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PubMed1976

A study on the properties of mitochondria from rat kidney cortex and red medulla.

Mitochondria of rat kidney red medulla form a single band (rho = 1.163) on a sucrose gradient, while mitochondria of the cortex form bands in 2 density regions, namely ca. 66% (M1) at rho = 1.173 and ca. 33% (M2) at rho = 1.163. The mitochondria of the red medulla contain more cytochrome a, more cytochrome b, and less cytochrome c, compared to the M1 population which predominates in cortex. Mitochondria from the red medulla show higher rates of Pi incorporation into total organically bound phosphorus in the presence of ADP, Pi, and oxidizable substrate than do mitochondria from cortex. However, in absence of added oxidizable substrate the reverse is observed, indicating that isolated cortex mitochondria contain more endogenous substrate. The superiority of the red medulla organelles in phosphorylation in the presence of substrate persists in preparations made according to LOWENSTEINS [3] procedure (shortened isolation time, removal of lysosomal enzymes by digitonin treatment). This shows that the observed differences are not artifacts due to different degrees of damage to the organelles by lysosomal attack.

Animals↗
PubMed1990

Extracellular matrix receptors in the kidney cortex.

Extracellular matrix (ECM) receptors anchor cells to substratum and impart positional information to cells. Within the group of ECM receptors known as integrins, alpha-subunits of these alpha beta heterodimers define ligand specificity, whereas beta-subunits define the subclass. We used immunofluorescence with anti-ECM receptor antibodies to examine distribution within human kidney cortex of all known alpha-subunits in the beta 1 subclass of integrins as well as a non-integrin 67-kDa elastin/lamin receptor. The alpha 1-subunit (alpha 1 beta 1 defines a collagen receptor) was present in mesangium and base of all tubule epithelial cells; alpha 2 (collagen) was present in mesangium and in distal but not proximal tubule cells; alpha 3 (collagen, laminin, fibronectin) was diffusely distributed within glomeruli but tubule staining was less intense; alpha 4 (fibronectin) was absent; alpha 5 (fibronectin) was present in blood vessels; and alpha 6 (laminin) was present along basolateral aspect of all tubule cells but absent in glomeruli. The elastin/laminin receptor was present in all tubule epithelial cells, but staining was heavier in distal tubules, especially intercalated cells. Thus striking heterogeneity in ECM receptor distribution was noted. For collagen receptors, differences in tubule staining were pronounced. Despite the presence of laminin within both glomeruli and tubules, laminin receptors also showed marked differences in staining between these structures. Both differences in ECM structure and intrinsic differences among different cells may underlie these differences in ECM receptor distribution.

Collagen↗
PubMed1987

Mechanism of transport for toxic cysteine conjugates in rat kidney cortex membrane vesicles.

Cysteine conjugate transport plays a key role in the interorgan transport of xenobitoic metabolites which are formed via the mercapturic acid pathway. In the rat, transport of cysteine conjugates could be an important factor in the selective nephrotoxicity of some toxic cysteine conjugates. However, little information is available on the molecular mechanism(s) of cysteine conjugate transport in the rat kidney. Therefore, we have investigated the polarity and the molecular driving forces for the transport of S-(1,2-dichlorovinyl)-L-cysteine (DCVC) in isolated membrane vesicles from rat kidney cortex. Our data suggest that Na+-dependent transport on the lumenal side is responsible for the uptake of cysteine conjugates across the apical membrane. No Na+-stimulated transport was found on the basolateral side and uptake of DCVC in basolateral membrane vesicles was not saturable. Na+-dependent transport in brush border membrane vesicles was inhibited by a variety of neutral amino acids and cysteine conjugates, but not by polar amino acids. Therefore, the transporter is similar to the Na+-dependent neutral amino acid transporter of rat kidney brush border membranes. The system L-specific substrate, 2-amino-2-norbornane carboxylic acid, was not inhibitory. The Km for the Na+-stimulated transport system in brush border membrane vesicles was 225 microM and the Vmax was 782 pmol/15 sec/mg of protein. We propose that the driving force for the apical transport of cysteine conjugates may be the coupling of the lumenal transport to the Na+-gradient. The data are discussed with regard to a transepithelial transport model for cysteine conjugates and the role transport plays in the molecular mechanism of cysteine conjugate toxicity.

Animals↗
PubMed2000

Localization of epithelial sodium channel and aquaporin-2 in rabbit kidney cortex.

The amiloride-sensitive epithelial sodium channel (ENaC) and the vasopressin-dependent water channel aquaporin-2 (AQP2) mediate mineralocorticoid-regulated sodium- and vasopressin-regulated water reabsorption, respectively. Distributions of ENaC and AQP2 have been shown by immunohistochemistry in rats. Functional data from rabbits suggest a different distribution pattern of these channels than in rats. We studied, by immunohistochemistry in the rabbit kidney cortex, the distributions of ENaC and AQP2, in conjunction with marker proteins for distal segments. In rabbit cortex ENaC is restricted to the connecting tubule (CNT) cells and cortical collecting duct (CCD) cells. The intracellular distribution of ENaC shifts from the apical membrane in the most upstream CNT cells to a cytoplasmic location further downstream in the CNT and in the CCD cells. AQP2 is detected in the CCD cells exclusively. The anatomic subdivisions in the rabbit distal nephron coincide exactly with distributions of apical transport systems. The differences between rabbits and rats in the distribution patterns of ENaC and AQP2 may explain functional differences in renal salt and water handling between these species.

Animals↗
PubMed1985

Isoenzymes of N-acetyl-beta-D-glucosaminidase in kidney cortex and urine of normal and nephritic rats.

Induction of acute Heyman nephritis in rats gave a significant increase in the urinary excretion of protein (p less than 0.001) and N-acetyl-beta-D-glucosaminidase (NAG; p less than 0.01) 14 days after injection of antibody. The isoelectric points (IP) of NAG were studied by chromatofocusing of the urine, serum and various lysosomal populations purified from kidney cortex homogenates of normal and nephritic rats. The chromatofocusing profiles for serum NAG (IP = 5.8) were totally different from the patterns found in normal and nephritic urines. The acidic IPs of NAG in normal urine (IP = 5.0) were changed into slightly more basic values in nephritic urine (IP = 5.15). Similar changes were also demonstrated in normal urine after acidification and prolonged incubation. The chromatofocusing profile obtained for NAG in the large, dense lysosomes was almost identical to the pattern observed in nephritic urine and demonstrated IPs for NAG in a slightly more basic pH area than observed for small and medium-sized lysosomes. The difference in IP in normal and nephritic urines may therefore be due to an increased autolytic degradation of NAG or excretion of the enzyme from different populations of lysosomes.

Acetylglucosaminidase↗
PubMed1990

Inhibition by substrate of fructose 1,6-bisphosphatase purified from rat kidney cortex. Calculation of the kinetic constants of the enzyme.

Fructose 1,6-bisphosphatase is a typical enzyme that is severely inhibited by its own substrate. This makes it difficult to determine all the parameters involved in its kinetics. It has been shown recently that if Vm is satisfactorily estimated the remaining parameters can be determined using the Hill plot (Bounias, M. (1988) Biochem. Int. 17, 147-154). The enzyme has been purified from rat kidney cortex nearly to homogeneity, and its kinetic constants have been calculated using a rigorous algebraic method. The most interesting result is that the substrate is unable to bind to the free enzyme as an inhibitor, which indicates that the enzyme lacks an allosteric site for hexose bisphosphates.

Animals↗
PubMed1988

ATP-driven Ca2+ pump in the basolateral membrane of rat kidney cortex catalyzes an electroneutral Ca2+/H+ antiport.

An ATP-driven Ca2+ pump in the basolateral membrane of rat kidney cortex pumps Ca2+ out of the cell at the expense of MgATP (Km = 0.191 mM). This pump has a high affinity for free Ca2+ (26 nM). Vanadate, lanthanum, N-ethylmaleimide and calmodulin inhibitor R24571 inhibited this pump activity. Dimethyl[2-14C]oxazolidine-2,4-dione [( 14C]DMO) was entrapped in the vesicles in association with the ATP-driven Ca2+ influx. The ATP-driven Ca2+ influx was stimulated by the intravesicular acid pH and an upper convex Lineweaver-Burk reciprocal plot suggested two possible kinetics; one is that this Ca2+ pump is an allosteric enzyme with more than 1.72 H+ binding sites and another is the presence of two Ca2+ pumps with different affinities for H+. Valinomycin study indicated that the ATP-dependent Ca2+ transport by the BLMV was electroneutral and voltage independent. These results strongly suggest that the ATP-driven Ca2+ pump in the renal basolateral membrane catalyzes an electroneutral Ca2+/H+ antiport.

Adenosine Triphosphate↗
PubMed1987

Angiotensin receptor subtypes of the kidney cortex.

Angiotensin II (ANG II) binds with high affinity to specific renal receptors and exerts major influences on hemodynamics and tubular transport. Glomerular and tubular epithelial receptors are well characterized in contrast to pre- and postglomerular and medullary vasculature. Therefore, the scope of this review is limited to an indepth comparison of ANG II receptor kinetics, analogue specificity, and mechanisms of receptor regulation and signal transduction in glomeruli and epithelial cells. Despite the fact that these receptors are in close proximity anatomically, there is evidence from a number of laboratories that permits classification into two distinct receptor subtypes. The receptor of the glomerular mesangium, classified herein as "type A," is characterized by high affinity for ANG II and the heptapeptide, des-Asp1-Ang II (ANG III), "downregulation" with high ambient concentrations of ANG II and signal transduction mediated by phospholipase C-induced Ca2+ transients. The tubular epithelial ANG II receptor, "type B," is of lower affinity for ANG II and ANG III, "upregulated" by high levels of ANG II and mediates inhibition of adenylate cyclase following coupling to an inhibitory GTP binding protein. Both receptors possess secondary mechanisms of signal transduction that may also participate in regulation of cellular function(s). These findings support the hypothesis that at least two distinct classes of ANG II receptors are present in the kidney cortex.

Angiotensin II↗
PubMed1998

In vivo measurement of T1 and T2 relaxivity in the kidney cortex of the pig--based on a two-compartment steady-state model.

A two-compartment system for approximating five successive steady-state levels of gadopentetate dimeglumine (Gd-DTPA) concentration in pigs was developed. The method of calculating Gd-DTPA concentration was based on a simultaneous reference determination of 99mTc-DTPA. Experimental and theoretical results showed a steady state after 25 min. The nuclear magnetic resonance (NMR) relaxivities of Gd-DTPA were determined in vivo in pig kidneys during steady-state levels. T1 relaxivity (R1) and T2 relaxivity (R2) in the kidney cortex were found to be 1.1+/-0.03 and 2.0+/-0.2 (s(-1) mM(-1)), respectively. R1 and R2, in in vitro human plasma solutions at 25 degrees C were 5.3+/-0.02 and 5.8+/-0.06 s-1 mM-1 and at 37 degrees C 4.3+/-0.04 and 4.9+/-0.01 s(-1) mM(-1). Thus, the in vivo relaxivities were reduced 3.9 and 2.5 times for R1 and R2, respectively, compared to the in vitro relaxivities. This marked difference in relaxivities between tissue and plasma may be the result of the difference in steric relations. In plasma, the mobility and distribution of the Gd-DTPA complex are unrestricted, whereas they may be reduced in the tissues because of the close proximity to the cell wall, to the proteins and to other extracellular elements and compartments.

Animals↗
PubMed1996

Expression cloning and functional characterization of the kidney cortex high-affinity proton-coupled peptide transporter.

The presence of a proton-coupled electrogenic high-affinity peptide transporter in the apical membrane of tubular cells has been demonstrated by microperfusion studies and by use of brush border membrane vesicles. The transporter mediates tubular uptake of filtered di- and tripeptides and aminocephalosporin antibiotics. We have used expression cloning in Xenopus laevis oocytes for identification and characterization of the renal high-affinity peptide transporter. Injection of poly(A)+ RNA isolated from rabbit kidney cortex into oocytes resulted in expression of a pH-dependent transport activity for the aminocephalosporin antibiotic cefadroxil. After size fractionation of poly(A)+ RNA the transport activity was identified in the 3.0- to 5.0-kb fractions, which were used for construction of a cDNA library. The library was screened for expression of cefadroxil transport after injection of complementary RNA synthesized in vitro from different pools of clones. A single clone (rPepT2) was isolated that stimulated cefadroxil uptake into oocytes approximately 70-fold at a pH of 6.0. Kinetic analysis of cefadroxil uptake expressed by the transporter's complementary RNA showed a single saturable high-affinity transport system shared by dipeptides, tripeptides, and selected amino-beta-lactam antibiotics. Electrophysiological studies established that the transport activity is electrogenic and affected by membrane potential. Sequencing of the cDNA predicts a protein of 729 amino acids with 12 membrane-spanning domains. Although there is a significant amino acid sequence identity (47%) to the recently cloned peptide transporters from rabbit and human small intestine, the renal transporter shows distinct structural and functional differences.

Amino Acid Sequence↗
PubMed2002

Purinergic regulation of glucose and glutamine synthesis in isolated rabbit kidney-cortex tubules.

The effects of extracellular purinergic agonists and their breakdown products on glucose and glutamine synthesis in rabbit kidney-cortex tubules incubated with aspartate + glycerol or alanine + glycerol + octanoate were investigated. A rapid extracellular degradation of ATP was accompanied by an accumulation of AMP, inosine, and hypoxanthine. Extracellular ATP and its breakdown products accelerated glucose synthesis in renal tubules, while ammonium released from adenine-containing compounds enhanced glutamine synthesis and diminished the degree of gluconeogenesis stimulation. In contrast to AMP and inosine, ATP evoked calcium signals, while both ATP and inosine decreased intracellular cAMP content and accelerated the flux through fructose-1,6-bisphosphatase as concluded from changes in gluconeogenic intermediates. Since (i) the activity of partially purified renal fructose-1,6-bisphosphatase was increased upon protein phosphatase-1 treatment and decreased following treatment of previously dephosphorylated enzyme with protein kinase A catalytic subunit and (ii) both 8-bromoadenosine 3',5'-cyclic monophosphate and 8-(4-chlorophenyltio)-cAMP inhibited renal glucose synthesis, it seems likely that in rabbit renal tubules ATP and inosine stimulate gluconeogenesis via cAMP decrease, which favors the appearance of a more active, dephosphorylated form of fructose-1,6-bisphosphatase, a key gluconeogenic enzyme.

Adenosine↗
PubMed1985

Age-related change in brush borders of rat kidney cortex.

Age-related change of rat renal brush borders was examined with electron microscopy and biochemical procedures. Total activity of renal brush border enzymes, such as alkaline phosphatase and leucine aminopeptidase in the homogenate, was significantly decreased with age. Acid phosphatase activity and protein content were not significantly changed with age. Specific activity of leucine aminopeptidase in brush border fraction was significantly decreased at a later stage of age. Protein content of brush border fraction was decreased significantly with age. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, some of the proteins disappeared during aging. Electron microscopic observations of kidney cortex showed that microvilli of renal brush borders from old rats were observed to be fewer than those from the young; epithelial cells in young rats have more densely packed brush border projections than those in old rats. From these results, it is suggested that during aging renal brush borders are degraded, and that protein components of the brush borders were different between old and young.

Acid Phosphatase↗
PubMed1994

Expression of taurine transporter and its regulation by diet in Xenopus laevis oocytes following injection of rat kidney cortex mRNA.

NaCl-dependent taurine transport adapts to changes in the dietary intake of sulfur amino acids. The renal adaptive response is expressed by enhanced NaCl-dependent taurine cotransport by brush border membrane vesicles after a low taurine diet and reduced transport after a high taurine diet as compared to a normal taurine diet. In order to determine if this adaptive regulation is dependent on new protein synthesis, the Xenopus laevis oocyte expression system was utilized to define the translational regulation of taurine transporter activity. Poly(A)+ RNA was isolated from kidney cortex of Sprague Dawley rats fed either a low, normal or high taurine diet for 28 days. Injection of poly(A)+ RNA resulted in a time- and dose-dependent increase in NaCl-taurine co-transport. Taurine uptake was stimulated about 2-10-fold after injection of poly(A)+ RNA (10-40 ng) as compared to H2O-injected oocytes. Taurine uptake by oocytes was sodium- and anion-dependent (Cl- > Br- > SCN- > I-). The Km and Vmax of the taurine transporter were 22.5 microM and 8.35 pmol/h/oocyte respectively, similar to the Km of 17.0 microM found in rat brush border membrane vesicles. Because the adaptive response involves an augmented or reduced Vmax of the transporter, taurine uptake by oocytes injected with poly(A)+ RNA from rats fed each diet was examined. Poly(A)+ RNA from rats fed a low taurine diet elicited twice the taurine uptake elicited from rats fed a normal taurine diet and more than three times the uptake from high taurine-fed rats. Northern blot analysis after hybridization with an RNA probe for the taurine transporter cDNA from MDCK cells (obtained from Dr. Uchida) indicated that the molecular size of taurine transporter mRNA is about 1.9 kb and is regulated by diet. Expression of taurine transporter by the oocytes injected with 30 ng of capped transcript from pNCT was significantly reduced by taurine in the medium. In conclusion, taurine uptake by oocytes after injection of mRNA is similar to brush border membrane vesicles taurine transport. The long-term adaptive response is regulated at the level of mRNA, and the short-term adaptive response is regulated at the level of protein synthesis or secretion. We speculate that the renal adaptive response to altered dietary sulfur amino acid intake is both transcriptionally and translationally regulated.

Animals↗
PubMed1983

Beta-adrenergic stimulation of Ca2+ fluxes, endocytosis, hexose transport, and amino acid transport in mouse kidney cortex is mediated by polyamine synthesis.

We recently found that the beta-adrenergic agonist 1-isoproterenol evokes a rapid (less than 5 min) Ca2+- and receptor-dependent stimulation of endocytosis, hexose transport, and amino acid transport in mouse renal cortex involving proximal tubule cells. This response is associated with increased Ca2+ fluxes and a mobilization of mitochondrial calcium, suggesting that stimulus-response (stimulus-"transport") coupling is mediated by cytosolic Ca2+. We show here that 1 microM isoproterenol evokes a rapid (less than 60 sec) transient increase in the activity of ornithine decarboxylase followed by an early (less than 2 min) sustained increase in putrescine, spermidine, and spermine concentrations in mouse kidney cortex slices in vitro. Small doses of isoproterenol (down to 24 nmol/kg) elicited a rapid (less than 2 min) increase in polyamines in vivo. The ornithine decarboxylase inhibitor alpha-difluoromethylornithine (5 mM) suppressed the testosterone-induced increase in polyamine levels and rates of endocytosis, hexose transport, and amino acid transport, measured by horseradish peroxidase, [14C]aminoisobutyric acid, and deoxy[3H]glucose uptake. alpha-Difluoromethylornithine also blocked the isoproterenol-induced increase in 45Ca influx and efflux and 45Ca redistribution; 0.5 mM putrescine nullified alpha-difluoromethylornithine inhibition and restored the increment in polyamines, 45Ca fluxes, endocytosis, hexose transport, and amino acid transport. These data implicate polyamine synthesis in isoproterenol stimulation of Ca2+ fluxes and membrane transport processes and support a model for signal transduction and stimulus-response coupling in which ornithine decarboxylase activation and polyamine synthesis play a pivotal role in regulating Ca2+ fluxes. In this model the polyamines generate local Ca2+ signals by stimulating Ca2+ influx or mobilizing intracellular calcium (or both) through a cation exchange reaction.

Amino Acids↗
PubMed1979

Sulphate-ion/sodium-ion co-transport by brush-border membrane vesicles isolated from rat kidney cortex.

Uptake of SO(4) (2-) into brush-border membrane vesicles isolated from rat kindey cortex by a Ca(2+)-precipitation method was investigated by using a rapid-filtration technique. Uptake of SO(4) (2-) by the vesicles was osmotically sensitive and represented transport into an intra-vesicular space. Transport of SO(4) (2-) by brush-border membranes was stimulated in the presence of Na(+), compared with the presence of K(+) or other univalent cations. A typical ;overshoot' phenomenon was observed in the presence of an NaCl gradient (100mm-Na(+) outside/zero mm-Na(+) inside). Radioactive-SO(4) (2-) exchange was faster in the presence of Na(+) than in the presence of K(+). Addition of gramicidin-D, an ionophore for univalent cations, decreased the Na(+)-gradient-driven SO(4) (2-) uptake. SO(4) (2-) uptake was only saturable in the presence of Na(+). Counter-transport of Na(+)-dependent SO(4) (2-) transport was shown with MoO(4) (2-) and S(2)O(3) (2-), but not with PO(4) (2-). Changing the electrical potential difference across the vesicle membrane by establishing different diffusion potentials (anion replacement; K(+) gradient+/-valinomycin) was not able to alter Na(+)-dependent SO(4) (2-) uptake. The experiments indicate the presence of an electroneutral Na(+)/SO(4) (2-)-co-transport system in brush-border membrane vesicles isolated from rat kidney cortex.

Animals↗