A simple method for the isolation of basolateral plasma membrane vesicles from rat kidney cortex. Enzyme activities and some properties of glucose transport

A Novel Cell Membrane-Associated RNA Extraction Method and Its Application in the Discovery of Breast Cancer Markers

Cell membrane-associated RNA (mem-RNA) has been demonstrated to be cell-specific and disease-related and are considered as potential biomarkers for disease diagnostics, drug delivery, and cell screening. However, there is still a lack of methods specifically designed to extract mem-RNA from cells, limiting the discovery and applications of mem-RNA. In this study, we propose the first all-in-one solution for high-purity mem-RNA isolation based on two types of magnetic nanoparticles, named MREMB (Membrane-associated RNA Extraction based on Magnetic Beads), which achieved ten times enrichment of cell membrane components and over 90% recovery rate of RNA extraction. To demonstrate MREMB's potential in clinical research, we extracted and sequenced mem-RNA of typical breast cancer MCF-7, MDA-MB-231, and SKBR-3 cell lines and non-neoplastic breast epithelial cell MCF-10A. Compared to total RNA, sequencing results revealed that membrane/secreted protein-encoding mRNAs and long noncoding RNAs (lncRNAs) were enriched in the mem-RNA, some of which were significantly overexpressed in the three cancer cell lines, including extracellular matrix-related genes COL5A1 and lncRNA TALAM1. The results indicated that MREMB could enrich membrane/secreted protein-coding RNA and amplify the expression differences of related RNAs between cancer and non-neoplastic cells, promising for cancer biomarker discovery.

Quantitative Targeted Absolute Proteomics for 28 Transporters in Brush-Border and Basolateral Membrane Fractions of Rat Kidney

The purpose of the present study was to determine the absolute protein expression levels of various transporters in renal brush-border membrane (BBM) and basolateral membrane (BLM) fractions, in order to understand the quantitative differences in average transport activities among different transporters at each cellular membrane. BBM and BLM fractions of rat kidney were prepared and digested with trypsin, and simultaneous absolute quantification of 28 transporters and a BLM marker, Na(+)/K(+)-ATPase, was performed using our established quantitative-targeted absolute proteomics (QTAP) technique. In BBM fraction, the protein expression levels of bcrp, urat1, mate1, octl1, mrp4, mdr1a, and abca3 were 40.3, 22.2, 8.90, 4.85, 4.69, 3.22, and 0.976 fmol/μg protein, respectively. In BLM fraction, the protein expression levels of oat1, oat3, oct1, mrp6, and mrp1 were 10.6, 10.2, 4.59, 0.724, and 0.271 fmol/μg protein, respectively. The expression levels of abca2, abca4, abca5, abca12, abcb4, mrp5, abcc9, abcg1, abcg5, lat1, ntcp, pgt, oatp2b1, oatp1b2, oatp3a1, and oct3 were under the limit of quantification in both fractions. The quantitative transporter protein expression profiles at these membranes, as determined by QTAP analysis, should be helpful to understand the contributions of individual transporters to renal excretion of xenobiotics and endogenous compounds.

Modulated pharmacokinetics and increased small intestinal toxicity of methotrexate in bilirubin-treated rats

OBJECTIVES

The effect of bilirubin treatment on the pharmacokinetics and small intestinal toxicity of methotrexate was evaluated in rats, since bilirubin and its glucuronide conjugates can suppress multidrug resistance-associated protein-mediated transport.

METHODS

Rats were treated intravenously with bilirubin and the various clearances and tissue distribution of methotrexate were estimated under a steady-state plasma concentration. Intestinal toxicity induced by methotrexate was also evaluated by measuring the leakage of alkaline phosphatase (ALP) activity. Probenecid, an inhibitor for multidrug resistance-associated protein and organic anion transporters, was used for comparison.

KEY FINDINGS

The treatment with bilirubin increased the steady-state plasma concentration and reduced biliary excretion clearance, urinary excretion clearance and intestinal exsorption clearance of methotrexate, as did treatment with probenecid. The intestinal absorption and jejunum distribution of methotrexate also significantly increased in bilirubin- and probenecid-treated rats. A greater leakage of ALP activity to the luminal fluid, with a lower ALP activity in the intestinal mucosal membrane after intestinal perfusion of methotrexate, was observed in bilirubin- and probenecid-treated rats.

CONCLUSIONS

Hyperbilirubinemia, which is involved under various disease states, may increase the small intestinal accumulation and toxicities of methotrexate, since high plasma concentrations of conjugated bilirubin can suppress the function of multidrug resistance-associated proteins, which facilitate the efflux of methotrexate out of cells.

Function of multidrug resistance-associated protein 2 in acute hepatic failure rats

The function of multidrug resistance-associated protein 2 (Mrp2) in the intestine and liver, as well as intestinal Mrp2 expression, was analyzed in CCl(4)-induced acute hepatic failure rats with hyperbilirubinemia. The plasma level of bilirubin glucuronides, endogenous Mrp2-substrates, was 26 microM at 24 h after CCl(4) treatment. Mrp2 protein levels in jejunum decreased to 41% of control level. Mrp2-mediated efflux of 2,4-dinitrophenyl-S-glutathione (DNP-GSH), an Mrp2-substrate, in jejunum decreased to 31% of control in vitro, and was almost completely suppressed in vivo to the same level as that in the presence of probenecid, an Mrp2-inhibitor. Biliary excretion of DNP-GSH was suppressed to the same level as that inhibited by intravenous probenecid. The suppression of Mrp2 and the increased plasma bilirubin glucuronides recovered within 24 h thereafter. These results suggest that hyperbilirubinemia in disease states may be related to the systemic suppression of Mrp2 function.

Major role of organic anion transporters in the uptake of phenolsulfonphthalein in the kidney

Phenolsulfonphthalein is used for testing renal function. However, its excretion mechanism has not been elucidated. The purpose of this study was therefore to elucidate the transporter-mediated excretion system for phenolsulfonphthalein. p-Aminohippuric acid, a substrate of rat organic anion transporter1 (rOat1), and cimetidine, a substrate of rOat3, reduced the urinary excretion of phenolsulfonphthalein. The uptake of phenolsulfonphthalein by kidney slices was found to consist of two components. The IC50 values of rOat1 substrates were higher than those of rOat3 substrates. In the presence of cimetidine, the Eadie-Hofstee plot gave a single straight line. The profile of the phenolsulfonphthalein uptake component in the presence of cimetidine was similar to that of the low-affinity component in the absence of cimetidine. We conclude that rOat1 and rOat3 are involved in the renal uptake of phenolsulfonphthalein and that phenolsulfonphthalein is a high-affinity substrate for rOat3 but is a relatively low-affinity substrate for rOat1.

Cloning and characterization of a novel Na+-dependent glucose transporter (NaGLT1) in rat kidney

To identify novel transporters in the kidney, we have constructed an mRNA data base composed of 1000 overall clones by random sequencing of a male rat kidney cDNA library. After a BLAST search, approximately 40% of the clones were unknown and/or unannotated and were screened by measuring the uptake of various compounds using Xenopus oocytes. One clone stimulated the uptake of alpha-methyl-d-glucopyranoside and therefore was termed rat Na(+)-dependent glucose transporter 1 (rNaGLT1). The rNaGLT1 cDNA (2173 bp) has an open reading frame encoding a 484-amino acid protein, showing <22% homology to known SGLT and GLUT glucose transporters. alpha-Methyl-d-glucopyranoside uptake by rNaGLT1 cRNA-injected oocytes showed saturability, with an apparent K(m) of 3.7 mm and a coupling ratio of 1:1 with Na(+). rNaGLT1 mRNA was expressed predominantly in the kidney upon Northern blot analysis and reverse transcription-PCR. Reverse transcription-PCR in microdissected nephron segments revealed that rNaGLT1 mRNA was primarily localized in the proximal tubules. A clear signal corresponding to rNaGLT1 protein was recognized in the brush-border (but not basolateral) membrane fraction by immunoblot analysis. The rNaGLT1 mRNA level in the kidney was significantly higher than rat SGLT1 and SGLT2 mRNA levels. These findings suggest that rNaGLT1 is a novel Na(+)-dependent glucose transporter with low substrate affinity that mediates tubular reabsorption of glucose.

Differential regulation of Na(+),K(+)-ATPase and the Na(+)-coupled glucose transporter in hypertensive rat kidney

Several Na(+) transporters are functionally abnormal in the hypertensive rat. Here, we examined the effects of a high-salt load on renal Na(+),K(+)-ATPase and the sodium-coupled glucose transporter (SGLT1) in Dahl salt-resistant (DR) and salt-sensitive (DS) rats. The protein levels of Na(+),K(+)-ATPase and SGLT1 in the DS rat were the same as those in the DR rat, and were not affected by the high-salt load. In the DS rat, a high-salt load decreased Na(+),K(+)-ATPase activity, and this decrease coincided with a decrease in the apparent Mechaelis constant (K(m)) for ATP, but not with a change of maximum velocity (V(max)). On the contrary, a high-salt load increased SGLT1 activity in the DS rat, which coincided with an increase in the V(max) for alpha-methyl glucopyranoside. The protein level of phosphorylated tyrosine residues in Na(+),K(+)-ATPase was decreased by the high-salt load in the DS rat. The amount of phosphorylated serine was not affected by the high-salt load in DR rats, and could not be detected in DS rats. On the other hand, the amount of phosphorylated serine residues in SGLT1 was increased by the high-salt load. However, the phosphorylated tyrosine was the same for all samples. Therefore, we concluded that the high-salt load changes the protein kinase levels in DS rats, and that the regulation of Na(+),K(+)-ATPase and SGLT1 activity occurs via protein phosphorylation.

Assay of ATPase and Na,K-ATPase activity using high-performance liquid chromatographic determination of ADP derived from ATP

An HPLC assay for determination of ATPase activity was developed and validated. After stopping the enzyme reaction of the enzyme source (rat renal cortical basolateral membranes) with ATP, products derived from ATP were analyzed by two methods; HPLC determination of ADP derived from ATP, and colorimetry of inorganic phosphorus (Pi) released from ATP. This HPLC procedure was precise and linear over the range of protein amount of the enzyme source studied, and the intra-and inter-assay variations were lower than 10%. The values that were obtained by the two methods revealed a significant correlation. Also, even when the samples contained Pi or were contaminated with Pi, this HPLC method allowed determination of ATPase activity. In addition, when ouabain was used as an inhibitor, the HPLC method was found to be applicable for Na,K-ATPase determination. This indicated that this HPLC assay would enable determination of ATPases other than Na,K-ATPase, when other inhibitors are employed instead of ouabain.

Role of apoptosis in cisplatin-induced toxicity in the renal epithelial cell line LLC-PK1. Implication of the functions of apical membranes

The role of apoptosis and the implications of the functions of apical membranes in cisplatin-induced nephrotoxicity were investigated using the kidney epithelial cell line LLC-PK1. When LLC-PK1 cells were treated with 30 microM cisplatin, the number of floating cells was increased markedly. However, the number was not increased by treatment with 1 mM cisplatin, suggesting that different mechanisms were involved in the toxicities of these two treatments. DNA fragmentation, condensation of nuclear chromatin, and the absence of trypan blue staining suggested that cellular toxicity following treatment with 30 microM cisplatin for 24 hr was mediated predominantly by apoptosis. Specific activities of apical enzymes (gamma-glutamyltransferase, EC 2.3.2.2; and alkaline phosphatase, EC 3.1.3.1) in LLC-PK1 cells were decreased markedly by treatment with 30 microM cisplatin for 24 hr, whereas neither lactate dehydrogenase (LDH; EC 1.1.1.27) release nor a decrease in cellular protein content was observed following the same treatment. In addition, concomitant treatment with reduced glutathione completely attenuated both the apoptosis and the decrease of apical enzyme activities induced by 30 microM cisplatin. Neither DNA fragmentation nor condensation of chromatin was induced by treatment with 1 mM cisplatin for 12 hr. However, LDH release and a decrease in cellular protein level were induced by 1 mM cisplatin, suggesting that the toxic effect was due to necrosis. Under these conditions, specific activities of apical enzymes were not decreased. These results suggested that apoptosis was more responsible than necrosis for the loss of apical functions in cisplatin-induced toxicity in LLC-PK1 cells.

Gender differences in expression of organic cation transporter OCT2 in rat kidney

The organic cation transporter (OCT) mediates translocation of various cationic molecules including drugs, toxins and endogenous substances. We examined gender differences in the expression of rat (r) OCT2 in the kidney. Slices and basolateral membrane vesicles of male rat kidney showed a higher transport activity for tetraethylammonium than those of female rat kidney. The expression levels of rOCT2 mRNA and protein in the kidney of males were much higher than those in females. There was no gender difference in mRNA expression of rOCT1 and rOCT3. These findings suggest that rOCT2 is responsible for the gender differences in renal basolateral membrane organic cation transport activity.

Cisplatin-induced toxicity in LLC-PK1 kidney epithelial cells: role of basolateral membrane transport

Cytotoxicity of cisplatin was evaluated after apical and/or basolateral treatment of LLC-PK1 cell monolayers grown on porous membrane filters with 300 microM cisplatin. When LLC-PK1 cells were exposed from basolateral side for 0.5-4 h, lactate dehydrogenase (LDH) release into culture medium was markedly stimulated. However, apical treatment of the cells with cisplatin for 0.5 h did not stimulate LDH release. gamma-Glutamyltransferase activity and amount of protein in the cell homogenate were markedly decreased by basolateral treatment with cisplatin. However, in the apical treatment with cisplatin, these changes were relatively small, suggesting that degrees of the toxicities were different between basolateral and apical treatment with cisplatin. Cellular platinum level after basolateral treatment with cisplatin was higher compared to that following apical treatment. Furthermore, both accumulation and toxicity of cisplatin in LLC-PK1 cells were decreased by treatment with cisplatin at 4 degrees C. These results suggested that there were specific mechanisms mediating cisplatin uptake at the basolateral membranes of LLC-PK1 cells.

Synthesis and properties of an EGF-like domain (residues 361-406) in the extreme N-terminal region of the mouse EGF precursor

Various proteins contain EGF-like domains that are not ligands for the EGF receptor. In the present study a cognate polypeptide for residues 361-406 of the mouse EGF precursor was synthesized by the solid-phase method. The product was renatured under oxidative conditions since it probably has an EGF-like array of three cystine disulfide bonds in its native state. HPLC analysis of the renaturation reaction revealed formation of a peak material with no apparent free-SH groups. Accordingly, the HPLC retention time of this product was readily increased by treatment (reduction of disulfides) with dithiothreitol. The renatured 46-mer (PEGF-1) did not displace 125I-EGF bound to rat liver membranes and 125I-PEGF-1 did not exhibit specific binding to membrane preparations from the mouse liver, mammary gland, or kidney, with or without Ca2+ in the binding medium. Although PEGF-1 contains a putative Ca2+ binding motif, specific binding of this cation by the polypeptide could not be demonstrated by electromobility shiff or incubation with 45Ca2+. Immunoassay of PEGF-1 and EGF in fractions obtained following gel filtration of mouse urine revealed multiple peaks of PEGF-1 immunoreactivity with the major peaks eluting at an Mr > 30 kDa. In contrast, virtually all the EGF immunoreactivity eluted at a volume similar to that of 125I-EGF. These data suggest that selective cleavage of the PEGF-1 domain from the precursor does not occur with the proclivity known for that of EGF. Instead, the PEGF-1 probably functions coordinately with other EGF-like domains while tethered to the precursor backbone. Finally, localization of PEGF-1 immunoreactivity occurred only in cell populations of the mouse previously demonstrated as sites for EGF/EGF precursor, which suggests that PEGF-1 is exclusively a domain of the EGF precursor.

Stereoselective renal secretion of carbenicillin in rabbits: role of the organic anion transporter at the renal brush border membrane

Stereoselectivity in the renal secretion of carbenicillin (CBPC) was studied in rabbits. Significant renal secretion of CBPC was observed in vivo, with the secretion of the S-epimer being greater than that of the R-epimer. Stereoselective transport of CBPC was further studied in vitro using basolateral and brush border membrane vesicles prepared from rabbit kidneys. The transport of CBPC by the organic anion transporter into the basolateral membrane vesicles (BLMV) was not stereoselective. In contrast, a distinct stereoselectivity was observed in the transport of CBPC by the organic anion transporter into the brush border membrane vesicles (BBMV), with the transport of the S-epimer being more favorable. Significant epimer-epimer interactions were also observed in the transport into BBMV. The stereoselectivity of the transport of CBPC was calculated from the kinetic parameters with consideration of epimer-epimer interactions and was similar to that observed in vivo. It was concluded that the observed stereoselectivity in the renal secretion of CBPC in vivo reflected that of transport via the organic anion transporter located at the brush border membrane.

Differences in binding of epidermal growth factor to liver membranes of TCDD-resistant and TCDD-sensitive rats after a single dose of TCDD

Epidermal growth factor (EGF) receptor has been implied as having a role in certain actions of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). After a single dose of TCDD, the receptor has been shown to be downregulated in several tissues including the liver. Two rat substrains, the Han/Wistar (Kuopio; H/W) rat and the Long-Evans (Turku AB; L-E) rat exhibit over a 1000-fold difference in their sensitivity to the lethal effect of TCDD. This large sensitivity difference was utilized in the current study to investigate whether or not a correlation exists between TCDD lethality and biochemical endpoints related to the hepatic EGF receptor. In the TCDD-sensitive L-E strain both the B(max) of the EGF receptor and the receptor protein as measured by Western blots, decreased dose and time dependently. Ten days after a lethal dose of TCDD (50 μg/kg), the downregulation was 80%. In the resistant H/W strain, two non-lethal doses were used (50 and 500 μg/kg), since the lethal dose is not known. These doses caused a downregulation already at 4 days after dosing, but no further decrease by day 10. The activity of phosphoenolpyruvate carboxykinase (PEPCK, the main gluconeogenetic enzyme in the liver and a proposed target of TCDD) decreased in H/W rats at least to the same extent as in L-E rats at both 4 and 10 days. It is concluded that EGF receptor downregulation is different in the two rat strains studied, despite the fact that a classical Ah receptor-regulated response (CYP1A1 induction) is similar. The results demonstrate that downregulation of the EGF receptor by TCDD is strain-dependent as well as dose- and time-dependent.

Alpha 2-adrenoceptors in brain and kidney during development of hypertension in Dahl-Iwai salt-sensitive rats

BACKGROUND

Both renal and extrarenal factors have been considered to contribute to the development of hypertension in Dahl salt-sensitive rats, but contents of both factors have not been established precisely.

AIM

To clarify the role of those factors in the sympathetic nervous system, we examined the regulation of alpha2-adrenoceptors in the lower brainstem and the renal tubular basolateral membranes simultaneously during the development of salt-induced hypertension in Dahl-Iwai salt-sensitive rats.

METHODS

Dahl-Iwai salt-sensitive or resistant rats were fed a high (8.0% NaCl)- or low (0.3%)- salt diet from 4 to 6 or 10 weeks of age. At 4, 6 and 10 weeks of age, the plasma membranes of the lower brainstem and the renal tubular basolateral membranes were obtained simultaneously and alpha 2-adrenoceptors were quantified by a radioligand binding assay using 3H-rauwolscine.

RESULTS

In the salt-sensitive rats, systolic blood pressure was significantly higher in those fed a high-salt diet than in those fed a low-salt diet. In the salt-resistant rats, both the high- and the low-salt groups showed similar blood pressure levels. At 6 weeks of age, alpha 2-receptor densities of the salt-sensitive rats fed a high-salt diet were lower in the lower brainstem and higher in the renal basolateral membranes than those fed a low-salt diet. In contrast, in the salt-resistant rats, both the high- and the low-salt groups had similar densities. At 10 weeks of age, the difference between the high- and the low-salt groups in the salt-sensitive rats disappeared in both the brainstem and the renal basolateral membranes.

CONCLUSIONS

Alpha 2-adrenoceptor regulation in the brainstem and the renal basolateral membranes differs between Dahl-Iwai salt-sensitive and salt-resistant rats. The modulation of alpha 2-adrenoceptors by a high salt intake may be essential particularly in the early phase of the development of salt-induced hypertension.

Transport of organic cation in renal brush-border membrane from rats with renal ischemic injury

Transport of tetraethylammonium, an organic cation has been studied using renal brush-border membrane vesicles isolated from rats with ischemic and ischemia-reperfusion injury. H+ gradient-dependent uptake of tetraethylammonium slightly, but significantly, decreased in brush-border membrane vesicles from ischemic kidneys. When the kidney was reperfused after ischemia, the extent of the decrease of tetraethylammonium uptake was much greater than that after ischemia alone. The Vmax value of tetraethylammonium uptake by brush-border membrane vesicles from reperfused kidneys was decreased compared with control, without any change in the Km value. The tetraethylammonium uptake by the vesicles from reperfused kidneys was decreases both in the presence and absence of the outward H+ gradient (driving force). Uptake of D-glucose in renal brush-border membrane vesicles was also decreased by ischemia and again, reperfusion caused a further decrease of the uptake. Reperfusion also induced marked changes in the enrichment and recovery of marker enzymes in the isolated brush-border membrane fraction compared with ischemia. These findings suggest that renal ischemic injury altered the transport properties of tetraethylammonium as well as D-glucose, and that reperfusion after ischemia induced further damages on these functions in the brush-border membrane.

Characteristics of organic cation transporter in rat renal basolateral membrane

Characteristics of organic cation transport system were studied in rat renal basolateral membrane and compared with those in brush-border membrane. We first examined the effect of various chemical modifiers on tetraethylammonium uptake by the membrane vesicles. Treatment with N,N'-dicyclohexylcarbodiimide and phenylglyoxal (carboxyl groups and arginine residues specific reagent, respectively) resulted in inhibition of tetraethylammonium transport in both basolateral and brush-border membranes. Tetraethylammonium uptake by brush-border, but not by basolateral, membrane vesicles was decreased by diethyl pyrocarbonate, histidine residues specific reagent, treatment. Treatment of sulfhydryl groups with HgCl2 decreased tetraethylammonium transport in both membranes. However, in contrast to brush-border membrane, unlabeled tetraethylammonium failed to protect against the inhibition of [14C]tetraethylammonium uptake by p-chloromercuribenzene sulfonate in basolateral membrane. We next examined the inhibitory effect of various organic cations on tetraethylammonium uptake. The order of inhibitory potency of organic cations was somewhat different between two membranes. These findings suggest that the characteristics of organic cation transport systems in basolateral and brush-border membranes were different in regard to essential amino acid residues and the affinity of substrates.

Purification of brush border membrane vesicles from rat renal cortex by size-exclusion chromatography

Size-exclusion chromatography with controlled pore glass (CPG) was used in the further purification of renal brush border membrane vesicles (BBMV) isolated by the Ca precipitation method. The BBMV obtained had an almost spherical shape and their average diameter was about 95 nm in isotonic solution. The specific activities of alkaline phosphate and leucine aminopeptidase in the BBMV preparation were increased 18- and 17-fold, respectively, over those in the crude homogenate. The uptake of D-glucose by the purified BBMV in the presence of a sodium gradient reached 8.53 nmol/mg protein at 20 s. These results indicate that CPG chromatography is suitable procedure by which to obtain purified renal BBMV of homogenous size and with high specific marker enzyme activity for use in the study of membrane transport.

Hepatic lipid peroxidation, sulfhydryl status, and toxicity of the blue-green algal toxin microcystin-LR in mice

Microcystin-LR (MCLR), a cyclic heptapeptide produced by the blue-green algae Microcystis aeruginosa, produces death in female mice treated with 100 micrograms MCLR/kg. Kupffer-cell hyperplasia was observed histologically after treatment with 50 or 100 micrograms MCLR/kg. No other changes or lethality were observed with the 50 micrograms MCLR/kg, while 100% lethality occurred in less than 2 h in mice treated with 100 micrograms/kg. In these animals liver weights increased by 45% and hepatic hemoglobin content increased 106% at 60 min posttreatment. Liver histology showed loss of hepatic architecture and necrosis 30 min after treatment, and congestion with blood became evident at 45 min after treatment. Serum enzymes were significantly increased 45 min posttreatment. Hepatic nonprotein sulfhydryl content decreased 19% when calculated on the basis of cytosolic protein and 39% when based upon the total protein content, respectively. The sulfhydryl content of the liver cytoskeletal fraction decreased 26% by 30 min after treatment. Decreased enzyme-mediated and increased non-enzyme-mediated lipid peroxidation were observed in hepatic microsomes following both in vivo and in vitro exposure of hepatic microsomes to MCLR. The toxicity of MCLR may be related to alterations in the sulfhydryl content of the cytoskeletal protein. Furthermore, MCLR may either directly or indirectly affect microsomes, suggesting alterations in structure and function of smooth endoplasmic reticulum.

Studies on the nephrotoxicity of aminoglycoside antibiotics and protection from these effects (9): Protective effect of inositol hexasulfate against tobramycin-induced nephrotoxicity

We examined the protective effect of inositol hexasulfate (IS6) against tobramycin (TOB)-induced nephrotoxicity. In the electrophoretic analysis, TOB alone and IS6 alone were observed as single spots on the cathode and anode sides, respectively. However, in the mixture of TOB and IS6 preincubated at 37 degrees C for 3 hr, the tailing of the spots of TOB and IS6 were observed from the origin to the cathode and the anode sides, respectively, and the overlapping of the spots of TOB and IS6 was recognized at the origin. These results indicated that TOB directly interacted with IS6 in vitro. Assay of TOB binding to rat kidney brush border membranes (BBMs) indicated that IS6 inhibited the binding of TOB to BBMs through an interaction of TOB and IS6. No significant reduction in intrarenal TOB level was observed in the rats given TOB (90 mg/kg, s.c.) and IS6 (153 or 610 mg/kg, s.c.). However, the treatment of rats with a combination of TOB and IS6 reduced the degree of necrosis of renal tubular cells and also suppressed the increases in urinary protein, urinary enzyme activities, blood urea nitrogen and plasma creatinine induced by TOB. Additionally, we detected a complex of TOB and IS6 in the urine of rats given both compounds simultaneously. These results indicate that IS6 protects against TOB-induced nephrotoxicity and that the protective action of IS6 may be due to the inhibition of TOB binding to BBMs through an interaction of TOB with IS6.

Simultaneous preparation of basolateral and brush-border membrane vesicles from sea bass intestinal epithelium

A method is described for simultaneous preparation of brush-border and basolateral sea bass enterocyte membranes using simple differential centrifugation and discontinuous sucrose gradient density centrifugation techniques. Basolateral membranes were purified with a Na+/K(+)-ATPase yield of about 11% of the original activity, with an enrichment factor of 12. The yield of maltase-glucoamylase, a specific marker of brush-border membranes, was also about 11% of the original activity, with 15-fold enrichment. The characteristics of these membrane preparations were determined. Electron microscopy analysis showed that these two membrane preparations were uniform in size and vesicular in nature. Orientation studies revealed that the luminal membrane vesicles were right-side out and 43% of the antiluminal membrane vesicles were sealed inside out. Investigation of D-glucose and L-leucine uptake showed that these two plasma membrane preparations retained their transport properties.

Transport of cephalosporin antibiotics in rat renal basolateral membranes

Transport mechanisms of cephalosporin antibiotics in rat renal basolateral membranes have been studied in isolated membrane vesicles. Uptake of [14C]p-aminohippurate, a typical organic anion, by basolateral membrane vesicles was enhanced when membrane vesicles were preloaded with unlabelled p-aminohippurate (counter-transport). Cephalosporins such as cephradine, cephalexin, and cefazolin inhibited the counter-transport of [14C]p-aminohippurate, as did unlabelled p-aminohippurate and probenecid. In contrast, cephalexin did not affect the uptake of [3H]tetraethylammonium, an organic cation, by basolateral membrane vesicles. These results suggest that most cephalosporins are transported via organic anion transport systems in rat renal basolateral membranes.

Atrial peptide inactivation by rabbit-kidney brush-border membranes

Atriopeptin (AP) 24, containing amino acids Ser103-Tyr126 of the carboxy-terminal portion of the atrial natriuretic peptide prohormone, was degraded rapidly by rabbit kidney brush border membranes. The rate of degradation of AP24 measured by the loss of vasorelaxant activity followed a similar time course to the decrease in peptide peak area measured by high-performance liquid chromatography. Inactivation of AP24 produced peptide fragments which were separated by HPLC. The major products were purified individually and their peptide sequences determined. Results indicate that AP24 was proteolytically cleaved at three peptide bonds: Ser103-Ser104, Cys105-Phe106 and Ser123-Phe124. des-Ser103-AP24 had similar vasorelaxant activity to AP24, while AP24 cleaved at Cys105-Phe106 was inactive. Regarding the proteolytic cleavage at Ser123-Phe124, there was an accumulation of the C-terminal tripeptide, Phe-Arg-Tyr, only at the later time points of the incubation. Degradation experiments were repeated with an amino- and carboxy-terminal protected peptide, acetyl-AP24-amide. Peptide sequence analysis of the major degradation products of this peptide revealed that the critical peptide bond cleaved was Cys105-Phe106. We conclude that the Cys-Phe peptide bond renders atrial peptides highly susceptible to proteolysis by renal brush border membranes, resulting in inactivation.

Inactivation of atrial natriuretic factor by the renal brush border

Atrial natriuretic factor (ANF), a 28-amino-acid peptide secreted from the mammalian heart, is known to be cleared rapidly from the circulation. In vitro and in vivo studies implicate the kidney as an important site for clearance and subsequent degradation of atrial natriuretic factor. We have observed that atrial natriuretic factor is inactivated rapidly by rabbit kidney brush-border membranes. The rate of degradation of ANF measured by the loss of bioactivity followed a similar time-course to the decrease in peptide peak area measured by high-performance liquid chromatography. Interestingly, inactivation of ANF produced only a single major degradation product, which was isolated and purified. Sequence analysis revealed that the product had the same sequence of amino acids as ANF with the Cys-7-Phe-8 bond cleaved and the disulfide bridge between Cys-7 and Cys-23 remaining intact. As the renal brush border contains an abundance of proteolytic activities, it is surprising that this peptide is cleaved primarily at a single peptide bond.

Uptake of aminoglycoside antibiotics into brush-border membrane vesicles and inhibition of (Na+ + K+)-ATPase activity of basolateral membrane

The effects of aminoglycoside antibiotics on plasma membranes were studied using rat renal basolateral and brush-border membrane vesicles. 3',4'-Dideoxykanamycin was bound to the basolateral membrane and brush-border membrane vesicles. They had a single class of binding sites with nearly the same constant, and the basolateral membrane vesicles had more binding sites than those of the brush-border membrane. Dideoxykanamycin B was transported into the intravesicular space of brush-border membrane vesicles, but not into that of basolateral membrane vesicles. The (Na+ + K+)-ATPase activity of the plasma membrane fraction prepared from the kidney of rat administered with dideoxykanamycin B intravenously decreased significantly. Aminoglycoside antibiotics entrapped in the basolateral membrane vesicles inhibited (Na+ + K+)-ATPase activity, but those added to the basolateral membrane vesicles externally failed to do so. The activity of (Na+ + K+)-ATPase was non-competitively inhibited by gentamicin. It is thus concluded that aminoglycoside antibiotics are taken up into the renal proximal tubular cells across the brush-border membrane and inhibit the (Na+ + K+)-ATPase activity of basolateral membrane. This inhibition may possibly disrupt the balance of cellular electrolytes, leading to a cellular dysfunction, and consequently to the development of aminoglycoside antibiotics' nephrotoxicity.

Specific binding of atrial natriuretic polypeptide to renal basolateral membranes in spontaneously hypertensive rats (SHR) and stroke-prone SHR

The binding of alpha-human atrial natriuretic polypeptide (alpha-hANP) to basolateral membranes isolated from renal cortex of spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHR-SP) was measured at 0 degree C and compared with that of Wistar-Kyoto rats (WKY). The binding of 125I-alpha-hANP in SHR and SHR-SP at 14-15 weeks old demonstrated different binding profiles compared with that in WKY, though there were no apparent differences of the profiles among WKY, SHR and SHR-SP at 5 weeks old. For the high affinity binding sites, the apparent dissociation constant and the maximal binding capacity in SHR and SHR-SP were significantly decreased in comparison with those in WKY. The present data suggest that the altered characteristics of specific receptors for atrial natriuretic polypeptide in SHR and SHR-SP may be involved in the development or maintenance of genetic hypertension.

H+ gradient-dependent transport of aminocephalosporins in rat intestinal brush-border membrane vesicles. Role of dipeptide transport system

The transport of cephalosporin antibiotics in brush-border membrane vesicles isolated from rat small intestine has been studied by a rapid filtration technique, demonstrating a carrier-mediated transport system for aminocephalosporins such as cephradine. In agreement with the transport mechanisms of dipeptides, the uptake of cephradine by brush-border membrane vesicles was Na+-independent and was stimulated in the presence of an inward H+ gradient ([H+]o greater than [H+]i). Cephradine uptake in the presence of an inward H+ gradient was a saturable process with an apparent Km of 9.4 mM, and was markedly inhibited by dipeptides but not inhibited by amino acids. The present data suggest that aminocephalosporins can be transported by a common carrier-mediated system with dipeptides in the intestinal brush-border membranes and this process may be driven by an H+ gradient.

Role of chloride on carrier-mediated transport of p-aminohippurate in rat renal basolateral membrane vesicles

Effect of inorganic anions on p-amino[3H]hippurate transport in renal basolateral membranes has been studied using the vesicles preloaded with unlabeled p-aminohippurate (countertransport condition). The uptake of p-amino[3H]hippurate was stimulated by the outward gradient of unlabeled p-aminohippurate and the labeled substrate was accumulated into the vesicles against its concentration gradient in the presence of Cl-. The substitution of SCN- and SO4(2-) for Cl- in both sides of the vesicles depressed the initial rate and the overshoot magnitude of p-amino[3H]hippurate uptake. These results suggest that Cl- may play an important role for the carrier-mediated transport system of organic anion in renal basolateral membranes.

Distinction of three types of D-glucose transport systems in animal cells

Immunoblotting of plasma membrane fractions from rat kidney cortex with antibody to human erythrocyte glucose transporter showed a single major cross-reacting material of 48K in basolateral membrane fractions possessing a facilitated diffusion system for D-glucose, but not in brush border membrane fractions which have a Na-dependent active transport system. Cytochalasin B inhibited D-glucose uptake in basolateral membrane vesicles but not in brush border vesicles. Cross-reacting materials of 44-55K were detected in several animal cells exhibiting facilitated diffusion systems, including a hormone dependent system. These results indicate molecular difference between glucose transporters of facilitated diffusion systems and active transport systems.

Cimetidine transport in rat renal brush border and basolateral membrane vesicles

The transport of cimetidine by rat renal brush border and basolateral membrane vesicles has been studied in relation to the transport system of organic cation. Cimetidine inhibited [3H]tetraethylammonium uptake by basolateral membrane vesicles in a dose dependent manner, and the degree of the inhibition was almost the same as that by unlabeled tetraethylammonium. In contrast, cimetidine inhibited the active transport of [3H]tetraethylammonium by brush border membrane vesicles more strongly than unlabeled tetraethylammonium did. In agreement with the transport mechanism of tetraethylammonium in brush border membranes, the presence of an H+ gradient ([H+]i greater than [H+]o) induced a marked stimulation of cimetidine uptake against its concentration gradient (overshoot phenomenon), and this concentrative uptake was inhibited by unlabeled tetraethylammonium. These results suggest that cimetidine can share common carrier transport systems with tetraethylammonium in renal brush border and basolateral membranes, and that cimetidine transport across brush border membranes is driven by an H+ gradient via an H+-organic cation antiport system.

Specific receptors for atrial natriuretic polypeptide on basolateral membranes isolated from rat renal cortex

The binding of alpha-human atrial natriuretic polypeptide (alpha-hANP) to brush border and basolateral membranes isolated from the rat renal cortex was studied at 0 degree C by a rapid filtration technique. Specific binding of 125I-alpha-hANP to basolateral membranes reached a steady state at 4 hr. The binding to brush border membranes was maximal at 5-15 min and then rapidly decreased. The analysis of incubation mixtures with basolateral membranes revealed little degradation of 125I-alpha-hANP during the 4-hr incubation, while there was extensive degradation of the ligand with brush border membranes during the 30-min incubation. High affinity binding of 125I-alpha-hANP was demonstrated on basolateral membranes but not on brush border membranes. These data suggest that specific receptors for alpha-hANP are localized on basolateral membranes of the renal cortex.

The basolateral membrane of rat enterocyte: its purification from brush border contamination

Basolateral membranes obtained by self-orienting Percoll-gradient centrifugation were treated with 5 mM CaCl2 to minimize the cross-contamination by brush border membranes. From marker enzyme-specific activities it was calculated that in this preparation the basolateral/brush border membrane ratio was 22.6. A low L-glucose permeability across basolateral membrane vesicles together with ATP-dependent sodium uptake was observed.

Na+-dependent transport of alpha-aminoisobutyrate in isolated basolateral membrane vesicles from rat parotid glands

Basolateral plasma membranes were prepared from rat parotid gland after centrifugation in a self-orienting Percoll gradient. K+-dependent phosphatase [Na+ + K+)-ATPase), a marker enzyme for basolateral membranes, was enriched 10-fold from tissue homogenates. Using this preparation, the transport of alpha-aminoisobutyrate was studied. The uptake of alpha-aminoisobutyrate was Na+-dependent, osmotically sensitive, and temperature-dependent. In the presence of a Na+ gradient between the extra- and intravesicular solutions, vesicles showed an 'overshoot' accumulation of alpha-aminoisobutyrate. Sodium-dependent alpha-aminoisobutyrate uptake was saturable, exhibiting an apparent Km of 1.28 +/- 0.35 mM and Vmax of 780 +/- 170 pmol/min per mg protein. alpha-Aminoisobutyrate transport was inhibited considerably by monensin, but incubating with ouabain was without effect. These results suggest that basolateral membrane vesicles, which possess an active amino acid transport system (system A), can be prepared from the rat parotid gland.

Effects of trypsin and protein modification on the renal transporter ofp-aminohippurate

Basal-lateral membranous vesicles prepared from rabbit renal cortex exhibited Mg2+-stimulated, probenecid-inhibitable transport of p-aminohippurate (PAH). This uptake could be completely eliminated by incubating the membranes with trypsin at a weight ratio of 1:700 (trypsin/membrane protein). The loss of PAH uptake activity occurred in two stages. Over the first ten minutes of the vesicles' exposure to trypsin, there was a nearly linear loss, with respect to time, of about 80% of the PAH uptake activity. The remaining 20% of activity was resistant to further trypsin digestion for the next ten minutes, but by twenty-five minutes a total inactivation of the uptake activity occurred. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of normal and trypsin-treated vesicles showed very little degradation of proteins. However, two minor polypeptides (Mr - 410,000 and 388,000) were degraded during the first ten minutes of the membranes' exposure to trypsin. After twenty minutes of exposure, two other polypeptides (Mr = 94,500 and 87,500) were degraded. Chymotrypsin and clostripain also caused a loss of PAH transport activity. However, compared to the effects of trypsin, the effects of these two proteases were less complete, slower in onset, and for clostripain, a much higher concentration of enzyme was required. Other functions or properties of the vesicles including morphological appearance, degree of vesiculation, glucose space or Na+-dependent L-glutamate transport and Na+,K+-ATPase activity were not altered by the concentration of trypsin which abolished 80% of the transport of PAH. Thus, it is possible that one or more of the degraded polypeptides detected by polyacrylamide gel electrophoresis comprises the PAH transporter.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical and morphological characterization of a plasma membrane-enriched fraction from bovine parathyroid cells

A fraction of enriched plasma membranes from bovine parathyroid cells has been prepared by differential centrifugation. Biochemical characterization shows that this fraction has a specific activity enrichment of 7.2-fold in ouabain-sensitive Na+-K+ ATPase, and 3.5-fold in 5'-nucleotidase. Less than 4% of the total mitochondria and lysosomes are present within the plasma membranes, while microsomal contamination accounts for 14% of total specific activity. Parathyroid hormone radioimmunoassay also reveals the presence of some secretory granules within the plasma membrane fraction. The characteristic morphological aspect of the unusual surface membrane is shown by freeze-fracture electron microscopy. In the enriched pellets, vesicles identified as having a plasma membrane origin have variable sizes, and 50% show an inside-out conformation. Even though the plasma membrane fraction described herein is not absolutely free from contamination by other subcellular components, this protocol represents the first attempt to purify surface membrane from parathyroid tissue and provide the starting material for understanding, at a molecular level, the properties of extracellular Ca2+ regulation and its coupling with secretion of parathyroid hormone.

Carrier-mediated transport systems of tetraethylammonium in rat renal brush-border and basolateral membrane vesicles

Transport of [3H]tetraethylammonium, an organic cation, has been studied in brush-border and basolateral membrane vesicles isolated from rat kidney cortex. Some characteristics of carrier-mediated transport for tetraethylammonium were demonstrated in brush-border and basolateral membrane vesicles; the uptake was saturable, was stimulated by the countertransport effect, and showed discontinuity in an Arrhenius plot. In brush-border membrane vesicles, the presence of an H+ gradient ( [H+]i greater than [H+]o) induced a marked stimulation of tetraethylammonium uptake against its concentration gradient (overshoot phenomenon), and this concentrative uptake was completely inhibited by HgCl2. In contrast, the uptake of tetraethylammonium by basolateral membrane vesicles was unaffected by an H+ gradient. Tetraethylammonium uptake by basolateral membrane vesicles was significantly stimulated by a valinomycin-induced inside-negative membrane potential, while no effect of membrane potential was observed in brush-border membrane vesicles. These results suggest that tetraethylammonium transport across brush-border membranes is driven by an H+ gradient via an electroneutral H+-tetraethylammonium antiport system, and that tetraethylammonium is transported across basolateral membranes via a carrier-mediated system and this process is stimulated by an inside-negative membrane potential.

Evidence against parallel operation of sodium/calcium antiport and ATP-driven calcium transport in plasma membrane vesicles from kidney tubule cells

The present study aimed to clarify the existence of a Na+/Ca2+ antiport device in kidney tubular epithelial cells discussed in the literature to represent the predominant mechanistic device for Ca2+ reabsorption in the kidney. Inside-out oriented plasma membrane vesicles from tubular epithelial cells of guinea-pig kidney showed an ATP-driven Ca2+ transport machinery similar to that known to reside in the plasma membrane of numerous cell types. It was not affected by digitalis compounds which otherwise are well-documented inhibitors of Ca2+ reabsorption. The vesicle preparation contained high, digitalis-sensitive (Na+ + K+)-ATPase activities indicating its origin from the basolateral portion of plasma membrane. The operation of a Na+/Ca2+ antiport device was excluded by the findings that steep Ca2+ gradients formed by ATP-dependent Ca2+ accumulation in the vesicles were not discharged by extravesicular Na+, and did not drive 45Ca2+ uptake into the vesicles via a Ca2+-45Ca2+ exchange. The ATP-dependent Ca2+ uptake into the vesicles became increasingly depressed with time by extravesicular Na+. This was not due to an impairment of the Ca2+ pump itself, but caused by Na+/Ca2+ competition for binding sites on the intravesicular membrane surface shown to be important for high Ca2+ accumulation in the vesicles. Earlier observations on Na+-induced release of Ca2+ from vesicles pre-equilibrated with Ca2+, seemingly favoring the existence of a Na+/Ca2+ antiporter in the basolateral plasma membrane, were likewise explained by the occurrence of Na+/Ca2+ competition for binding sites. The weight of our findings disfavors the transcellular pathway of Ca2+ reabsorption through tubule epithelium essentially depending on the operation of a Na+/Ca2+ antiport device.

Isopycnic centrifugation of rat-liver microsomes in isoosmotic gradients of Percoll and release of microsomal material by low concentrations of sodium deoxycholate

Rat-liver microsomes were subjected to isopycnic centrifugation under isoosmotic conditions in gradients of Percoll containing 0%, 0.05%, 0.1% and 0.2% sodium deoxycholate, respectively. The buoyant density of the microsomes was in the range 1.043 to 1.046 g/ml, independent of the detergent concentration. Absorbance measurements and polyacrylamide gel electrophoresis revealed that the detergent causes an increase in the release of material from the microsomes. Electron microscopy studies showed that membrane disassembly was avoided if the microsomes were isolated at concentrations below 0.1% sodium deoxycholate.

Kinetic properties of the ATP-dependent Ca2+ pump and the Na+/Ca2+ exchange system in basolateral membranes from rat kidney cortex

Basolateral plasma membranes from rat kidney cortex have been purified 40-fold by a combination of differential centrifugation, centrifugation in a discontinuous sucrose gradient followed by centrifugation in 8% percoll. The ratio of leaky membrane vesicles (L) versus right-side-out (RO) and inside-out (IO) resealed vesicles appeared to be L:RO:IO = 4:3:1. High-affinity Ca2+-ATPase, ATP-dependent Ca2+ transport and Na+/Ca2+ exchange have been studied with special emphasis on the relative transport capacities of the two Ca2+ transport systems. The kinetic parameters of Ca2+-ATPase activity in digitonin-treated membranes are: Km = 0.11 microM Ca2+ and Vmax = 81 +/- 4 nmol Pi/min X mg protein at 37 degrees C. ATP-dependent Ca2+ transport amounts to 4.3 +/- 0.2 and 7.4 +/- 0.3 nmol Ca2+/min X mg protein at 25 and 37 degrees C, respectively, with an affinity for Ca2+ of 0.13 and 0.07 microM at 25 and 37 degrees C. After correction for the percentage of IO-resealed vesicles involved in ATP-dependent Ca2+ transport, a stoichiometry of 0.7 mol Ca2+ transported per mol ATP is found for the Ca2+-ATPase. In the presence of 75 mM Na+ in the incubation medium ATP-dependent Ca2+ uptake is inhibited 22%. When Na+ is present at 5 mM an extra Ca2+ accumulation is observed which amounts to 15% of the ATP-dependent Ca2+ transport rate. This extra Ca2+ accumulation induced by low Na+ is fully inhibited by preincubation of the vesicles with 1 mM ouabain, which indicates that (Na+-K+)-ATPase generates a Na+ gradient favorable for Ca2+ accumulation via the Na+/Ca2+ exchanger. In the absence of ATP, a Na+ gradient-dependent Ca2+ uptake is measured which rate amounts to 5% of the ATP-dependent Ca2+ transport capacity. The Na+ gradient-dependent Ca2+ uptake is abolished by the ionophore monensin but not influenced by the presence of valinomycin. The affinity of the Na+/Ca2+ exchange system for Ca2+ is between 0.1 and 0.2 microM Ca2+, in the presence as well as in the absence of ATP. This affinity is surprisingly close to the affinity measured for the ATP-dependent Ca2+ pump. Based on these observations it is concluded that in isolated basolateral membranes from rat kidney cortex the Ca2+-ATPase system exceeds the capacity of the Na+/Ca2+ exchanger four- to fivefold and it is therefore unlikely that the latter system plays a primary role in the Ca2+ homeostasis of rat kidney cortex cells.