver and kidney cortex may be related to an initial stimulation of the cyclic AMP-adenylate cyclase system in these tissues.

Adenosine↗
PubMed1985

Surface densities of diaphragmed fenestrae and transendothelial channels in different murine capillary beds.

Fenestrated capillaries are provided with two types of regular discontinuities: fenestrae with negatively charged diaphragms, and transendothelial channels fitted with two diaphragms, of which the luminal one is uncharged. These structures are expected to affect macromolecular exchanges on the basis of size and charge. We have detected variations in the surface density of fenestrations and transendothelial channels (normalized to 1 micron of capillary endothelial profiles in sections) in selected areas of different murine organs, i.e., kidney cortex, duodenal mucosa, and exocrine pancreas. The survey was limited to endothelial segments less than or equal to 400 nm thick, and covered a total length of endothelial profiles of 1180 microns, 730 microns, and 1189 microns in the exocrine pancreas, intestinal mucosa, and kidney cortex, respectively. At least 1000 transendothelial openings were recorded by scoring for easily recognizable fenestrations, transendothelial channels, and unknowns, the latter representing either of the above in grazing sections. The linear density of all transendothelial openings taken together was found to vary among the different capillary beds (kidney cortex greater than intestinal mucosa greater than exocrine pancreas). This same sequence was observed for the linear densities of fenestrations, transendothelial channels, and unknowns considered individually. The values obtained were as follows: kidney cortex, 1.35 fenestrations per micron, 0.25 transendothelial channels per micron, 0.52 unknowns per micron; intestinal mucosa, 0.92 fenestrations per micron, 0.10 transendothelial channels per micron, 0.38 unknowns per micron; exocrine pancreas, 0.58 fenestrations per micron, 0.04 transendothelial channels per micron, 0.27 unknowns per micron. The differences in distribution of transendothelial openings among fenestrated capillary beds probably reflect capillary permeability modulations connected with the functions of these various organs.

Animals↗
PubMed2006

Divalent metal transporter 1 in the kidney proximal tubule is expressed in late endosomes/lysosomal membranes: implications for renal handling of protein-metal complexes.

The H+-coupled polyligand transport protein divalent metal transporter 1 (DMT1) plays a key role in mammalian iron homeostasis. It has a widespread pattern of expression including tissues associated with iron acquisition and storage. Interestingly, it is also highly expressed in the kidney, yet its function in this tissue is unknown. The aim of this study was to determine the cellular location of DMT1 in proximal tubule cells as a first step to determining the role of this protein in the kidney. To do this we performed RT-PCR and immunostaining experiments using rat kidney and the S1 proximal tubule-derived WKPT-0293 Cl.2 cell line. RT-PCR revealed that mRNAs encoding all four DMT1 splice variants were present in RNA extracted from rat kidney cortex or WKPT-0293 Cl.2 cells. Immunostaining of rat kidney cortex or WKPT-0293 Cl.2 cells showed that DMT1 protein was expressed intracellularly and was not present in the plasma membrane. Expression of DMT1 partially colocalized with the late endosomal/lysosomal proteins LAMP1 and cathepsin-L. Using immunogold labeling, DMT1 was shown to be expressed in the membranes of late endosomes/lysosomes. Uptake of Alexa Fluor 546-transferrin was only observed following application to the apical membrane of WKPT-0293 Cl.2 cells. Within these cells, Alexa Fluor 546-transferrin colocalized with DMT1. In conclusion, renal proximal tubular cells express DMT1 in the membranes of organelles, including late endosomes/lysosomes, associated with processing of apically sequestered transferrin. These findings have implications for renal iron handling and possibly for the handling of nephrotoxic metals that are also DMT1 ligands, including Cd2+.

Alternative Splicing↗
PubMed2003

LRIG1 and epidermal growth factor receptor in renal cell carcinoma: a quantitative RT--PCR and immunohistochemical analysis.

In all, 31 renal cell carcinomas (RCCs) were examined for expression of the potential tumour suppressor LRIG1 (formerly Lig-1) and the epidermal growth factor receptor (EGFR). Eight matched samples of uninvolved kidney cortex were also evaluated. Gene expression was examined by quantitative real-time RT-PCR. In the eight matched sample pairs (uninvolved kidney cortex and tumour), protein expression was examined by immunohistochemistry. Conventional (clear cell) tumours showed an expected upregulation of EGFR. LRIG1 expression was generally downregulated in conventional and papillary RCC but not in chromophobic RCC. The ratio between EGFR and LRIG1 was more than 2.5-fold higher in the eight tumours compared with matched uninvolved kidney cortex and was at least two-fold higher than the mean normal ratio in 21 of 31 samples analysed. The observed downregulation of LRIG1 and increased EGFR/LRIG1 ratios are consistent with LRIG1 being a suppressor of oncogenesis in RCC by counteracting the tumour-promoting properties of EGFR. Further studies are justified to elucidate the explicit role of LRIG1 in the oncogenesis of RCC.

Adult↗
PubMed1989

L-pipecolic acid oxidation in the rabbit and cynomolgus monkey. Evidence for differing organellar locations and cofactor requirements in each species.

L-Pipecolic acid oxidation was studied in the rabbit and cynomolgus monkey. Tissue homogenates from both species incubated with L-[2,3,4,5,6-3H]pipecolic acid produced a single radioactive product identified as alpha-aminoadipic acid. In the rabbit, L-pipecolic acid oxidation was greatest in kidney cortex with progressively lesser specific activities in liver, heart, and brain. When rabbit kidney cortex was fractionated by differential centrifugation or on Percoll gradients, activity paralleled that of the mitochondrial marker, glutamate dehydrogenase. In sonicated mitochondria, 92% of the activity was in the soluble fraction. Activity was inhibited by both rotenone and antimycin A and was maximal when FAD, phenazine ethosulfate, and glycerol were included in the assay; Km,app was 0.74 +/- 0.16 mM. Nipecotic acid, piperidine, and cis-2,4-piperidine dicarboxylic acid did not inhibit L-pipecolic acid oxidation, while L-proline had a Ki greater than or equal to 10 mM. D-Alanine and kojic acid, substrate and inhibitor of D-amino acid oxidase, respectively, were also not inhibitory. When monkey kidney cortex was fractionated on Percoll gradients, L-pipecolic acid oxidation activity paralleled that of the peroxisomal marker, catalase. After organellar subfractionation, the activity was membrane-associated and maximal at pH 8.5; Km,app was 4.22 +/- 0.30 mM. L-Pipecolic acid oxidation produced hydrogen peroxide, suggesting involvement of an oxidase in alpha-aminoadipic acid formation. Antimycin A did not inhibit the reaction. No specific cofactor requirements were identified and phenazine ethosulfate inhibited the reaction. D-Pipecolic acid, L-proline, and the other compounds cited above did not significantly inhibit the activity.

Animals↗
PubMedDate not supplied

Asbestos fibers: 1. A modified preparation of tissue samples for analysis by electron microscopy. 2. Presence of fibers in tissues of baboon fed chrysotile asbestos.

A specimen preparation technique is described which yields uniformly dispersed particles on transmission electron microscope (TEM) grids. It is relatively rapid and probably incurs no fiber loss. This technique was used to test the hypothesis that orally administered chrysotile asbestos may pass through the wall of the gastrointestinal tract (GI) of the neonate baboon. A test neonate baboon was bottle-fed chrysotile asbestos which was suspended in a milk formula. Control and test baboons were sacrificed at the end of a 9-day feeding period, and several tissues were removed and preserved. Kidney, liver, and spleen tissues were prepared for TEM analysis. Tissues from the control animal showed no fibers. The number of chrysotile fibers recovered from the test kidney cortex was significantly higher than the level found in the control kidney cortex (p less than 0.005). The frequency distribution of fibers lengths in the kidney cortex was very similar to that of the feeding suspension. This study suggests that a wide range of fiber sizes can penetrate the GI tract and migrate.

Animals↗
PubMed1990

Identification of calcium-calmodulin multifunctional protein kinase II in rabbit kidney.

Recent studies have demonstrated that calcium/calmodulin-dependent multifunctional protein kinase II (CaM-KII) inhibits the reconstituted Na(+)-H+ exchanger from the brush border membrane of proximal convoluted tubule of the rabbit kidney. The present studies were undertaken to evaluate the physiological relevance of this finding by establishing the presence of CaM-KII in rabbit kidney and proximal convoluted tubule cells by Northern RNA hybridization analysis to demonstrate the messenger RNA (mRNA) for CaM-KII and by a selective enzymatic assay of CaM-KII using a synthetic peptide substrate. A single 4.9 Kb mRNA was observed on hybridization of total RNA from rabbit kidney cortex and medulla and from an enriched suspension of rabbit kidney proximal convoluted tubules with a cDNA for rat brain CaM-KII. An enzyme assay using a synthetic peptide substrate representing the site phosphorylated by CaM-KII on glycogen synthase demonstrated calcium-calmodulin dependent protein kinase activity in both rabbit kidney cortex (specific activity of 662 +/- 127 nmol.min-1.mg protein-1) and proximal tubule cells (546 +/- 77 nmol.min-1.mg protein-1). These data establish the presence of CaM-KII in the rabbit kidney, and suggest a role for this enzyme in the control of renal electrolyte transport.

Animals↗
PubMed1995

Relationship between body mass, tissue metabolic rate, and sodium pump activity in mammalian liver and kidney.

The allometric relationship between body mass and tissue metabolism was examined in liver and kidney cortex slices from mouse, rat, rabbit, sheep, and cattle, representing an approximately 12,000-fold difference in body mass and an 11-fold difference in mass-specific basal metabolic rate. Larger mammals have lower tissue metabolic rates (TMR; mumol O2.g wet wt-1.min-1) at 37 degrees C, yielding the equations TMR = 3.6 M-0.21 for liver slices and TMR = 3.2 M-0.11 for kidney cortex slices, where M is body mass in grams. This appears to be an intrinsic property of the tissue and is not due to differences in extracellular space or tissue protein content, because these are relatively constant in all mammalian species examined. The allometric relationships remain when tissue metabolism is expressed relative to "active cell mass" in tissue slices. Potassium uptake rate (KUR; mumol K+.g wet wt-1.min-1) was also measured (as 86Rb+ uptake) and was also lower in larger mammals, yielding the equations KUR = 1.2 M-0.14 in liver slices and KUR = 3.4 M-0.13 for kidney cortex slices. The energetic costs of sodium pump activity were estimated to be < 10% of TMR for liver and kidney cortex from all five mammalian species.

Animals↗
PubMed2004

A blood plasma inhibitor is responsible for circadian changes in rat renal Na,K-ATPase activity.

Rhythmic changes in activity following a circadian schedule have been described for several enzymes. The possibility of circadian changes in Na,K-ATPase activity was studied in homogenates of rat kidney cortex cells. Male Sprague-Dawley rats were kept on a schedule of 12h light (06:00-18:00 h) and 12 h darkness (18:00-06:00 h) for 2 weeks. At the end of the conditioning period, one rat was killed every 2 h, until completion of a 24 h cycle. Outermost kidney cortex slices were prepared, homogenized and assayed for Na,K-ATPase activity. The whole procedure was repeated six times. Na,K-ATPase activity shows an important oscillation (2 cycles/24 h). Peak activities were detected at 09:00 and 21:00 h, whereas the lowest activities were detected at 15:00 and 01:00-03:00 h. The highest activity was 40+/-3 nmoles Pi mg protein(-1)min(-1) (09:00 h), and the lowest was 79+/-3 nmoles Pi mg protein(-1)min(-1) (15:00 h). The amount of the Na+-stimulated phosphorylated intermediate is the same for the 09:00 h and 15:00 h homogenates. Preincubation of 09:00 h kidney cortex homogenates with blood plasma drawn from rats at either 03:00 h or 15:00 h, significantly inhibited their Na,K-ATPase activity. This inhibition was not seen when the preincubation was carried out with either 09:00 h or 21:00 h blood plasma. The striking oscillation (2 cycles/24 h) of the Na,K-ATPase activity of rat kidney cortex cells is ascribed to the presence of an endogenous inhibitor in blood plasma.

Animals↗
PubMed1999

The kidney during hibernation and arousal from hibernation. A natural model of organ preservation during cold ischaemia and reperfusion.

BACKGROUND: During hibernation the kidney is in a hypothermic condition where renal blood flow is minimal and urine production is much reduced. Periodical arousal from hibernation is associated with kidney reperfusion at increasing body temperature, and restored urine production rate. METHODS: To assess the degree of structural preservation during such extreme conditions, the kidney cortex was investigated by means of electron microscopy in the dormouse Muscardinus avellanarius during winter hibernation, arousal from hibernation and the summer active period. RESULTS: Results show that the fine structure of the kidney cortex is well preserved during hibernation. In the renal corpuscle, a sign of slight lesion was the focal presence of oedematous endothelial cells and/or podocytes. Proximal convoluted tubule cells showed fully preserved ultrastructure and polarity, and hypertrophic apical endocytic apparatus. Structural changes were associated with increased plasma electrolytes, creatinine and urea nitrogen, and proteinuria. During the process of arousal the fine structure of the kidney cortex was also well maintained. CONCLUSION: These results demonstrate that dormice are able to fully preserve kidney cortex structure under extreme conditions resembling e.g. severe ischaemia or hypothermic organ storage for transplantation, and reperfusion. Elucidation of the mechanisms involved in such a natural model of organ preservation could be relevant to human medicine.

Animals↗
PubMed1975

Phosphomonoesterase hydrolysis of polyphosphoinositides in rat kidney: Properties and subcellular localization of the enzyme system.

Tthe properties of diphosphoinositide and triphosphoinositide phosphatases from rat kidney homogenate were studied in an assay system in which non-specific phosphatase activity was eliminated. The enzymes were not completely metal-ion dependent and were activated by Mg2+. The detergent sodium deoxycholate, Triton X-100 and Cutscum inhibited the reaction; cetyltrimethylammonium bromide only activated when added with the subtrates and in the presence Mg2+. Both enzymes had a pH optimum of 7.5. Ca2+ and Li+ both activated triphosphoinositide phosphatase, but Ca2+ inhibited and L+ had little effect on diphosphoinositide phosphatase. Cyclic AMP had no effect on either enzyme. The enzymes were three times more active in kidney cortex than in the medulla. On subcellular fractionation of kidney-cortex homogenates by differential and density-gradient centrifugation, the distribution of the enzymes resembled that of thiamin pyrophosphatase (assayed in the absence of ATP), suggesting localization in the Golgi complex. However, the distribution differed from that of the liver Golgimarker galactosyltransferase. Activities of both diphosphoinositide and triphosphoinositide phosphatases and thiamin pyrophosphatase were low in purified brush-border fragments. Further experiments indicate that at least part of the phosphatase activity is soluble.

Animals↗
PubMed1984

Studies on kidney sialidase in normal and diabetic rats.

Rat kidney cortex sialidase was studied using alpha-sialyl-(2----3)-[3H]lactitol and alpha-sialyl-(2----6)-[3H]lactitol as substrates. The enzyme was found mainly in the lysosomal fraction. Only 23% of the sialidase activity of this fraction could be solubilized by a combination of freezing-thawing, sonication and Triton X-100 treatment. The optimal pH for the lysosomal enzyme activity was 4.2 and the enzyme's Km values for alpha-sialyl-(2----3)-lactitol and alpha-sialyl-(2----6)-lactitol were 0.28 and 0.41 mM, respectively. The specific activity was twice as high with the former substrate than with the latter. Sialidase activities in dialyzed kidney cortex homogenates of streptozotocin-diabetic rats and of age-matched control rats were compared. The specific activity was found to be significantly increased in the diabetic animals when using both substrates 5950 +/- 720 (S.E.) dpm/h per mg protein (n = 7) vs. 3970 +/- 370 in the controls (n = 8) with alpha-sialyl-(2----3)-lactitol (P less than 0.025) and 2870 +/- 300 vs. 1820 +/- 170 with alpha-sialyl-(2----6)-lactitol (P less than 0.02). The activities were also found to be increased when expressed per whole kidney cortex (P less than 0.005 and P less than 0.001, respectively). The elevated sialidase activity in diabetic kidney cortex may be related to the reported decrease in sialic acid content of the glomerular basement membrane, which lowers its negative charges and which may contribute to an increased permeability to proteins.

Animals↗
PubMed1983

Increased renal DNA synthesis in vivo after administration of low doses of gentamicin to rats.

Kidney cortex DNA synthesis was studied in female rats treated with a low dose of gentamicin (10 mg/kg) up to 14 days. Synthesis was measured by incorporation of [3H]thymidine into DNA 1 h after intraperitoneal injection of the labeled precursor (200 muCi per animal). Gentamicin given in one injection per day resulted in a greater incorporation of [3H]thymidine into DNA after both 7 and 14 days of treatment as compared with control animals. When the daily dose was divided into three equal injections given at 8-h intervals, a statistically significant increase in thymidine incorporation was observed as early as 4 days after starting gentamicin administration. Excellent agreement was found between DNA specific radioactivity and kidney cortex nuclear labeling, as measured by histoautoradiography. The greatest amount of [3H]thymidine incorporation occurred within proximal tubular cells and interstitial cells. We conclude that a finite duration of gentamicin treatment at low dosage induces an increased DNA synthesis in vivo in rat kidney cortex. We suggest that this reaction results from cellular proliferation and could reflect a regenerative process after focal necrosis induced by gentamicin at low doses. The demonstrated early increase in DNA synthesis could be a useful tool to measure kidney cortex alterations caused by various aminoglycosides at low, therapeutic doses.

Animals↗
PubMed1997

Salt loading enhances rat renal TxA2/PGH2 receptor expression and TGF response to U-46,619.

The tubuloglomerular feedback (TGF) response is potentiated by thromboxane A2 (TxA2) and/or prostaglandin endoperoxide (PGH2) acting on specific receptors. Infusion of the TxA2/PGH2 mimetic, U-46,619, into conscious rats leads to hypertension that is potentiated by a high-salt intake. Therefore, we tested the hypothesis that a high-salt intake enhances the expression of transcripts for TxA2/PGH2 receptors in the kidney and glomeruli and enhances the response of TGF to TxA2/PGH2 receptor stimulation. Groups of rats were accommodated to a low-salt (LS), normal salt (NS), or high-salt (HS) diet for 8-10 days. TxA2/PGH2 receptor mRNA was detected by reverse transcription-polymerase chain reaction in kidney cortex, isolated glomeruli, and abdominal aorta. TxA2/PGH2 mRNA abundance was significantly (P < 0.001) increased during intake of high-salt compared with low-salt diets in the kidney cortex (1.34 +/- 0.10 vs. 0.84 +/- 0.04 arbitrary units) and isolated outer cortical glomeruli (0.68 +/- 0.04 vs. 0.32 +/- 0.03 arbitrary units), but there was no effect of salt on TxA2/PGH2 receptor mRNA expression in the aorta. Maximal TGF responses were assessed from the increase in proximal stop flow pressure (an index of glomerular capillary pressure) during increases in loop of Henle perfusion with artificial tubular fluid from 0 to 40 nl/min. Compared with vehicle, the enhancement of maximal TGF with U-46,619 (10(-6) M) added to the perfusate was greater in rats adapted to high-salt than normal salt (HS: +9.6 +/- 1.1 vs. NS: +5.1 +/- 0.4 mmHg; P < 0.001) or low-salt (LS: +3.8 +/- 1.3 mmHg; P < 0.001) intakes. Responses to U-46,619 at each level of salt intake were blocked by > 70% by the TxA2/PGH2 receptor antagonist ifetroban. In contrast, enhancement of TGF by peritubular capillary perfusion of arginine vasopressin (AVP; 10(-7) M) was similar in high-salt and low-salt rats (HS: +1.5 +/- 0.6 vs. LS: +1.6 +/- 0.5 mmHg; not significant). We conclude that salt loading increases selectively the abundance of TxA2/PGH2 receptor transcripts in the kidney cortex and glomerulus, relative to the aorta, and enhances selectively TGF responses to TxA2/PGH2 receptor activation but not to AVP.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1976

Inhibition of in vitro concentrative prostaglandin accumulation by prostaglandins, prostaglandin analogues and by some inhibitors of organic anion transport.

1. Incubation of rabbit choroid plexus, anterior uvea (iris-ciliary body complex) or slices of kidney cortex in a medium containing tritium-labelled prostaglandin F(2alpha) ([3H]PGF(2alpha) or E1 ([3H]PGE1) results in a four- to thirteenfold concentrative accumulation of 3H activity. 2. Addition of PGF(2alpha, PGF(1) or PGA(1), any one of five PG analogues or a PG precursor, arachidonic acid, at a concentration of 10(-4) M reduced the active accumulation of [3H]PGs by 47-97%. Octanoic acid, at the same concentration, had only a moderate effect on the choroid plexus and no significant inhibitory effect on [3H]PFG(2alpha) accumulation by anterior uvea or kidney cortex. 3. Inhibition was also obtained with 2 mM iodoacetate (under anaerobic conditions) and with 10(-4) M diploretin phosphate, probenecid, iodipamide, indomethacin or dinitrophenol. Perchlorate (10(-4) M) and iodide (10(-4) or 10(-3) M) had no inhibitory effect while 10(-4) M p-aminohippuric acid had a significant inhibitory effect on the kidney cortex at a concentration of 10(-4) M and on the anterior uvea at 10(-3) M. 4. It is concluded that the apparent carrier mediated PG transport systems of the choroid plexus, anterior uvea and kidney cortex are not related to the iodide transport system, but may represent a subcomponent of the iodipamide transport system of these tissues. 5. These results suggest that the systemic distribution and the rate of renal excretion of PGs could be altered by high concentrations of PGs, pharmacologically less active PG analogues, some inhibitors of organic acid transport, and by some inhibitors of PG synthesis and PG action.

Animals↗
PubMed1997

Na+,K(+)-ATPase expression in maleic-acid-induced Fanconi syndrome in rats.

Na+,K(+)-ATPase activity and its alpha 1 subunit protein and mRNA in kidney cortex were monitored in rats developing Fanconi syndrome after the administration of maleate. Na+,K(+)-ATPase activity was significantly lower than in saline-injected controls, although this was partially mediated by a general, non-specific decrease in the cortex protein content. 2. The low activity of the sodium pump correlated with low abundance of alpha 1 subunit mRNA and protein levels. Hsp60 protein levels were also decreased in kidney cortex from maleate-treated rats. 3. Kidney cortex brush-border membrane vesicles from maleate-treated rats showed a marked decrease in Na(+)-dependent alanine and glucose transport, which was not dependent on the Na(+)-transmembrane gradient itself, a finding which is consistent with a more stable effect at the plasma membrane level. 4. The effect of maleate may be partially non-specific and involve a great variety of proteins, but seems to be restricted to selected tissues because alpha 1 subunit Na+,K(+)-ATPase and hsp60 protein amounts were not significantly modified in livers from rats developing Fanconi syndrome. 5. These results show that maleate administration induces a low activity of selected concentrative transport systems and a decrease in Na+,K(+)-ATPase activity and expression. The combination of both effects may explain the increased excretion of most organic solutes present in rats developing Fanconi syndrome.

Alanine↗
PubMed1977

Morphologic changes during incubation of renal slices.

The progression of ultrastructural changes was studied during various conditions of incubation of rat and mice renal cortex slices. The kidneys were sliced with a Stadie-Riggs microtome and incubated in various media (tris(hydroxymethyl) aminomethane (Tris), Tris-proline, and Hanks), in different oxygenation conditions (O2-CO2, 6 liters per minute; N2, 0.5 liter per minute), at different temperatures (37 degrees C, 23 degrees C.) and different time intervals (0 to 120 minutes). The most conspicious changes appear to involve plasma membranes and mitochondria. Early changes (0 to 30 minutes) are mainly confined to mitochondria cristae and matrix; there is also light swelling of the endoplasmic reticulum. After 30 minutes of incubation, the majority of mitochondria have a condensed form: dense matrix and slight dilation of the cristae. These modifications are more accentuated at 75 minutes and many mitochondria are swollen and contain dense material. The modification of the membrane takes place at 30 minutes by vesiculation and/or a diffuse dilation of brush border and is followed by myelinization. The antiluminal membrane appears less sensitive but the same modification pattern appears after 75 minutes. These changes appear more slowly at 23 degrees C. than at 37 degrees C. Kinetic studies were also carried out confirming findings of various authors; cellular uptake and accumulation of 14C-glycine still take place after 2 hours of incubation. The kidney cortex slicing technique does not seem to be suitable for the study of absorption at the luminal membrane. Furthermore, our observations suggest that the generally accepted ultrastructure of some organelles does not correspond to their appearance in the noramlly functioning state in vivo.

Animals↗