Kidney Cortex Brush-border Membrane Research Articles

Intestinal and Renal Adaptations to Changes of Dietary Phosphate Concentrations in Rat.

We have studied the role of the intestine, kidney, and several hormones when adapting to changes in dietary P concentration. Normal and parathyroidectomized (PTX) rats were fed pH-matched diets containing 0.1%, 0.6%, and 1.2% P concentrations. 32Pi uptake was determined in the jejunum and kidney cortex brush border membrane vesicles. Several hormone and ion concentrations were determined in the blood and urine of rats. Both jejunum and kidney cortex Pi transport was regulated with 5 d of chronic feeding of P diets in normal rats. Acute adaptation was determined by switching foods on day 6, which was only clearly observed in the kidney cortex of normal rats, with more statistical variability in the jejunum. However, no paradoxical increase of Pi uptake in the jejunum was reproduced after the acute switch to the 1.2% P diet. Pi uptake in the jejunum was parathyroid hormone (PTH)-independent, but in the kidney, the chronic adaptation was reduced, and no acute dietary adaptations were observed. The NaPi2a protein was more abundant in the PTX than the sham kidneys, but contrary to the modest or absent changes in Pi uptake adaptation, the transporter was similarly regulated by dietary P, as in the sham rats. PTH and fibroblast growth factor 23 (FGF23) were the only hormones regulated by all diet changes, even in fasting animals, which exhibited regulated Pi transport despite similar phosphatemia. Evidence of Pi appetite effects was also observed. In brief, our results show new characteristics of Pi adaptations, including a lack of correlation between Pi transport, NaPi2a expression, and PTH/FGF23 concentrations.

Intestinal and Renal Pi Transport Adaptation and Hormonal Changes in Response to Acute Changes in Dietary Pi

A hallmark of the successful control of Pi homeostasis is the adaptation of Pi intestinal absorption and renal excretion to changes in the dietary content of Pi. Acute and chronic adaptation mechanisms have been described for both tissues, yet despite these efforts, many questions related to hormonal changes and transport systems are still unclear. Male Wistar rats were fed well-balanced fodder containing either 0.1, 0.6, or 1.2% Pi, prepared with NaH2PO4 and K2HPO4 to pH 7.4 and compensated with NaCl and KCl. Some rats were fed ad libitum for 6 days, while other animals were fed only 4 hours in the morning for 6 days. Some of the rats from this 4-hour feeding scheme that had been fed either 0.1 or 1.2% Pi fodder for 5 days received the opposite fodder on the 6th day. Food consumption, Pi ingestion, and growth were determined. Pi deficiency-related acidosis was minimally observed in the animals that, after 5 days eating 1.2% Pi food, were switched to 0.1% Pi on the 6thday: blood pH was reduced to 7.32, bicarbonate fell to 25.2 mM, and the base excess dropped to -1.74 mM. Pi transport in jejunum and kidney cortex brush border membrane vesicles (BBMV) was always higher in the animals chronically fed with 0.1% Pi, and it was similar at 0.6 and 1.2% Pi. In the case of animals whose diet was switched the last day, there were no differences in jejunum BBMV Pi transport, in contrast to previous studies that have shown a higher transport rate after switching to a high Pi content. In kidney BBMV, Pi transport was higher in the change from 1.2 to 0.1% Pi. Plasma Pi was always proportional to the fodder Pi content. Plasma FGF23 and PTH concentrations varied similarly and were always proportional to the ingested Pi in all groups, including the animals whose food was switched, meaning that both hormones changed after 4 hours of high Pi intake. Differences in the phosphatonins sFR4 and MEPE were not significant. Also, no differences were observed in dopamine, corticosterone, insulin, thyroxine, calcitriol, or Klotho. A similar experiment was performed in parathyroidectomized (PTX) rats, but only using the 4-hour feeding regime. Food consumption and growth was similar in sham and PTX animals. Blood plasma Pi was higher in PTX animals in all groups except for those chronically fed at 0.1% Pi. Transport in jejunum BBMV was similar in sham and PTX rats, and NaPi2b protein abundance correlated with the transport rate. In kidney BBMV, all groups showed higher transport rates in PTX rats (except for the chronic 0.1% Pi group, in which the rates were similar), and no differences were observed between the animals whose food was acutely switched the last day, therefore confirming the role of PTH over the relevance of FGF23 in the kidney's acute response. All hormones behaved similarly in sham and PTX animals, except for dopamine, which was very low in the 0.1%-Pi fed PTX rats, and FGF23 which was surprisingly lower in all groups compared to sham rats. In conclusion, a pH- and ion-balanced fodder prevented the paradoxical increase of Pi intestinal uptake when a Pi-enriched food was given. This food also prevented the strong metabolic acidosis associated with experimentally Pi-depleted fodder. Acute adaptation only occurs in the kidney, and PTH is the hormone that mediates it.

The calcium-activated chloride channel Anoctamin 1 contributes to the regulation of renal function

The role of calcium-activated chloride channels for renal function is unknown. By immunohistochemistry we demonstrate dominant expression of the recently identified calcium-activated chloride channels, Anoctamin 1 (Ano1, TMEM16A) in human and mouse proximal tubular epithelial (PTE) cells, with some expression in podocytes and other tubular segments. Ano1-null mice had proteinuria and numerous large reabsorption vesicles in PTE cells. Selective knockout of Ano1 in podocytes (Ano1-/-/Nphs2-Cre) did not impair renal function, whereas tubular knockout in Ano1-/-/Ksp-Cre mice increased urine protein excretion and decreased urine electrolyte concentrations. Purinergic stimulation activated calcium-dependent chloride currents in isolated proximal tubule epithelial cells from wild-type but not from Ano1-/-/Ksp-Cre mice. Ano1 currents were activated by acidic pH, suggesting parallel stimulation of Ano1 chloride secretion with activation of the proton-ATPase. Lack of calcium-dependent chloride secretion in cells from Ano1-/-/Ksp-Cre mice was paralleled by attenuated proton secretion and reduced endosomal acidification, which compromised proximal tubular albumin uptake. Tubular knockout of Ano1 enhanced serum renin and aldosterone concentrations, probably leading to enhanced compensatory distal tubular reabsorption, thus maintaining normal blood pressure levels. Thus, Ano1 has a role in proximal tubular proton secretion and protein reabsorption. The results correspond to regulation of the proton-ATPase by the Ano1-homolog Ist2 in yeast.

Abstract 626: Caveolin-1 (CAV1) Levels Determine the Cell Surface Expression of the Dopamine D1-like Receptors

In human renal proximal tubule cells, the dopamine-1 receptor (D1R) increases cAMP production and negatively regulates sodium transport. Defects in D1R signaling have been associated with SNPs in G-protein coupled receptor kinase type 4 (GRK4), which hyperphosphorylates and decreases D1R function, leading to sodium retention. We have previously shown that knockdown of CAV1 in proximal tubule cells impairs sodium transport. In this report we show that CAV1 reduction, knockdown or knockout leads to decreased dopamine D1-like receptor binding at the proximal tubule cell surface. Dopamine D1-like brush border and cell surface binding was measured using Bodipy-FL conjugated SKF83566 . WT and Caveolin 1 knockout (CAV1KO) kidney cortex brush border membrane isolation was performed by magnetic lotus tetragonolobus agglutinin affinity purification and fluorescent SKF83566 binding by microplate fluorometry. CAV1KO had a 35.8±3.3% decrease in binding vs WT (p<0.01, n=6 per group, WT level 18,492 RFU above background). In hTERT immortalized human renal proximal tubule cell lines, lentiviral shRNAi CAV1 stable knockdown cell lines had a 76.4±2.5%, p<0.001 n=4, reduction in CAV1 expression by western blot. Cell surface D1-like receptor binding was reduced by 34.0±1.3% (p<0.001, n=4) in the CAV1 knockdown cell lines (scrambled control levels 117193 RFU). We previously have shown that CAV1 expression is dramatically reduced in the hypertensive SHR proximal tubule cell line vs the normotensive WKY proximal tubule cell line. The SHR cell line had a 57.5±1.2% (p<0.001, n=7) reduction in D1-like receptor binding (WKY 116114 RFU). Re-expression of rat CAV1 alpha or CAV1 beta isoform in the SHR cell line by stable lentiviral infection increased binding by 51.6±2.1%, and 63.3±1.6% respectively (p<0.01, n=14). Sodium transport was decreased by CAV1 alpha and CAV1 beta expression in SHR cell lines. The average number of domes per 10x objective fields of view was 9.5±1.6 in SHR cell, 4.5±0.3 in SHR CAV1alpha (p<0.05, n=4 vs SHR) and in SHR CAV1beta 5.0±0.3 (p<0.05, n=4 vs SHR). In mouse, rat, and human renal proximal tubule cells, CAV1 is necessary for dopamine D1-like receptor cell surface localization and for normal dopaminergic inhibition of sodium transport.

Role of rat sodium/phosphate cotransporters in the cell membrane transport of arsenate

Inorganic arsenate (As V) is a common contaminant of underground water. Following oral exposure, it is assumed that As V is distributed and crosses cell membranes through inorganic phosphate (Pi) transporters. We have tested this hypothesis by studying the inhibition of rat Na/Pi cotransporters by As V in Xenopus laevis oocytes and in several rat tissues. The ubiquitously expressed type III Pi transporters (PiT-1 and PiT-2) showed a low affinity for As V ( K i ~ 3.8 mM), similar to the Pi transport system in aortic vascular smooth muscle cells ( K i 1.5 mM). The type II renal isoforms, NaPi-IIa and NaPi-IIc, were also poorly inhibited by As V ( K i ~ 1 mM), similar to the Pi transport from kidney cortex brush-border membrane (BBM) vesicles. Conversely, the high-affinity intestinal transporter, NaPi-IIb, was very efficiently inhibited with a K i of 51 μM, similar to the Pi transport from intestinal BBM vesicles. Taking into account the 1.1 mM Pi in blood and renal ultrafiltrate, and the nanomolar range of As V exposures, we have determined that the contribution by Na/Pi cotransporters to As V membrane transport is negligible, given that 10–15 mM As V would be necessary in these fluids to be significantly transported. Intestinal transport is an exception, because Pi competition is weak, thereby considering that its concentration in lumen mainly depends on low Pi levels from ingested fresh water, and because As V very efficiently inhibits Pi intestinal transport. Our data agree with current toxicokinetic knowledge, and they explain the asymmetric excretion of trivalent and pentavalent arsenic species into bile and urine.

Thermotropic Lipid Phase Transition and the Behavior of Hydrolytic Enzymes in the Kidney Cortex Brush Border Membrane

Functional interactions of lipids and proteins were examined in brush-border membranes isolated from the kidney cortex by studying the temperature dependence of the hydrolytic enzyme activities. A close relationship was observed for the membrane proteins and the thermotropic lipid phase transitions. Three lines of evidences were provided for such dependence: a) Arrhenius relationship of the membrane-bound enzyme activities, and the effect of temperature in native and partially delipidated membranes, b) differential scanning calorimetric study of the membrane lipid phase transitions in the native and delipidated membranes, multilamellar vesicles prepared from the membrane extracted lipids, and in vesicles from dimyristoyl phosphatidylcholine, and c) the excimer (dimer)-formation studies of the membrane extrinsic fluorescent probe, pyrene, and the resultant membrane microviscosity. The brush-border membranes were partially delipidated with BuOH and 2,2,2-trifluoroethanol. The functional interactions of the delipidated membranes, which were greatly lost on lipid removal, were largely restored by the addition of exogenous lipids in the reconstitution process, which indicate the critical dependence of the membrane integral proteins on the neighboring lipid molecules in the bulk lipid phase.

The intrinsic Cl- conductance of mouse kidney cortex brush-border membrane vesicles is not related to CFTR.

Brush-border membrane vesicles (BBMV) were prepared from whole Balb/c mice kidneys by a Mg2+ precipitation technique. The presence of an intrinsic Cl- conductance co-expressed with Na+/glucose cotransport was inferred by the anion dependence of [14C]glucose uptake and overshoot with inward Na(+)-anion gradients. In Na(+)-equilibrated conditions, an inside-negative membrane potential difference (p.d.) produced by an inward Cl- gradient alone was capable of driving intravesicular [14C]glucose accumulation. The apparent anion conductance had a selectivity of Br- = I- = Cl- > F- > > gluconate, was inhibited by 0.5 mM 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) but was unaffected by 0.5 mM 4,4'-diisothiocyanatostilbene 2,2'-disulphonate (DIDS). BBMV were isolated from mice in which the CFTR gene had been disrupted by a termination mutation (-/-) and compared with normal litter mates (+/+) and heterozygotes (-/+)[18]. [14C]Glucose uptake in NaCl media was significantly greater than glucose uptake in Na gluconate media for all three genotypes measured at 20 s: for homozygous -/- animals [14C]glucose uptake was increased by 2.80 +/- 0.53 fold in Cl- media compared to gluconate media, n = 6; for wild-type +/+, by 2.16 +/- 0.53 fold, n = 8; and for heterozygous +/- animals, by 2.17 +/- 0.45 fold, n = 8. The observation of a Cl-(-)dependent component in BBMV isolated from homozygous -/- mutant animals shows that the chloride conductance in these vesicles cannot be due to CFTR expression.

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.

A candidate mouse model for Hartnup disorder deficient in neutral amino acid transport.

The mutant mouse strain HPH2 (hyperphenylalaninemia) was isolated after N-ethyl-N-nitrosourea (ENU) mutagenesis on the basis of delayed plasma clearance of an injected load of phenylalanine. Animals homozygous for the recessive hph2 mutation excrete elevated concentrations of many of the neutral amino acids in the urine, while plasma concentrations of these amino acids are normal. In contrast, mutant homozygotes excrete normal levels of glucose and phosphorus. These data suggest an amino acid transport defect in the mutant, confirmed in a small reduction in normalized values of 14C-labeled glutamine uptake by kidney cortex brush border membrane vesicles (BBMV). The hyperaminoaciduria pattern is very similar to that of Hartnup Disorder cases also show niacin deficiency symptoms, of Hartnup Disorder cases also show niacin deficiency symptoms, which are thought to be multifactorially determined. Similarly, the HPH2 mouse exhibits a niacin-reversible syndrome that is modified by diet and by genetic background. Thus, HPH2 provides a candidate mouse model for the study of Hartnup Disorder, an amino acid transport deficiency and a multifactorial disease in the human.

Characterization of a sodium-dependent concentrative nucleobase-transport system in guinea-pig kidney cortex brush-border membrane vesicles.

The characteristics of hypoxanthine transport were examined in purified brush-border membrane vesicles isolated from guinea-pig kidney. Hypoxanthine uptake in the vesicles was specifically stimulated by both Na+ and an inside-negative potential, resulting in a transient accumulation of intravesicular hypoxanthine. Na(+)-dependent hypoxanthine influx was saturable (apparent Km 4.4 +/- 2.1 microM, Vmax. 128 +/- 29 pmol/min per mg of protein at 100 mM NaCl and 22 degrees C). Guanine, thymine, 5-fluorouracil and uracil inhibited hypoxanthine uptake (Ki values 1-30 microM), but adenine and the nucleosides inosine and thymidine were without effect. Guanine competitively inhibited Na(+)-dependent hypoxanthine influx, suggesting that it was a substrate for the active nucleobase transporter in guinea-pig renal membrane vesicles. A sigmoidal dependence between hypoxanthine influx and Na+ concentration was obtained (KNa 13 +/- 2 mM; Hill coefficient, h, 2.13 +/- 0.14), suggesting that at least two Na+ ions are transported per hypoxanthine molecule. This system differs from the Na(+)-nucleobase carrier in cultured LLC-PK1 renal cells, which has a stoichiometric coupling ratio of 1:1. These results represent the first demonstration of an active electrogenic nucleobase carrier in renal apical membrane vesicles.

Localization of the Na +/H + exchanger isoform NHE-3 in rabbit and canine kidney

The distribution and subcellular localization of Na +/H + exchanger isoform NHE-3 was studied in rabbit and canine kidney using polyclonal antibodies to an NHE-3 fusion protein. Western blot analyses were performed against microsomal, brush-border, and basolateral membranes isolated from rabbit kidney cortex, outer medulla, and inner medulla. Immunoblots indicated that NHE-3 antibody recognized a strong band with 95–100 kDa molecular mass in cortical microsomes. Subcellular localization studies showed that NHE-3 was expressed in brush-border membranes of kidney cortex. Expression of NHE-3 in the medullary regions was studied by immunoblot analysis of NHE-3 antibody against the microsomal membranes from the outer and inner medulla. NHE-3 antibody specifically labelled a 95–100 kDa protein in outer but not inner medulla. Subcellular localization studies demonstrated that NHE-3 is localized to the brush-border membranes of the outer medulla. Immunoblot analysis against brush-border membranes from canine kidney cortex and outer medulla demonstrated the presence of an 83–90 kDa protein. The above experiments suggest that NHE-3 in rabbit kidney is a 95–100 kDa protein and is expressed in brush-border membranes of the cortex and outer medulla. The canine kidney NHE-3 is a 83–90 kDa protein and is expressed in brush-border membranes of the cortex and outer medulla. Based on its subcellular localization, we conclude that NHE-3 may be involved in vectorial Na + and HCO 3 − transport and pH o regulation.

Effect of low-phosphate diet on sodium/phosphate cotransport mRNA and protein content and on oocyte expression of phosphate transport.

Recently, we have isolated a complementary DNA most likely related to rabbit kidney cortex brush border membrane sodium/phosphate (Na/Pi) cotransport activity [NaPi-1 (1)]. To further elucidate the cellular mechanisms involved in dietary 'adaptation' of renal Na/Pi cotransport, we have exposed young rabbits for 2 weeks to either a low phosphate (Pi) diet (LPD) or a high Pi diet (HPD). Initial linear uptake of Na/Pi cotransport in isolated brush border membrane vesicles was increased in rabbits on a LPD compared with those on a HPD. Injection of equal amounts of total mRNA isolated from kidney cortex of LPD or HPD rabbits into Xenopus laevis oocytes resulted in a higher stimulation of Na-dependent oocyte Pi uptake in LPD than HPD preparations. No difference in the content of 'specific' mRNA (NaPi-1 cDNA probe, Northern blots) and of the content of the 'specific' brush border membrane protein (NaPi-1 antipeptide antibody, Western blots) between LPD and HPD preparations was observed. We conclude that 'chronic' dietary Pi deprivation leads to a protein synthesis-dependent alteration of Na/Pi cotransport activity which does not involve a change in the total amount of a protein related to the recently cloned NaPi-1 protein.

Subcellular localization of celiptium-induced peroxidative damage in rat renal cortex

Celiptium (N2-methyl-9-hydroxyellipticinium) is an antitumor agent of the ellipticine series. We have shown a dose-dependent nephrotoxicity in rats and demonstrated a lipid overload in proximal tubular cells (unsaturated free fatty acid accumulation). We have also shown an increase in thiobarbituric acid reactive substances (TBARS), namely the 4-hydroxyalkenals, that is paralleled by a decrease in phosphatidylethanolamine in rat kidney cortex. In the present study, peroxidative damage was localized in mitochondria, microsomal and brush-border membranes of kidney cortex. Female Wistar rats were injected with a single i.v. dose of 20 mg/kg celiptium and sacrificed on day 8. Subcellular fractionation studies showed that celiptium induced alterations: 1) in mitochondria (slight increase in aldehydes), 2) in microsomal membranes (increase in free fatty acids (FFA) with in particular rises in oleic (18:1) and linoleic (18:2) acids), 3) in brush-border membranes or BBM (decrease in protein and phospholipid contents); residual membranes showed an increase in oleic and linoleic acids and a decrease in the polyunsaturated fatty acids, arachidonic (20:4) and docosahexaenoic (22:6) acids, 4) in cytosol (increase in FFA and TBARS content). Thus, celiptium induces peroxidative damage in kidneys through lipid abnormalities which predominantly occur in brush-border membranes and consist of an increase in free fatty acids and aldehydes in cytosol.

Escherichia coli enterotoxin receptors: localization in opossum kidney, intestine, and testis

The distribution of receptors for Escherichia coli enterotoxin were examined in opossum kidney, intestine, and testis. E. coli enterotoxin stimulated guanosine 3',5'-cyclic monophosphate (cGMP) production in renal cortex, testis, and small intestinal mucosa but had only a small effect in the colon. Atrial natriuretic factor enhanced the cGMP content of renal cortex and small intestine but had no effect on testis or colon. The enterotoxin receptors were observed to be localized in proximal tubules, to epithelial cells of crypts and villi of small intestine, to crypts of colon, and in seminiferous tubules. Both convoluted and straight portions of proximal tubules exhibited specific binding sites for 125I-labeled enterotoxin. Glomeruli and distal tubules did not have receptors. Binding of 125I-enterotoxin to brush-border membranes of kidney cortex or intestinal mucosa and to testis membranes was markedly temperature dependent. The binding affinities of these receptors for E. coli enterotoxin were similar (i.e., IC50 approximately equal to 0.4-0.5 nM). Daily administration of 20 micrograms of enterotoxin intramuscularly to opossums increased urine cGMP excretion with no apparent changes in urine volume, Na+, or K+ excretion. Thus receptors for heat-stable enterotoxins are localized to proximal tubules of kidney and to enterocytes and seminiferous tubules of intestine and testis, respectively. Apical membranes may be the site of enterotoxin receptors in these epithelia.

LLC-PK1 cells express Na+-lactate cotransport in apical membranes after confluency.

L-[3H]lactate uptake was characterized in LLC-PK1 cell apical membrane vesicles obtained by intensive culture on microcarrier beads. The apical membrane preparation technique involved MgCl2 precipitation. Na+-dependent L-[3H]lactate uptake was present only after confluency; its appearance paralleled the subcellular localization of aminopeptidase in apical membranes. L-[3H]lactate uptake was Na+-dependent and electrogenic. Only the Na+-dependent component of L-[3H]lactate uptake was saturable with one family of independent carriers. The apparent affinity constant was 1.1 +/- 0.25 mM and the apparent maximal velocity was 29 +/- 3 nmol.mg-1.min-1. The Na+-lactate cotransport stoichiometry was 2 Na+ for 1 lactate. The specificity of the L-lactate transport system was compatible with that of the monocarboxylic acid pathway described previously in brush-border membranes of kidney cortex and discrete from the tricarboxylic acid carrier, the D-glucose transporter, and the general pathway for anions. The LLC-PK1 cell line appears to be a useful tool for study of the regulation of L-lactate uptake and biosynthesis of the renal monocarboxylic acid transporter.

Chloride dependence of the sodium-dependent glycine transport in pig kidney cortex brush-border membrane vesicles

The Na +-dependent glycine uptake in pig kidney cortex brush-border membrane vesicles is specifically enhanced by the presence of Cl −. The Na +-independent glycine uptake is not affected by Cl −. Various anions tested could not substitute Cl − in the activation of the Na +-dependent glycine transport. Cl − is specifically required on the outer membrane side. The Na +-dependent glycine uptake is higher in the presence of an inwardly directed Cl − gradient than the one measured in the presence of equilibrated Cl −. The Na +-dependent glycine uptake depends on, and is saturable at increasing Cl − concentrations. By studying the activation of glycine uptake by Na + in the presence and in the absence of Cl −, evidence was found that two different Na +-dependent glycine transport pathways are present in pig kidney cortex brush-border membrane vesicles. The kinetics of the glycine uptake measured in the presence of an inwardly directed NaCl gradient show the presence of two glycine transport systems, a low-affinity, high-capacity one and a high-affinity, low capacity one. In the absence of Cl − the high-affinity, low-capacity transport is almost suppressed, thus indicating the presence of a high-affinity glycine transport system simultaneously dependent on both Na + and Cl − ions.

Cysteine conjugate β-lyase activities in rat kidney cortex: Subcellular localization and relationship to the hepatic enzyme

Kidney cortex cysteine conjugate β-lyase enzymes were characterized using S -(2-benzothiazolyl)- L -cysteine and S -(1,2-dichlorovinyl)- L -cysteine as substrates. The contribution of the hepatic form of cysteine conjugate β-lyase to renal metabolism of these S -cysteine conjugates is not substantial. No cysteine conjugate β-lyase activity was found in kidney cortex brush border membrane vesicles. Two cysteine conjugate β-lyase activities with densities corresponding to the mitochondrial and soluble fractions were separated on Percoll gradients.