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PubMed2006

Tumor necrosis factor alpha down-regulates the Na+-K+ ATPase and the Na+-K+2Cl- cotransporter in the kidney cortex and medulla.

The effect of TNF-alpha on the renal Na+-K+ pump and the Na+-K+2Cl- cotransporter was investigated in the rat. Animals were injected with the cytokine, and 4h later, a homogenate from the cortical and medullary tissues was prepared and used to assay the activity of the Na+-K+ ATPase and the protein expression of the pump and symporter. TNF-alpha reduced the activity and expression of the pump in both cortex and medulla, and its effect disappeared when animals were pre-treated with indomethacin, suggesting that TNF-alpha acts via PGE2. Higher levels of PGE2 were detected by enzyme immunoassay, in kidney tissues isolated from rats treated with PGE2, thus confirming this hypothesis. The cytokine also down-regulated the Na+-K+2Cl- cotransporter but this effect was not abrogated by indomethacin. PGE2, injected into animals, exerted a dose-dependent effect. Low doses did not have any effect on the two transporters in the cortex while high doses inhibited and down-regulated the pump and up-regulated the cotransporter. In the medulla low doses increased the activity and expression of the pump but down-regulated the cotransporter while high doses exerted an exactly opposite effect on the two transporters. It was concluded that the effect of TNF-alpha on the pump is mediated via PGE2 which is released at relatively high doses. The effect of the cytokine on the cotransporter is, however, independent of PGE2.

Animals↗
PubMed1993

Purification and characterization of a membrane-bound protein carboxyl methyltransferase from rat kidney cortex.

Class II protein carboxyl methyltransferases (EC 2.1.1.77) are known to exist predominantly in a soluble form in all cells studied so far. These enzymes have been purified to homogeneity from the cytosols of many mammalian tissues but not from membranes. We describe here the purification to apparent homogeneity of a membrane-associated protein carboxyl methyltransferase from the brush border membrane of rat kidney. The enzyme was purified by fast protein liquid chromatography on Superdex 75 and Mono-Q and by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis and consists of a single 27,300 polypeptide. The purified enzyme recognizes exogenous substrate proteins such as ovalbumin and gamma-globulins as well as synthetic peptides containing a L-isoaspartyl residue but not a synthetic peptide containing a farnesylated C-terminal cysteine (S-farnesyl-LARYKC). The Km for S-adenosyl-L-methionine with ovalbumin as the substrate is 1.5 microM and the purified enzyme is sensitive to inhibition by S-adenosyl-L-homocysteine (Ki = 0.3 microM). Peptide map obtained after Staphylococcus aureus V8 protease digestion of brush border membrane protein carboxyl methyltransferase showed a fragmentation pattern that was identical to that obtained for a soluble protein carboxyl methyltransferase purified according to the same procedure, indicating a high degree of homology. These results support the notion that class II protein carboxyl methyltransferases are not restricted to a cytosolic localization and show that the membrane-bound form of this enzyme shares many characteristics with known cytosolic protein carboxyl methyltransferases.

Amino Acid Sequence↗
PubMed1981

[Demonstration of 2 distinct glomerular populations by a sieving technic in the kidney cortex of the pig].

Amelioration of sieving technics for glomeruli isolation aims at obtention of purer and more homogeneous preparations, presenting a high preservation degree for glomerular functional studies. We have recently demonstrated the necessity to use sieves adapted to the glomeruli size of different considered animals as well as to use kidneys having exactly the same weight in order to obtain very homogeneous glomeruli suspensions. This study presents a new amelioration in the homogeneity of the glomeruli diameter through a preliminary dissection of the renal cortex in order to isolate glomeruli situated in the same particular cortical zone. Pig renal cortex, because of its size, agrees well with a fine dissection in order to dissociate the superficial and the juxta-medullary zones. Glomeruli are isolated with 160/120 micro mesh sieves. Diameter mean value is 218.8 +/- 30.1 micro in superficial glomeruli and 270.4 +/- 30.1 micro in juxta-medullary ones, highly significant difference, (p less than 0.001). Moreover, repartition frequency histograms of the juxta-medullary glomerular populations diameter presents a large shifting to higher values. This renal dissection preceding the glomeruli isolation sieving technique contributes to better the homogeneity of the isolated glomeruli suspensions and opens the way to the original study of the comparative in vitro vasoreactivity of these two different glomerular populations after incubation with physiological or pharmacological reagents.

Animals↗
PubMed1997

Regucalcin increases Ca2+-ATPase activity and ATP-dependent calcium uptake in the microsomes of rat kidney cortex.

The effect of regucalcin, a Ca2+-binding protein, on Ca2+ transport system in rat renal cortex microsomes was investigated. The presence of regucalcin (10[-8] to 10[-6] M) in the reaction mixture caused a significant increase in Ca2+-ATPase activity and ATP-dependent 45Ca2+ uptake in the microsomes. Regucalcin (10[-7] M) increased Ca2+-ATPase activity independently of increasing concentrations of CaCl2. The microsomal Ca2+-ATPase activity and 45Ca2+ uptake were markedly decreased by the presence of vanadate (0.1 mM) or N-ethylmaleimide (NEM; 5 mM) in the absence or presence of regucalcin. Dithiothreitol (DTT; 5 mM) markedly elevated Ca2+-ATPase activity and 45Ca2+ uptake in the microsomes. The DTT effects were not further enhanced by regucalcin (10[-7] M). Meanwhile, the microsomal Ca2+-ATPase activity and 45Ca2+ uptake were significantly decreased by the presence of dibutyryl cyclic AMP (DcAMP; 10[-5] and 10[-3] M) or inositol 1,4, 5-trisphosphate (IP3; 10[-7] and 10[-5] M). The effect of regucalcin (10[-7] M) on Ca2+ATPase activity and 45Ca2+ uptake was weakened in the presence of DcAMP or IP3. The present results demonstrate that regucalcin has a stimulatory effect on ATP-dependent Ca2+ uptake in the microsomes of rat renal cortex due to acting on the thiol groups of Ca2+-ATPase.

Adenosine Triphosphate↗