Immunocytochemical localization of gamma-glutamyl-transferase on isolated renal cortical tubular fragments

Phosphophloretin sensitivity of rabbit renal NaPi-IIa and NaPi-Ia

The effect of phosphorylated phloretins on Na+-dependent phosphate uptake into rabbit renal brush-border membrane vesicles (BBMV) was examined. Na+-dependent phosphate uptake into isolated rabbit cortex BBMV was sensitive to 2′-phosphophloretin (2′-PP) and 2′-phospho-4′,4,6′-trimethoxy phloretin (PTMP) in a dose-dependent and pH-dependent manner. PTMP inhibition of Na+-dependent phosphate uptake was maximum at alkali pH, and 2′-PP inhibition of Na+-dependent phosphate uptake was maximum at acidic pH. Increasing Na+concentrations did not increase PTMP inhibition of renal cortex BBMV Na+-dependent phosphate uptake at pH 6. The effect of phosphophloretins on Na+-dependent phosphate uptake was examined in BBMV isolated from purified proximal tubules and distal tubules. 2′-PP and PTMP inhibition of Na+-dependent phosphate uptake into BBMV isolated from purified proximal tubules was similar to the inhibition seen with BBMV from renal cortex. 2′-PP, but not PTMP, inhibited Na+-dependent phosphate uptake into BBMV isolated from purified distal tubules. The pH dependence of inhibition, the absence of PTMP inhibition of Na+-dependent phosphate uptake into distal tubule BBMV, and the inhibition of Na+-dependent phosphate uptake into distal tubule BBMV suggest that NaPi-Ia is 2′-PP sensitive and NaPi-IIa is PTMP sensitive.

Toxicity and transport of three synthesized mercury-thiol-complexes in isolated rabbit renal proximal tubule suspensions

Previous work has suggested that endogenous sulfhydryls, such as glutathione (GSH) and cysteine, are involved in the uptake and toxicity of HgCl2. To study this possibility, uptake and toxicity of synthesized Hg(SG)2, Hg(cysteinylglycine)2 [Hg(CYS-GLY)2] and Hg(CYS)2 were investigated in rabbit renal proximal tubule suspensions (RPT). The intracellular K+ was used as a toxicity indicator, and the mercury content in the tubules was measured by proton induced x-ray emission analysis. The toxicity rank order of the three synthesized mercury-thiol-complexes from the highest to the lowest was: Hg(CYS)2 > Hg(CYS-GLY)2 > Hg(SG)2. However, no significant difference among the mercury contents in the tubules exposed to these synthesized mercury-thiol-complexes was detected. Acivicin (0.25 mM), an inhibitor of gamma-glutamyltranspeptidase (GGT), decreased the toxicity of Hg(SG)2 in a manner that did not decrease the uptake of mercury in the tubules. This suggests that the toxicity of Hg(SG)2 requires processing to Hg(CYS-GLY)2 or Hg(CYS)2, while Hg(SG)2 may be taken up by the tubules via Na(+)-dependent GSH transporter since 10 mM acivicin, an inhibitor of this transporter dramatically decreased the uptake of Hg(SG)2. Organic anion transporter plays a minor role, if any, in the toxicity and uptake of Hg(SG)2 and Hg(CYS)2 since p-aminohippuric acid (PAH), an inhibitor of organic anion transporter, did not have significant effect on their uptake and toxicity. L-phenylalanine, an inhibitor of the neutral amino acid decreased the uptake of mercury, but to a lesser extent. This suggested that neutral amino acid transporter seemed to play a role, in part, in the toxicity and uptake of synthesized Hg(CYS)2. In summary, the data suggested that basolateral transport is important for the toxicity of the three synthesized mercury-thiol-complexes, and a variety of mechanisms are involved in the toxicity and uptake of these complexes in isolated rabbit RPT.

Characterization of a primary cell culture model of the avian renal proximal tubule

Methods have been developed for producing functional, transporting monolayers of avian proximal tubule (PT) cells. A highly homogenous fraction of PT fragments was prepared by enzymatic digestion (collagenase + Dispase) of chick (3- to 5-day-old) kidneys, followed by Percoll gradient centrifugation. The PT fraction was enriched in glucose-6-phosphatase, a proximal enzyme marker, and reduced in specific activity of hexokinase, a distal marker. PT fragments were grown to confluence in serum-free media on collagen-coated permeable filter supports. Electron microscopy of confluent monolayers revealed numerous microvilli and mitochondria, central cilia, and tight junctions, all characteristic of PT cells. gamma-Glutamyltranspeptidase, a proximal brush-border enzyme, showed threefold higher activity on apical than on basolateral sides of the monolayer. The electrophysiological characteristics of monolayers were investigated by voltage-clamp techniques. Monolayers displayed low transepithelial resistances (40-60 Omega . cm2), lumen-negative potentials, and baseline currents of 6-12 microA/cm2 (with or without 5 mM glucose). Both alpha-methyl-D-glucose (2 mM), a nonmetabolizable hexose, and phenylalanine (2 mM) significantly stimulated short-circuit current when added to the mucosal side of glucose-free monolayers. Phloridzin, a specific inhibitor of Na+-coupled glucose transport, significantly inhibited short-circuit current, as did 10(-5) M amiloride. Monolayers also expressed net secretory transport of urate. This cell culture preparation may provide a useful working model for the study of avian PT transport.

Glutathione and gamma-glutamyl transpeptidase are differentially distributed in the olfactory mucosa of rats

Components of the gamma-glutamyl cycle, including thiols, glutathione (GSH) and gamma-glutamyl transpeptidase (gamma-GT), were localized in the nasal mucosae of rats using histochemical and immunohistochemical methods. In olfactory mucosa, thiols were widely distributed, with intense staining in the mucociliary complex (MC), basal cells, acinar cells of Bowman's glands (BG), and olfactory nerve bundles, and with moderate staining in olfactory receptor neurons (ORNs). GSH was localized in MC, BG acinar cells, nerve bundles and, to a lesser extent, in ORNs. gamma-GT immunoreactivity was restricted to the MC and to basolateral and apical membranes of BG acinar and duct cells. The basolateral membrane of BG acinar cells, located in close association with blood vessels and connective tissue, showed granule-like immunoreactivity. In respiratory mucosa, all three compounds were localized in the MC and acinar cells of respiratory glands (RG). In the MC, gamma-GT immunoreactivity was associated primarily with brush borders of ciliated cells. Granular immunoreactivity was also apparent in the supranuclear region of RG acinar cells. These results demonstrate that components of the gamma-glutamyl cycle are localized in olfactory and respiratory glands, and that they are secreted into the mucus, where they may mediate perireceptor events such as detoxification and/or solubilization of air-borne xenobiotics, toxicants and odorants.

Metabolism and vascular effects of gamma-L-glutamyl-L-dopa on the isolated rat kidney

Gamma-L-glutamyl-L-dopa (or gludopa), a dopamine (DA) prodrug, is selectively metabolized in vivo by the kidney through the sequential action of two renal enzymes, gamma-glutamyl transpeptidase (gamma-GT) and aromatic L-amino acid decarboxylase (AADC). This study was designed to analyze, in vitro, the factors regulating gludopa metabolism and its renal vascular effects. Rat kidneys were perfused in closed circuit with a cell-free perfusion buffer containing 6% bovine serum albumin (BSA). Adding gludopa (final concentration 10(-5) M in the perfusate) led to the release of DA both into urine and perfusate (0.53 +/- 0.21 and 1.38 +/- 0.28 nmol/min/g kidney wt, respectively, during the first 5 min after substrate addition, N = 5, mean +/- SEM). Total DA release (urine plus perfusate) was 73.7 +/- 15.8 nmol/g kidney wt within 30 minutes of recirculation. In non-filtering kidneys, total DA release in the recirculating medium was lower (12.5 +/- 1.4 nmol/g kidney wt, P less than 0.01). Glomerular filtration and access to the gamma-GT on the brush border membrane of proximal tubular cells are therefore required for the maximal conversion rate of gludopa. On filtering kidneys, L-dopa was also converted to DA, but at a higher rate than gludopa (total DA formed within 30 min of recirculation = 131.2 +/- 31.9 nmol/g kidney wt) and this rate was not reduced in non-filtering kidneys (224.2 +/- 41.7 nmol/g kidney wt DA formed within 30 min). Metabolic conversion of L-dopa by AADC is thus preserved in the case of an approach via the basolateral side of the proximal tubular cells. The renal vascular effects of gludopa were studied after vascular tone had been restored by continuous perfusion of PGF2 alpha and after the inhibition of alpha- and beta-adrenoceptors. Gludopa (3.10(-6) to 4.10(-5) M) elicited concentration-dependent renal vasodilatation.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutathione uptake and protection against oxidative injury in isolated kidney cells

Analysis with radiotracer and high performance liquid chromatography techniques showed that glutathione (GSH) is transported intact into cells primarily of proximal tubule origin. Characteristics of GSH uptake were the same as previously reported for basal-lateral membrane vesicles, namely, uptake was Na+-dependent, inhibited by gamma-glutamylglutamate and/or probenecid, and not inhibited by cysteinylglycine or the constituent amino acids. Studies with inhibitors of gamma-glutamyltransferase (acivicin) and gamma-glutamylcysteine synthetase (buthionine sulfoximine) showed that GSH uptake, degradation and resynthesis are independent processes. The GSH uptake rate with 1 mM GSH was approximately three-fold greater than the GSH synthetic rate with 1 mM amino acids. To examine whether uptake of GSH can supplement synthesis to protect against injury, we incubated cells with a toxic concentration of t-butylhydroperoxide with or without GSH or its constituent amino acids. Although amino acids provided significant protection, GSH provided greater protection (cells with t-butylhydroperoxide plus GSH were not significantly different from cells alone). This protection by GSH was eliminated by gamma-glutamylglutamate or probenecid, indicating that GSH uptake was required for the protection seen. Protection was also eliminated when the GSSG reductase/GSH peroxidase system was inhibited by bischloronitrosourea (BCNU), indicating that GSH transport affords protection by maintaining GSH levels in the cell. Thus, intact GSH is transported into isolated proximal tubule cells by a Na+-dependent system, and this transported GSH can be used to supplement endogenous synthesis and GSSG reduction to protect cells against oxidative injury.

Changes of cerebral gamma glutamyltransferase activities after treatment with exogenous inducers

The activity of gamma-glutamyltransferase localized in isolated brain synaptic membranes- and microvessels-enriched fractions was assayed after treatment of rats with either phenobarbital or ethanol. Phenobarbital increased the activity of gamma-glutamyltransferase in microvessels, without alteration of synaptic membranes activity. An increase of enzyme activity was also obtained after a chronic intoxication with ethanol. These results suggest that the isoform of gamma-glutamyltransferase localized in brain microvessels may respond to exogenous inducers.

gamma-Glutamyl transpeptidase excretion in cisplatin-induced acute renal failure

Cisplatin (cisdiamminedichloroplatinum), an important antineoplastic agent, possesses nephrotoxicity as its major side effect. A mild partially reversible nonoliguric form of acute renal failure (ARF) is generally the most common form of nephrotoxicity and occurs in experimental animals following a single dose. gamma-Glutamyl transpeptidase (gamma GT) is an enzyme with maximal activity located in the brush border of proximal renal tubular epithelium. To test the relationship between cisplatin nephrotoxicity and urinary gamma GT excretion, rats received a single 5.5 mg/kg dose of cisplatin and gamma GT excretion was evaluated and compared to anatomic and functional damage. Twenty-four hours following cisplatin administration, there was a marked enhancement of urinary gamma GT excretion, prior to the onset of azotemia. Urinary gamma GT excretion peaked at day 4, then returned to baseline, and decreased to values below baseline on days 8 through 10. By days 11 through 12, renal function and urinary gamma GT excretion had returned to normal. The correlation between nephrotoxicity, changes in urinary gamma GT excretion, and anatomic damage was excellent. Morphologically, increased gamma GT excretion was associated with loss of microvilli, and the return of urinary gamma GT excretion to normal correlated with their regeneration. We conclude that cisplatin administration results in increased urinary gamma GT excretion. This early enhancement, prior to the onset of azotemia, may provide a useful noninvasive marker of early cisplatin nephrotoxicity.

Ammoniagenesis catalyzed by hippurate-activated gamma-glutamyltransferase in the lumen of the proximal tubule. A microperfusion study in rat kidney in vivo

gamma-Glutamyltransferase (gamma-GT) is located in the brushborder membrane of the proximal tubule where the catalytic site of the enzyme faces the lumen. The (phosphate-independent) glutaminase activity of gamma-GT in vitro is activated by hippurate. In order to investigate glutamine deamidation in the tubule lumen in vivo, 14C-L-glutamine-containing solutions were continuously microperfused through sections of the proximal convoluted tubule in vivo and in situ. D-aspartate and L-phenylalanine (10 mmol/l, each) were added to the perfusate in order keep the reabsorption of L-glutamine as such low and to block reabsorption of any glutamate possibly formed, respectively. Intraluminal formation of glutamate from glutamine in the absence of hippurate is small. In presence of 10 mmol/l hippurate, 5%-70% of the recovered 14C-activity was 14C-glutamate at an initial 14C-L-glutamine concentration of 1 mmol/l. The respective absolute rate (+/- SEM) of glutamate formation, i.e., 36 +/- 5 pmol X s-1 X m-1, was increased 1.4-fold at an initial L-glutamine concentration of 3 mmol/l, but dropped to one third at initially 0.3 mmol/l. A rough estimate of the apparent kinetic constants resulted in a Km of 0.58 (0.19-0.97) mmol/l and a Vmax of 56 (40-93) pmol X s-1 X m-1. Deamidation of glutamine occurred also in the absence of L-phenylalanine. Acivicin (AT 125), a gamma-GT inhibitor, completely blocked glutamate formation. Endogenous hippurate concentrations determined by free flow micropuncture and HPLC were 0.16 mmol/l in the late proximal convolution, 0.6 mmol/l in the early distal convolution, and 4.9 mmol/l in the final urine.(ABSTRACT TRUNCATED AT 250 WORDS)

Histochemical demonstration of peptidases in the human kidney

The localization of several peptidases in the human kidney was investigated histochemically. The membrane-bound peptidases, aminopeptidase A (APA), aminopeptidase M, gamma-glutamyltransferase (gamma-GT) and dipeptidylpeptidase IV, were mainly demonstrable in the brush border of the proximal tubule. In addition, APA was found in the glomeruli, while gamma-GT was found in the basal labyrinth of the proximal tubule. The lysosomal peptidases, dipeptidylpeptidase I and cathepsin B, were most strongly concentrated in the different-sized lysosomes of the proximal tubule, but they were also found in the small lysosomes of the distal tubule. Dipeptidylpeptidase II showed only a weak reaction in lysosomes of the proximal tubule. It is concluded that, in comparison with other previously studied species, the human kidney has a well-developed equipment with membrane-bound and lysosomal peptidases.

Identification of proximal tubule segments in the mouse nephron by simultaneous visualization of alkaline phosphatase and gamma-glutamyl transpeptidase

ALP and gamma-GT are 2 brush border enzymes that can be individually demonstrated on adjacent sections by the histochemical methods of Mayahara (ALP) and Rutenberg (gamma-GT). On the basis of each enzyme activity, it was possible to recognize different categories of tubules in the mouse nephron. In fact, both enzymes were heterogeneously distributed along the proximal tubule, but in opposite gradients. The various staining intensities probably corresponded to proximal segmentation, but were sometimes difficult to evaluate. A technique was perfected to localize both enzymes in the same tissue section. Since each enzyme produced a distinct type of colored precipitates (ALP: black, gamma-GT: red), 4 categories of tubules could be identified, according to staining characteristics: 1. black tubules where ALP activity was predominant, corresponded to S1 segments, 2. black and red tubules where the 2 activities were about equivalent, were considered as parts of S2, 3. red ones where gamma-GT activity was high, were identified as portions of S3, 4. negative tubules where no activity was apparent, represented distal and straight collecting tubules. In addition to economize time and tissue, this simple technique permits to easily estimate variations in enzyme activities that probably correspond to structural and functional differences in the segments of the proximal tubule.