Plasma membranes of mammalian cells: a review of methods for their characterization and isolation

Interaction of anionic Fe3O4 nanoparticles with lipid vesicles: a review on deformation and poration under various conditions

This review focuses on the deformation and poration of lipid vesicles caused by the interaction of anionic magnetite nanoparticles (MNPs). Effects of various factors, such as surface charge density, salt and sugar concentrations in buffer, membrane cholesterol content, polymer-grafted phospholipid, and membrane potential have been discussed for the interaction of MNPs with lipid vesicles. To quantify these effects on the vesicles, compactness, fraction of deformation and poration, dynamics of membrane permeation, and kinetics of membrane permeation have been critically evaluated. The review explores the potential advancements as well as future directions of the research field in the biomedical application of MNPs.

Effects of cholesterol on the anionic magnetite nanoparticle-induced deformation and poration of giant lipid vesicles

We have investigated the effects of cholesterol on the deformation and poration of giant unilamellar vesicles (GUVs) induced by anionic magnetite nanoparticles (NPs). Negatively charged lipid, neutral lipid, and cholesterol were used to prepare the charged GUVs (surface charge density of membranes - 0.16 C m-2), while only neutral lipid and cholesterol were used to prepare the neutral GUVs. Cholesterol content varied from 0 to 40 mole% for preparing the biologically relevant membranes. The degree of deformation has been characterized by compactness, the value of which remains at 1.0 for spherical GUVs. The value of compactness increases with time for both membranes, but this increase depends on cholesterol content. The average compactness decreases with cholesterol content, and at 60 min, the values are 1.280 ± 0.002 and 1.131 ± 0.010 for 0 and 40 mole% cholesterol containing charged GUVs. The average compactness is relatively lower for neutral GUVs for the corresponding cholesterol. Membrane poration has been investigated by the leakage of calcein, which indicates a two-state transition model. The fraction of deformation is higher for charged GUVs than for neutral ones, while the fraction of poration shows the opposite result. Both the fractions decrease with cholesterol content.

Effects of cholesterol on the size distribution and bending modulus of lipid vesicles

The influence of cholesterol fraction in the membranes of giant unilamellar vesicles (GUVs) on their size distributions and bending moduli has been investigated. The membranes of GUVs were synthesized by a mixture of two elements: electrically neutral lipid 1, 2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and cholesterol and also a mixture of three elements: electrically charged lipid 1,2-dioleoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (DOPG), DOPC and cholesterol. The size distributions of GUVs have been presented by a set of histograms. The classical lognormal distribution is well fitted to the histograms, from where the average size of vesicle is obtained. The increase of cholesterol content in the membranes of GUVs increases the average size of vesicles in the population. Using the framework of Helmholtz free energy of the system, the theory developed by us is extended to explain the experimental results. The theory determines the influence of cholesterol on the bending modulus of membranes from the fitting of the proper histograms. The increase of cholesterol in GUVs increases both the average size of vesicles in population and the bending modulus of membranes.

A tumor acidity-driven transformable polymeric nanoassembly with deep tumor penetration and membrane-anchoring capability for targeted photodynamic therapy

In recent years, directly damaging cell membrane therapeutic modalities have attracted great attention in the field of cancer therapy due to their critical role in guaranteeing essential cellular function. In this study, the transformable nanoassembly PEG-Ce6@PAEMA, consisting of the photosensitizer polyethylene glycol-chlorin-e6 (PEG-Ce6) and tumor pH-sensitive polymer poly(2-azepane ethyl methacrylate) (PAEMA), was developed for highly efficient membrane-targeted photodynamic therapy. The PAEMA core is rapidly protonated at the acidic tumor pH, resulting in the disassembly of PEG-Ce6@PAEMA and regeneration of PEG-Ce6. Subsequently, the resultant PEG-Ce6 with a very small size (~2.6 kDa) ensures deep penetration into tumor tissue and direct and rapid anchoring to the cancer cell membrane, eventually achieving superior tumor growth inhibition under light irradiation. Thus, this tumor acidity-driven transformable polymeric nanoassembly provides a simple but efficient strategy for membrane targeting cancer therapy.

Organelle-Targeted Photosensitizers for Precision Photodynamic Therapy

Subcellular organelles are the cornerstones of cells, and destroying them will cause cell dysfunction and even death. Therefore, realizing precise organelle targeting of photosensitizers (PSs) can help reduce PS dosage, minimize side effects, avoid drug resistance, and enhance therapeutic efficacy in photodynamic therapy (PDT). Organelle-targeted PSs provide a new paradigm for the construction of the next generation of PSs and may provide implementable strategies for future precision medicine. In this Review, the recent targeting strategies of different organelles and the corresponding design principles of molecular and nanostructured PSs are summarized and discussed. The current challenges and opportunities in organelle-targeted PDT are also presented.

Stepped vitrification technique for human ovarian tissue cryopreservation

The advantage of stepped vitrification (SV) is avoiding ice crystal nucleation, while decreasing the toxic effects of high cryoprotectant concentrations. We aimed to test this method for human ovarian tissue cryopreservation. Ovarian cortex was taken from 7 fertile adult women. Samples were subjected to an SV protocol performed in an automatic freezer, which allowed sample transfer to ever higher concentrations of dimethyl sulfoxide (DMSO) as the temperature was reduced. Histological evaluation of the vitrified-warmed tissue showed large numbers of degenerated follicles after 24 hours of in vitro culture. We therefore evaluated DMSO perfusion rates by X-ray computed tomography, ice crystal formation by freeze-substitution, and cell toxicity by transmission electron microscopy, seeking possible reasons why follicles degenerated. Although cryoprotectant perfusion was considered normal and no ice crystals were formed in the tissue, ultrastructural analysis detected typical signs of DMSO toxicity, such as mitochondria degeneration, alterations in chromatin condensation, cell vacuolization and extracellular matrix swelling in both stromal and follicular cells. The findings indicated that the method failed to preserve follicles due to the high concentrations of DMSO used. However, adaptations can be made to avoid toxicity to follicles caused by elevated levels of cryoprotectants.

There Is No Simple Model of the Plasma Membrane Organization

Ever since technologies enabled the characterization of eukaryotic plasma membranes, heterogeneities in the distributions of its constituents were observed. Over the years this led to the proposal of various models describing the plasma membrane organization such as lipid shells, picket-and-fences, lipid rafts, or protein islands, as addressed in numerous publications and reviews. Instead of emphasizing on one model we in this review give a brief overview over current models and highlight how current experimental work in one or the other way do not support the existence of a single overarching model. Instead, we highlight the vast variety of membrane properties and components, their influences and impacts. We believe that highlighting such controversial discoveries will stimulate unbiased research on plasma membrane organization and functionality, leading to a better understanding of this essential cellular structure.

Searching Missing Proteins Based on the Optimization of Membrane Protein Enrichment and Digestion Process

A membrane protein enrichment method composed of ultracentrifugation and detergent-based extraction was first developed based on MCF7 cell line. Then, in-solution digestion with detergents and eFASP (enhanced filter-aided sample preparation) with detergents were compared with the time-consuming in-gel digestion method. Among the in-solution digestion strategies, the eFASP combined with RapiGest identified 1125 membrane proteins. Similarly, the eFASP combined with sodium deoxycholate identified 1069 membrane proteins; however, the in-gel digestion characterized 1091 membrane proteins. Totally, with the five digestion methods, 1390 membrane proteins were identified with ≥1 unique peptides, among which 1345 membrane proteins contain unique peptides ≥2. This is the biggest membrane protein data set for MCF7 cell line and even breast cancer tissue samples. Interestingly, we identified 13 unique peptides belonging to 8 missing proteins (MPs). Finally, eight unique peptides were validated by synthesized peptides. Two proteins were confirmed as MPs, and another two proteins were candidate detections.

CrATP interferes in the promastigote-macrophage interaction in Leishmania amazonensis infection

Recent have shown the relationship between Ecto-Nucleoside-Triphosphate-Diphosphohydrolases (Ecto-NTPDases or ecto-nucleotidases) and virulence and infectivity in trypanosomatids. In this work, the inhibition of the ecto-ATPase activities and promastigote growth of Leishmania amazonensis by CrATP was characterized. Furthermore, this compound was used to investigate the role of ecto-nucleotidase in the interaction of L. amazonensis with resident peritoneal macrophages obtained from BALB/c mice. CrATP partially inhibits the ecto-ATPase activity, presenting Ki values of 575·7±199·1 and 383·5±79·0 μm, in the presence or absence of 5 mm MgCl2, respectively. The apparent Kms for ATP (2·9±0·5 mm to Mg2+-dependent ecto-ATPase and 0·4±0·2 mm to Mg2+-independent ecto-ATPase activities) are not significantly altered by CrATP, suggesting a reversible non-competitive inhibition of both enzymes. When CrATP was added to the cultivation medium at 500 μm, it drastically inhibited the cellular growth. The interaction of promastigote forms of L. amazonensis with BALB/c peritoneal macrophages is strongly affected by CrATP. When the parasites were treated with 500 μm CrATP before interacting with macrophages, the adhesion and endocytic indices were strongly reduced to 53·0±14·8% and 39·8±1·1%, respectively. These results indicate that ecto-nucleotidase plays an important role in the infection process caused by Leishmania amazonensis.

An adhesion-based method for plasma membrane isolation: evaluating cholesterol extraction from cells and their membranes

A method to isolate large quantities of directly accessible plasma membrane from attached cells is presented. The method is based on the adhesion of cells to an adsorbed layer of polylysine on glass plates, followed by hypotonic lysis with ice-cold distilled water and subsequent washing steps. Optimal conditions for coating glass plates and time for cell attachment were established. No additional chemical or mechanical treatments were used. Contamination of the isolated plasma membrane by cell organelles was less than 5%. The method uses inexpensive, commercially available polylysine and reusable glass plates. Plasma membrane preparations can be made in 15 min. Using this method, we determined that methyl-beta-cyclodextrin differentially extracts cholesterol from fibroblast cells and their plasma membranes and that these differences are temperature dependent. Determination of the cholesterol/phospholipid ratio from intact cells does not reflect methyl-beta-cyclodextrin plasma membrane extraction properties.

CrATP as a new inhibitor of ecto-ATPases of trypanosomatids

Trypanosomatid protozoa include heteroxenic species some of them pathogenic for men, animals and plants. Parasite membrane contains ecto-enzymes whose active sites face the external medium rather than the cytoplasm. Herpetomonas sp. displayed a Mg2+-dependent ecto-ATPase activity, a Mg-independent ecto-ADPase and an ecto-phosphatase activity. Both, the ecto-ADPase and phosphatase activities were insensitive to CrATP (chromium(III) adenosine 5'-triphosphate complex). Ecto-ATPase activity was reversibly inhibited. At 2 mm ATP the apparent Ki was 4 x 7+/-1 x 0 microm but a fraction of about 40-50% was insensitive to CrATP. Remarkably, at low substrate concentration (0 x 2 mm) more than 90% of the ecto-ATPase was inhibited with Ki=0 x 33+/-0 x 10 microm. These parameter dependences are interpreted as the presence of 2 ecto-ATPases activities, one of them with high ATP apparent affinity and sensitivity to CrATP. DIDS (4,4 diisothiocyanatostilbene 2,2' disulfonic acid), suramin and ADP were also effective as inhibitors. Only ADP presented no additive inhibition with CrATP. The pattern of partial inhibition by CrATP was also observed for the ecto-ATPase activities of Leishmania amazonensis, Trypanosoma cruzi and Trypanosoma rangeli. CrATP emerges as a new inhibitor of ecto-ATPases and as a tool for a better understanding of properties and role of ecto-ATPases in the biology of parasites.

Abundance, complexation, and trafficking of Wnt/beta-catenin signaling elements in response to Wnt3a

BACKGROUND

Wnt3a regulates a canonical signaling pathway in early development that controls the nuclear accumulation of beta-catenin and its activation of Lef/Tcf-sensitive transcription of developmentally important genes.

RESULTS

Using totipotent mouse F9 teratocarcinoma cells expressing Frizzled-1 and biochemical analyses, we detail the influence of Wnt3a stimulation on the expression, complexation, and subcellular trafficking of key signaling elements of the canonical pathway, i.e., Dishevelled-2, Axin, glycogen synthase kinase-3beta, and beta-catenin. Cellular content of beta-catenin and Axin, and phospho-glycogen synthase kinase-3beta, but not Dishevelled-2, increases in response to Wnt3a. Subcellular localization of Axin in the absence of Wnt3a is symmetric, found evenly distributed among plasma membrane-, cytosol-, and nuclear-enriched fractions. Dishevelled-2, in contrast, is found predominately in the cytosol, whereas beta-catenin is localized to the plasma membrane-enriched fraction. Wnt3a stimulates trafficking of Dishevelled-2, Axin, and glycogen synthase kinase-3beta initially to the plasma membrane, later to the nucleus. Bioluminescence resonance energy transfer measurements reveal that complexes of Axin with Dishevelled-2, with glycogen synthase kinase-3beta, and with beta-catenin are demonstrable and they remain relatively stable in response to Wnt3a stimulation, although trafficking has occurred. Mammalian Dishevelled-1 and Dishevelled-2 display similar patterns of trafficking in response to Wnt3a, whereas that of Dishevelled-3 differs from the other two.

CONCLUSION

This study provides a detailed biochemical analysis of signaling elements key to Wnt3a regulation of the canonical pathway. We quantify, for the first time, the Wnt-dependent regulation of cellular abundance and intracellular trafficking of these signaling molecules. In contrast, we observe little effect of Wnt3a stimulation on the level of protein-protein interactions among these constituents of Axin-based complexes themselves.

Preparation of secretory vesicle-free plasma membranes by isopycnic sucrose gradient fractionation of neutrophils purified by the gelatin method

Isolated human neutrophils serve as a model for the in vitro study of host defensive processes as well as the cell biology and biochemistry of primary human cells. We demonstrate that the requirements of the gelatinbased procedure for neutrophil isolation from whole blood induces the complete loss of secretory vesicles from in vitro isolated populations, whereas isolation by a dextran-based methodology results in the preservation of this organelle. Following density fractionation of cellular cavitates, examination of commonly employed plasma membrane marker activities yielded subcellular localization patterns that were indistinguishable between dextran- or gelatin-isolated populations, indicating both populations to be otherwise comparable in terms of the relative complexity and large-scale organization of plasma membranes. Given that the cell surface upregulation of secretory vesicles is implicated as an initial requirement of neutrophil activation as well as an intrinsic feature of neutrophil priming, we show that dextran and gelatin-isolated neutrophils may be considered to occupy functionally nonactivated and primed cellular states, respectively. These differences in phenotype can be exploited in specific ways. We suggest that the gelatin method has technical advantages with regard to the study of neutrophil plasma membranes. In particular, results from this study indicate the gelatin method to be a reliable and effective preparatory technique appropriate for tandem use with density fractionation procedures to achieve rapid isolation of plasma membranes that are uncontaminated by secretory organelles.

The involvement of the plasma membrane in the development of Dictyostelium discoideum. I. Purification of the plasma membrane

A method for the isolation and purification of plasma membranes of Dictyostelium discoideum by equilibrium centrifugation on sucrose followed by Renografin continuous density gradients has been developed and monitored both with electron microscopy and a number of enzyme assays. On electron microscopy, the final plasma membrane fractions are judged to be freethe basis of of nuclei, rough endoplasmic reticulum, lysosomes and peroxisomes. Some profiles of the mitochondrial inner membranes are found within the plasma membrane fractions, but this contamination has been estimated to be only 5%. On the basis on enzyme assays, the plasma membrane fractions contain all the 5'-nucleotidase activity in the final gradients and are free of catalase, acid phosphatase and malate dehydrogenase activity (markers for peroxisomes, lysosomes, soluble enzymes and the matrix of mitochondria). Their content of glucose-6-phosphatase is reduced by more than 70%. The large majority of RNA and DNA have been removed from the preparation.

Alkaline phosphatase is involved in the control of adipogenesis in the murine preadipocyte cell line, 3T3-L1

OBJECTIVE

As alkaline phosphatase may play a role in cell differentiation, our aim was to study the possible role of this enzyme in the differentiation of preadipocytes (3T3-L1 cells) into adipocytes.

RESEARCH METHODS AND PROCEDURES

3T3-L1 cells were grown in medium containing insulin, dexamethasone and IBMX to induce adipogenesis. Adipogenesis was measured using the triglyceride-specific dye, oil red O at 0, 3, 7 and 11 days after initiation of adipogenesis in the presence or absence of the alkaline phosphatase inhibitors, levamisole, histidine and Phe-Gly-Gly. Intracellular localisation of the enzyme was detected using ELF-phosphatase, a fluorescent substrate and alkaline phosphatase gene expression was assessed using RT-PCR.

RESULTS

Alkaline phosphatase activity was detected in untransformed cells (1.91+/-0.62 mU/mg protein) and activity increased 11.5+/-1.4-fold after 11 days treatment with transformation medium and 5.3+/-0.3-fold in transformation medium containing levamisole (p<0.05). Triglyceride content of cells increased 3.1+/-0.2-fold after 11 days treatment with transformation medium and 2.1+/-0.3-fold in the presence of levamisole (p<0.005). Histidine inhibited adipogenesis and alkaline phosphatase to a greater extent than did levamisole, but Phe-Gly-Gly had no effect on these variables. Alkaline phosphatase was localised around the lipid droplets of the cells. Gene expression of alkaline phosphatase increased during adipogenesis.

DISCUSSION

This study demonstrates that tissue-nonspecific alkaline phosphatase is present in 3T3-L1 cells and that it may play a role in the control of adipogenesis.

Phosphatase activity characterization on the surface of intact bloodstream forms of Trypanosoma brucei

Procyclic forms of Trypanosoma brucei possess a phosphatase activity on their external cell surface. This activity, while it dephosphorylates [(32)P]phosphocasein, is inhibited weakly by NaF and tartrate but strongly by vanadate. In this work, we describe the presence of an external phosphatase activity in intact bloodstream forms of T. brucei. With p-nitrophenyl phosphate (pNPP) as substrate, these intact cells produced 3-5 nmol pNP min(-1) mg(-1), linearly for up to at least 30 min. The activity was not significantly increased by Mg(2+), Mn(2+), Ca(2+) and Co(2+), but was inhibited by vanadate, NaF, p-chloromercuribenzoate and Zn(2+) and was insensitive to okadaic acid. Membrane-enriched fractions of parasites contained an acid phosphatase activity, with a pH optimum in the range of 4.5-5.5. This activity hydrolyzed phosphotyrosine (40 nmol phosphate min(-1) mg(-1)) better than phosphothreonine or phosphoserine. Partial purification of this phosphatase yielded a single activity band following gel electrophoresis, a K(m) value of 0.29 mM with pNPP and was insensitive to the Fe(2+)/H(2)O(2)/ascorbate system.

A Mg-dependent ecto-ATPase in Leishmania amazonensis and its possible role in adenosine acquisition and virulence

The plasma membrane of cells contains enzymes whose active sites face the external medium rather than the cytoplasm. The activities of these enzymes, referred to as ectoenzymes, can be measured using living cells. In this work we describe the ability of living promastigotes of Leishmania amazonensis to hydrolyze extracellular ATP. In these intact parasites whose viability was assessed before and after the reactions by motility and by trypan blue dye exclusion, there was a low level of ATP hydrolysis in the absence of any divalent metal (5.39 +/- 0.71 nmol P(i)/h x 10(7) cells). The ATP hydrolysis was stimulated by MgCl(2) and the Mg-dependent ecto-ATPase activity was 30.75 +/- 2.64 nmol P(i)/h x 10(7) cells. The Mg-dependent ecto-ATPase activity was linear with cell density and with time for at least 60 min. The addition of MgCl(2) to extracellular medium increased the ecto-ATPase activity in a dose-dependent manner. At 5 mM ATP, half-maximal stimulation of ATP hydrolysis was obtained with 1.21 mM MgCl(2). This stimulatory activity was also observed when MgCl(2) was replaced by MnCl(2), but not by CaCl(2) or SrCl(2). The apparent K(m) for Mg-ATP(2-) was 0.98 mM and free Mg(2+) did not increase the ecto-ATPase activity. In the pH range from 6.8 to 8.4, in which the cells were viable, the acid phosphatase activity decreased, while the Mg(2+)-dependent ATPase activity increased. This ecto-ATPase activity was insensitive to inhibitors of other ATPase and phosphatase activities, such as oligomycin, sodium azide, bafilomycin A(1), ouabain, furosemide, vanadate, molybdate, sodium fluoride, tartrate, and levamizole. To confirm that this Mg-dependent ATPase was an ecto-ATPase, we used an impermeant inhibitor, 4,4'-diisothiocyanostylbene 2',2'-disulfonic acid as well as suramin, an antagonist of P(2) purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg(2+)-dependent ATPase activity in a dose-dependent manner. A comparison between the Mg(2+)-dependent ATPase activity of virulent and avirulent promastigotes showed that avirulent promastigotes were less efficient than the virulent promastigotes in hydrolyzing ATP.

Ectonucleotide diphosphohydrolase activities in hemocytes of larval Manduca sexta

In this work, we describe the ability of living hemocytes from an insect (Manduca sexta, Lepidoptera) to hydrolyze extracellular ATP. In these intact cells, there was a low level of ATP hydrolysis in the absence of any divalent metal (8.24 +/- 0.94 nmol of Pi/h x 10(6) cells). The ATP hydrolysis was stimulated by MgCl2 and the Mg2+-dependent ecto-ATPase activity was 15.93 +/- 1.74 nmol of Pi/h x 10(6) cells. Both activities were linear with cell density and with time for at least 90 min. The addition of MgCl2 to extracellular medium increased the ecto-ATPase activity in a dose-dependent manner. At 5 mM ATP, half-maximal stimulation of ATP hydrolysis was obtained with 0.33 mM MgCl2. This stimulatory activity was not observed when Ca2+ replaced Mg2+. The apparent Km values for ATP-4 and Mg-ATP2- were 0.059 and 0.097 mM, respectively. The Mg2+-independent ATPase activity was unaffected by pH in the range between 6.6 and 7.4, in which the cells were viable. However, the Mg2+-dependent ATPase activity was enhanced by an increase of pH. These ecto-ATPase activities were insensitive to inhibitors of other ATPase and phosphatase activities, such as oligomycin, sodium azide, bafilomycin A1, ouabain, furosemide, vanadate, sodium fluoride, tartrate, and levamizole. To confirm the observed hydrolytic activities as those of an ecto-ATPase, we used an impermeant inhibitor, DIDS (4,4'-diisothiocyanostilbene-2,2'-disulfonic acid), as well as suramin, an antagonist of P2-purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg2+-independent and the Mg2+-dependent ATPase activities to different extents. Interestingly, lipopolysaccharide, a component of cell walls of gram-negative bacteria that increase hemocyte aggregation and phagocytosis, increased the Mg2+-dependent ecto-ATPase activity in a dose-dependent manner but did not modify the Mg2+-independent ecto-ATPase activity.

Ectonucleotide diphosphohydrolase activities in Entamoeba histolytica

In this work, we describe the ability of living cells of Entamoeba histolytica to hydrolyze extracellular ATP. In these intact parasites, whose viability was determined by motility and by the eosin method, ATP hydrolysis was low in the absence of any divalent metal (78 nmol P(i)/h/10(5) cells). Interestingly, in the presence of 5 mM MgCl(2) an ecto-ATPase activity of 300 nmol P(i)/h/10(5) cells was observed. The addition of MgCl(2) to the extracellular medium increased the ecto-ATPase activity in a dose-dependent manner. At 5 mM ATP, half-maximal stimulation of ATP hydrolysis was obtained with 1.23 mM MgCl(2). Both activities were linear with cell density and with time for at least 1 h. The ecto-ATPase activity was also stimulated by MnCl(2) and CaCl(2) but not by SrCl(2), ZnCl(2), or FeCl(3). In fact, FeCl(3) inhibited both Mg(2+)-dependent and Mg(2+)-independent ecto-ATPase activities. The Mg(2+)-independent ATPase activity was unaffected by pH in the range between 6.4 and 8. 4, in which the cells were viable. However, the Mg(2+)-dependent ATPase activity was enhanced concomitantly with the increase in pH. In order to discard the possibility that the ATP hydrolysis observed was due to phosphatase or 5'-nucleotidase activities, several inhibitors for these enzymes were tested. Sodium orthovanadate, sodium fluoride, levamizole, and ammonium molybdate had no effect on the ATPase activities. In the absence of Mg(2+) (basal activity), the apparent K(m) for ATP(4-) was 0.053 +/- 0.008 mM, whereas at saturating MgCl(2) concentrations, the corresponding apparent K(m) for Mg-ATP(2-) for Mg(2+)-dependent ecto-ATPase activity (difference between total and basal ecto-ATPase activity) was 0.503 mM +/- 0.062. Both ecto-ATPase activities were highly specific for ATP and were also able to hydrolyze ADP less efficiently. To identify the observed hydrolytic activities as those of an ecto-ATPase, we used suramin, a competitive antagonist of P(2) purinoreceptors and an inhibitor of some ecto-ATPases, as well as the impermeant agent 4'-4'-diisothiocyanostylbenzene-2'-2'-disulfonic acid. These two reagents inhibited the Mg(2+)-independent and the Mg(2+)-dependent ATPase activities to different extents, and the inhibition by both agents was prevented by ATP. A comparison among the ecto-ATPase activities of three amoeba species showed that the noninvasive E. histolytica and the free-living E. moshkovskii were less efficient than the pathogenic E. histolytica in hydrolyzing ATP. As E. histolytica is known to have a galactose-specific lectin on its surface, which is related to the pathogenesis of amebiasis, galactose was tested for an effect on ecto-ATPase activities. It stimulated the Mg(2+)-dependent ecto-ATPase but not the Mg(2+)-independent ATPase activity.

Phosphorylation of the complement component, C9, by an ecto-protein kinase of human leukemic cells

Ecto-protein kinases (ecto-PK) are surface constituents of many, if not all, animal cell types; normal, transformed or malignant. The occurrence of ecto-PK on the surface of human leukemia cell lines was described [Paas, Y., Fishelson, Z., 1995. Shedding of tyrosine and serine/threonine ecto-PK from human leukemic cells. Arch. Biochem. Biophys. 316 780-788.]. These ecto-PKs have been shown to phosphorylate several exogenous substrates, including the complement C9 protein, an essential component of the terminal complement system. C9 is phosphorylated by ecto-PK of K562 cells on serine residue(s). Phosphorylation occurs in the N-terminal C9a portion produced by cleavage of phosphorylated C9 with human alpha-thrombin. C9 polymers generated upon incubation of C9 with ZnCl2 do not serve as substrates for the K562 ecto-PK. In contrast, unfolded C9, obtained by reduction and alkylation, serves as a superior substrate for the K562 ecto-PK. Native C9 phosphorylation produced a rather low stoichiometry of incorporated phosphate (around 3%) per C9. Despite that, the phosphorylated C9 expressed reduced hemolytic activity. The complement-sensitive variant of K562 (K562/S) did not express the C9 phosphorylating activity. Various PK inhibitors tested failed to block C9 phosphorylation. Only heparin and 2,3-diphosphoglycerate (dpGA) prevented C9 phosphorylation, indicating that the ecto-PK is related to the casein kinase CK2. C9 can be phosphorylated by ecto-PK from other tumor cells, including Jurkat, SK-OV-3 and BT-474. These results suggest that extracellular phosphorylation of C9 may serve as a protective mechanism against complement in tumor cells.

Ecto-protein tyrosine phosphatase activity in Trypanosoma cruzi infective stages

Live T. cruzi trypomastigotes and amastigotes possess ecto-protein tyrosine phosphatase activity as indicated by the ability of intact cells to catalyze dephosphorylation of tyrosine phosphorylated myelin basic protein, [32P]TyrRaytide, phosphotyrosine, or the phosphotyrosine analog p-nitrophenylphosphate (p-NPP). The dephosphorylation of myelin basic protein (MBP) and p-NPP was inhibited by sodium o-vanadate, zinc chloride and NaF, while dephosphorylation of [32P]TyrRaytide was insensitive to zinc chloride but sensitive to o-vanadate and NaF. In contrast, live cells were not able to dephosphorylate serine or threonine phosphorylated peptides ([32P]Kemptide) or proteins ([32P]RCM-lysozyme and [32P]MBP).

Mg-dependent ecto-ATPase activity in Leishmania tropica

ATPase activity has been located on the external surface of Leishmania tropica. Since Leishmania is known to have an ecto-acid phosphatase, in order to discard the possibility that the ATP hydrolysis observed was due to the acid phosphatase activity, the effect of pH in both activities was examined. In the pH range from 6.8 to 8.4, in which the cells were viable, the phosphatase activity decreased, while the ecto-ATPase activity increased. To confirm that the observed ATP hydrolysis was promoted by neither phosphatase nor 5'-nucleotidase activities, a few inhibitors for these enzymes were tested. Vanadate and NaF strongly inhibited the phosphatase activity; however, no effect was observed on ATPase activity. Neither levamizole nor tetramizole, two specific inhibitors of alkaline phosphatases, inhibited this activity. The lack of response to ammonium molybdate indicated that 5'-nucleotidase did not contribute to the ATP hydrolysis. Also, the lack of inhibition of the ATP hydrolysis by high concentrations of ADP at nonsaturating concentrations of ATP discarded the possibility of any ATP diphosphohydrolase activity. The ATPase here described was stimulated by MgCl2 but not by CaCl2. In the absence of divalent metal, a low level of ATP hydrolysis was observed, and CaCl2 varying from 0.1 to 10 mM did not increase the ATPase activity. At 5 mM ATP, half-maximal stimulation of ATP hydrolysis was obtained with 0.29 +/- 0.02 mM MgCl2. The apparent K(m) for Mg-ATP2- was 0.13 +/- 0.01 mM and free Mg2+ did not increase the ATPase activity. ATP was the best substrate for this enzyme. Other nucleotides such as ITP, CTP, GTP, UTP, and ADP produced lower reaction rates. To confirm that this Mg-dependent ATPase was an ecto-ATPase, an impermeant inhibitor, 4,4'-diisothiocyanostylbene-2,2'-disulfonic acid was used. This amino/sulfhydryl-reactive reagent did inhibit the Mg-ecto-ATPase activity in a dose-dependent manner (I0.5 = 27.5 +/- 1.8 microM).

Oxysterol-induced endothelial cell dysfunction in culture

Cholesterol oxidation products (oxysterols), such as cholestan-3 beta,5 alpha,6 beta-triol (Triol), may be atherogenic by altering the barrier function of the vascular endothelium. We have shown that incubation of endothelial cell monolayers with Triol increased transendothelial albumin transfer (i.e., decreased barrier function) in a concentration- and time-dependent manner. Such dysfunction of endothelium could result from alterations in membrane characteristics, including changes in membrane-associated enzyme activities. To test this hypothesis, endothelial monolayers were treated with 20 microM Triol and the activities of selected membrane enzymes were measured at 0, 2, 4, 6, 12 and 24 hours. Calcium-adenosine triphosphatase (Ca(++)-ATPase) and sodium, potassium, magnesium-adenosine triphosphatase (Na+, K+, Mg(++)-ATPase) activities were significantly increased after 4 or 2 hours incubation with 20 microM Triol, respectively. 5'-nucleotidase activity was significantly elevated only after a 24-hour exposure to Triol, whereas there was no change in angiotensin-converting enzyme (ACE) activity in response to 20 microM Triol treatment at any time studied. Compared with all concentrations tested 40 microM Triol increased Ca(++)-ATPase activity most markedly, with a significant increase already after a 2-hour exposure. No major morphological changes were noted until 12 hours of exposure to 20 microM Triol; obvious cellular damage was observed by 24 hours. Cultures treated with Triol for 24 hours showed significant signs of toxicity, measured by an elevated [3H]adenine release, compared with control cultures. These data demonstrate that Triol alters the activity of certain membrane-bound enzymes, particularly Na+, K+, Mg(++)-ATPase and Ca(++)-ATPase.(ABSTRACT TRUNCATED AT 250 WORDS)

A Na+/H+ exchanger and its relation to oxidative effects in plasma membrane vesicles from lens fibers

The existence of a Na+/H+ exchange mechanism and its role in the regulation of lens fiber cell intracellular pH, as well as the effect of oxidants and antioxidants, have been examined in vesicular preparations from spiny dogfish and bovine eyes. The fluorescent probes, SBFI (sodium-binding benzofuran isophthalate) for Na+ and SNARF-1 (seminaphthorhodafluor-1) for H+, were used to determine fluorescent ratios in a dual-wavelength spectrofluorimeter. The results show that: (1) the plasma membrane vesicles can be purified from lens fiber (52.5% of the vesicles were in the right-side out orientation for the fish eyes and 56.3% for the bovine eyes, show enrichment for the membrane marker activities and have an average size of 0.2-0.5 microns); (2) the influx of Na+ was dependent on an outwardly directed pH gradient with the uptake of Na+ sensitive to 500 microM amiloride but not affected by 50 microM valinomycin and 50 mM K gluconate; (3) when the pHo (extravesicular pH) of the vesicles was set at 8.1 and pHi (intravesicular pH) to 6.1, an inwardly directed Na+ gradient caused an increase in intravesicular pH by about 0.3 pH unit, and in bovine lens fiber vesicles the Na+ influx is highly dependent on the intravesicular pH (or on the pHo/pHi gradient); (4) 50 microM H2O2 increases the Na+/H+ exchange rate by 174% in the vesicles derived from fish lens fibers. Similarly, 100 microM H2O2 stimulates the Na+/H+ exchange rate by 194% in bovine eye fibers. This activation is prevented by preincubation with GSH (reduced glutathione) but not with GSSG (oxidizing glutathione). We conclude that a Na+/H+ exchange mechanism is present in the lens fiber membranes. This exchange possibly regulates intracellular pH and controls the intracellular Na+ concentration. The sensitivity of the Na+/H+ exchanger to the oxidant, hydrogen peroxide (H2O2) and the protection by the antioxidant GSH suggests a possible role for the Na+/H+ exchange mechanism in the formation of cataracts.

Receptor-recycling model of clearance and distribution of insulin in the perfused mouse liver

After perfusion of mouse livers with A14-125I-insulin for designated intervals, an acid-wash technique was employed to separately measure the surface-bound (Xs) and intracellular (Xi) A14-125I-insulin, as well as intracellular degradation products (Xdeg) of labelled insulin. From the perfusate concentrations (Cp) of A14-125I-insulin, the apparent intrinsic hepatic clearance of labelled insulin at a high dose (0.2 nmol/l) was shown to be 60% smaller than that at a low dose (0.018 nmol/l), indicating that the cellular uptake of insulin is remarkably nonlinear at the concentration range examined. From the time courses of Cp, Xs, Xi and Xdeg, the hepatic insulin disposition was shown to be largely accounted for by the receptor-mediated endocytosis. The observed data at the low dose were analysed to estimate biochemical parameters, (i.e., total receptor number, endocytotic rate constant and intracellular degradation rate constant) according to "receptor-recycling" and "non-receptor-recycling" models, using a computer-aided optimization procedure. The "receptor-recycling" model could not only adequately explain the Cp, Xs, Xi and Xdeg at the low dose, but also predict the Cp at the high dose. On the other hand, a "non-receptor-recycling" model, in which recycling of receptors was not assumed, could also explain the observed data at the low dose, but failed to predict the Cp at the high dose, indicating that the receptor recycling process is necessary to explain the hepatic insulin clearance at high insulin concentrations, at which hepatic insulin clearance should be limited by the rate of receptor recycling.(ABSTRACT TRUNCATED AT 250 WORDS)

Human neutrophils produce free radicals from the cell-zymosan interface during phagocytosis and from the whole plasma membrane when stimulated with calcium ionophore A23187

The production of free radicals, superoxide anions (O2-), and hydrogen peroxide (H2O2) was histochemically investigated in human neutrophils that were stimulated by either phagocytosis or the calcium ionophore A23187. To demonstrate O2-, peripheral neutrophils from healthy donors were incubated at 37 degrees C in a medium containing nitroblue tetrazolium and glucose in the presence of either opsonized zymosan A and/or A23187. To demonstrate H2O2, neutrophils pretreated with a stimulant for 10 min were washed and incubated in a cerium medium containing CeCl3 and glucose in a Tris-maleate buffer. In cells engaged in phagocytosis, diformazan (for O2-) and cerium perhydroxide deposits (for H2O2) were restricted to the neutrophil-particle interface and on the inner surface of phagosomes. The remaining free surface of the plasma membrane was devoid of reaction products. In the case of neutrophils stimulated with A23187, the production of O2- and H2O2 was visualized over the whole surface of the plasma membrane. These histochemical reactions were inhibited by p-benzoquinone, superoxide dismutase, ferricytochrome c or catalase, and p-diazobenzenesulfonate (a membrane-impermeable protein denaturant). The results showed that human neutrophils produce free radicals exocellularly and that the site of production varies with different stimuli.

Electrolyte induced vesiculation of MA782 mice mammary adenocarcinoma ascites cells

MA782 ascites cells were found to vesiculate when incubated in electrolyte solutions and release giant plasma membrane vesicles with diameters ranging from 5 microns to 15 microns. The vesicles, generated from the plasma membrane and free of cellular organelles, as visualized by microscopy and marker-enzyme analysis, could be proposed as a useful model membrane system.

Hepatic subcellular localization of cresylbenzodioxaphosphorin oxide (CBDP)-sensitive soman binding sites

The toxicity of the organophosphorus poison soman (pinacolylmethylphosphonofluoridate) is attributable to its irreversible inhibition of the enzyme acetylcholinesterase. In addition, soman binds irreversibly to a number of noncholinesterase tissue binding sites which appear to be its major means of in vivo detoxification. This study was conducted to determine the hepatic subcellular localization of these sites. Subcellular fractions of liver from male Sprague-Dawley rats (200-250 g) were prepared by differential and isopycnic density gradient centrifugation. The binding of [14C]soman to these subcellular fractions was determined in the presence and absence of cresylbenzodioxaphosphorin oxide (CBDP), a compound that binds irreversibly to the noncholinesterase soman binding sites. Crude fractionation of liver homogenates into nuclear, mitochondrial, microsomal, and soluble fractions revealed that 78% of the total CBDP-sensitive binding activity was localized in the nuclear and microsomal fractions. Further purification of these fractions indicated that all of the homogenate binding activity could be accounted for in the purified microsomal fraction. When purified liver microsomes were solubilized and fractionated on linear sucrose gradients, 90% of the CBDP-sensitive soman binding activity cosedimented with carboxylesterase activity which suggests that these binding sites are carboxylesterase.

Membrane fractions display different lipid and enzyme content in three cell types in 16-cell stage embryos of sea urchins

Three cell types were isolated from dissociated 16-cell sea urchin embryos. Four membrane density fractions from discontinuous gradients have different proportions of lipids, surfacer markers and enzymes for the three cell types. Assays of lipid content, CH/PLIPID and SPH/PC ratios, acyl chain length, level of unsaturation by proton NMR and assays of enzyme activity revealed variation at the same density between the three cell types and among different densities from one cell type. There were also differences between whole embryos and dissociated embryo cells. There was no typical membrane domain at a particular density common to the cell types. Cell surface characteristics and polarity of adult cells rely on which lipid domains and enzymes are present, their association with cytoskeleton and how they are localized. At the 16-cell stage these characteristics are still very dynamic as revealed by cytochemical localization of Na+/K(+)-ATPase which varied with cell type and suggests endocytosis at set times in the division cycle. Polarity has not been permanently set for Na+/K(+)-ATPase yet. Membrane enzyme and lipid distributions unique to the three cell types seen in this study suggest parcelling out or insertion of new membrane domains occurs during early sea urchin cleavage. Perturbation of membrane density distribution and lipid content occurs after treatment of embryos with animalizing and vegetalizing teratogens which alter development.

Characterization of a Ca2(+)-ATPase in osteoclast plasma membrane

The plasma membrane fraction of chicken osteoclasts was purified utilizing 20% continuous Percoll gradients. Biochemical marker enzyme analysis (ouabain-sensitive Na+,K(+)-ATPase and 5'-nucleotidase) indicated that plasma membrane enrichment was 11.87-fold and 7.25-fold, respectively, and contamination with mitochondria, endoplasmic reticulum, and lysosomes was low as determined by succinic dehydrogenase, NADH dehydrogenase, and N-acetylglucosaminidase activities, respectively. SDS latency of Na+,K(+)-ATPase and 5'-nucleotidase activities of the isolated plasma membranes revealed that 43-50% of vesicles were sealed, with 10-16% in the inside-out orientation, depending on the membrane fraction used. Electron microscopy confirmed the vesicular nature of the plasma membrane fraction. The plasma membrane Ca2(+)-ATPase had a high-affinity (KCa = 0.22 microM; Vmax = 0.16 mumol/mg per min) and a low-affinity (KCa = 148 microM; Vmax = 0.37 mumol/mg per min) component. Calmodulin (0.12 microM) had no effect on Ca2(+)-ATPase activity. However, trifluoperazine (0.1 mM), a calmodulin antagonist, strongly inhibited especially the high-affinity component of the enzyme. Vanadate and lanthanum also caused inhibition. In the presence of CDTA, a potent Ca2+ and Mg2+ chelating agent, high-affinity Ca2(+)-ATPase activity was abolished, indicating that trace Mg2+ was essential for activity. The Ca2(+)-ATPase substrate curve using ATP showed a high-affinity (Km = 12.3 microM; Vmax = 0.022 mumol/mg per min) and a low-affinity (Km = 43.8 microM; Vmax = 0.278 mumol/mg per min) component. These results demonstrate that osteoclasts have a plasma membrane Ca2(+)-ATPase with characteristics similar to the enzyme responsible for active calcium extrusion in other cells.

Characterization of the incorporation of woodchuck hepatitis virus surface antigen into hepatocyte plasma membrane in woodchuck hepatitis and in the virus-induced hepatocellular carcinoma

Interaction between woodchuck hepatitis virus surface antigen and proteins of hepatocyte plasma membranes were examined in the course of woodchuck hepatitis virus infection. Membranes purified from animals with histologically confirmed acute hepatitis, active or persistent chronic hepatitis and the virus-related hepatocellular carcinoma were evaluated for the virus surface antigen contents, treated with agents eluting plasma membrane-bound antigen to test the extent of the antigen-membrane associations and incubated with purified, particulate woodchuck hepatitis virus surface antigen to determine membrane potential for the antigen adsorption. Hepatocyte plasma membranes originating from woodchucks chronically infected with the virus showed the highest quantities of the incorporated virus surface antigen among membranes studied, the behavior of bound antigen as an integral and a peripheral membrane protein and the resistance to bind an exogenous antigen. Similar properties were expressed by plasma membranes prepared from hepatocytes of nontumor parenchyma displaying chronic active hepatitis of a woodchuck hepatitis virus carrier with hepatoma. Furthermore, plasma membranes originating from animals with active or persistent chronic hepatitis demonstrated identical properties, implicating that histologic activity of the chronic liver inflammatory process is not dependent on the quantity of the virus surface antigen insertion into the membrane. In contrast, hepatocyte plasma membranes from animals with acute hepatitis showed significantly lower antigen quantities, presence of the antigen specificity exclusively behaving as an integral membrane protein and noticeable ability to bind an exogenous surface antigen of the virus. Comparable, but not identical, features were observed for hepatocyte membranes purified from nodules of hepatocellular carcinoma, suggesting that neoplastic transformation of infected hepatocytes is associated with loss of the membrane-bound antigen and with simultaneous, partial recovery of the membrane potential for the antigen binding. Comparative analysis of the properties on the woodchuck hepatitis virus surface antigen incorporation into hepatocyte plasma membranes in studied cases indicated that sustained infection with woodchuck hepatitis virus leads to an increase in the quantity of the membrane-incorporated antigen and to the appearance of the virus surface antigen specificity behaving as a peripheral membrane protein. In conclusion, this study demonstrated that the extent and the character of the antigen interaction with hepatocyte plasma membranes undergoes significant variations in the natural course of hepadna viral infect

Biochemical properties of isolated transverse tubular membranes

This review addresses the major biochemical and structural characteristics of isolated transverse tubule (T-tubule) membranes, including methods of isolation and morphology of purified membranes, evaluation of attendant membrane activities, including ion pumps and channels, and structural and compositional analyses of functionally relevant components. Particular emphasis is placed on the Mg2+-ATPase, its localization in the T-system, its unusual kinetic properties, its possible functions, and its potential regulation by diacylglycerol and other biologically-relevant lipids. Conclusions are drawn with respect to the biochemical markers characteristic of T-tubule membranes and the criteria to be applied in the assessment of isolated T-tubule membrane purity.

Hepatic asialoglycoprotein receptor-mediated binding of human polymeric immunoglobulin A

In the rat, asialoorosomucoid and rat dimeric immunoglobulin A are both taken up by hepatocytes via receptor-mediated endocytosis. The fate of these two proteins, however, differs significantly. Rat dimeric IgA is taken up into smooth vesicles, transported to the bile canaliculus and secreted intact into the bile, whereas asialoglycoproteins are internalized via coated vesicles and transported to lysosomes for degradation. Recently, several studies both in the rat and in cultured human hepatoma cells have suggested that the receptor for asialoglycoproteins may play a role in the hepatic uptake and processing of human polymeric IgA. Using receptor-binding techniques, we have provided quantitative data for the competition of human monomeric, polymeric and secretory IgA with asialoorosomucoid for its receptor on liver plasma membrane preparations from rat, monkey and man. Some IgA molecules required desialylation with neuraminidase to enhance markedly their efficacy for asialoorosomucoid inhibition. Quantitatively, human IgA molecules showed an affinity for the ASOR receptor similar to that for asialoceruloplasmin. Rat dimeric IgA does not compete for this binding site. We conclude that human IgA can compete with ligands for the asialoglycoprotein receptor of rat, monkey and human liver. This receptor may provide an alternative pathway for the hepatic processing of IgA and IgA immune complexes when secretory component-mediated uptake is not available as in the monkey and man, particularly under pathological conditions where serum IgA concentrations accumulate to abnormally high levels.

A beta 1-integrin receptor for fibronectin in human kidney glomeruli

The fibronectin receptor (FNR) is a transmembrane heterodimeric glycoprotein which shares a common beta 1-chain with several other members of the integrin family of adhesion receptors. The authors have prepared a membrane fraction of isolated human glomeruli, from which two proteins (apparent molecular weights 120 kd and 140 kd) bound to a fibronectin-column, and were selectively released by the synthetic peptide Arg-Gly-Asp-Ser. These molecules were labeled in immune overlays by an antibody raised against the FNR from human placenta that recognizes both the FNR-specific a-chain and the group-specific beta 1-integrin chain. In sections of normal human kidneys this antibody labeled predominately the mesangia and the peripheral capillary walls of glomeruli by an immunoperoxidase procedure. Quantitative immunoelectron microscopy, using an indirect immunogold procedure, revealed a preferential localization along the cell membranes of mesangial, epithelial, and endothelial cells that face the mesangial matrix or the glomerular basement membrane (GBM). In kidney biopsies from patients with various glomerular diseases (membranous and other forms of glomerulonephritis, minimal change disease) the distribution was similar to that in normal glomeruli. These findings indicate that a beta 1-integrin-related FNR is present in normal and diseased human glomeruli.

Characterization of the binding sites for glutaraldehyde-polymerized albumin on purified woodchuck hepatocyte plasma membranes

Highly purified woodchuck hepatocyte plasma membranes demonstrated tight specific binding to glutaraldehyde-polymerized serum albumin immobilized on Sepharose macrobeads. This phenomenon was characterized in detail and used for recognition of the plasma membrane constituents involved in binding of the albumin polymer. The hepatocyte membrane-polyalbumin interaction was found to be ligand-specific, saturable, and time-dependent. Other characteristics of a specific receptor-ligand interaction were also noted, including a dependence on the temperature, pH, and ionic strength of the binding medium. Kinetic studies revealed the presence of two classes of binding sites for glutaraldehyde-polymerized albumin on purified membranes. The sites mediating the saturable high-affinity binding of polymer to hepatocyte membranes could not be solubilized by Triton X-100. Binding activity of Triton-insoluble membrane residues was inhibited by heat treatment and proteolysis, and was significantly suppressed by neuroaminidase digestion. These findings suggest a glycoprotein nature for the high-affinity binding sites and indicate that the corresponding receptors apparently are tightly associated with the plasma membrane matrix. In contrast, low-affinity binding of polymeric albumin was inhibited by both Triton X-100 and pronase, was resistant to neuraminidase, and was activated by lipase, suggesting that membrane lipids are important for the binding conduct. In conclusion, these results provide clear evidence that hepatocyte plasma membranes are endowed with at least two classes of chemically distinct binding components, which are able to specifically recognize serum albumin artificially modified by glutaraldehyde treatment. Therefore, they suggest that in vivo hepatocytes may perform a specific receptor-dependent uptake of ligands expressing glutaraldehyde-polymerized albumin specificity. This phenomenon may play an important role in the proposed participation of naturally modified human serum albumin as a bridge in the attachment and penetration into host hepatocyte of hepatitis B virus, which is known to possess a receptor that is specific for glutaraldehyde-cross-linked human serum albumin.

Cerium-induced light-microscopic demonstration of 5'-nucleotidase activity in the lymphatic capillaries of the proximal oesophagus of the rat

Lymphatic capillaries with narrow lumina cannot be identified with certainty by means of conventional light microscopy. This, however, can be achieved with great precision by means of labelling the 5'-nucleotidase activity which is high in lymphatic capillaries. In blood capillaries, on the other hand, it is either lacking or much less pronounced depending on the organ. The reactions performed thus far occurred primarily in the presence of lead ions which had a toxic effect on the enzymes. In cerium, however, this inhibiting influence can be neglected. 2 light-microscopic procedures of labelling the 5'-nucleotidase activity, which make use of cerium, are presented and compared here for the first time. The cerium perhydroxide technique is especially suited for demonstrating the lymphatic capillaries. In comparison to the previous enzyme histochemical methods, a definitely more precise demonstration of the endothelia of small lymphatics now is possible. The reason for this is that this method only reacts to regions of high enzyme activity. As opposed to previous tests on cryostat sections, the lumen of the lymphatic capillary is nearly always identifiable as such if employing this type of reaction. These properties of the cerium-perhydroxide reaction allow definite statements regarding the distribution of the lymphatic capillaries in the tissue. Its simple and rapid course of reaction favour the use of this method in clinical problems. In the other technique presented, the manganese dioxide technique, the demonstration of lymphatic capillaries is by far less exact due to its greater sensitivity even to low enzyme activities.

Improved methods for separating hydrolytic granules of neutrophil leucocytes

Highly efficient methods for isolating two hydrolytic granules of neutrophils are described. Neutrophil obtained from guinea pig peritoneal exudate cells were washed extensively with isotonic sucrose and then treated with heparin. More than 95 per cent of the cells so treated were disrupted with a Dounce homogenizer. Since nuclei were broken, leaving other organelles intact, homogenates were incubated with DNase to reduce viscosity. Postnuclear supernatants were centrifuged on a discontinuous gradient of Percoll. Azurophil granules, high in beta-glucuronidase activity, sedimented at fractions of d = 1.081 and showed very little activity of other marker enzymes. High neutral alpha-glucosidase activity was observed in granular fractions of d = 1.038 and it is suggested that this is a marker for specific granules of neutrophils.

Neutral maltase of human granulocytes: localization on the extracytoplasmic side of the plasma membrane and some properties

Neutral maltase is an alpha-glucosidase (alpha-D-glucoside glucohydrolase, EC 3.2.1.20) which is present in human granulocytes and B-lymphocytes but not in T-lymphocytes. These cells have been reported to contain a renal-type neutral maltase which cross-reacts with an antiserum raised against kidney brush-border enzyme. No study has been performed to assess the subcellular localization of the enzyme. Molecular properties of leukocyte neutral maltase from any species are unknown. We report in this paper that neutral maltase is present on the extracytoplasmic side of human granulocyte plasma membrane. These results are supported by subcellular fractionation on Percoll gradient and by papain digestion of intact granulocytes. The enzyme is probably an integral membrane protein. The anchorage to the lipid bilayer may be similar to that of the stalked brush-border hydrolases. Some properties of granulocyte neutral maltase were also determined on a plasma membrane-enriched fraction. The enzyme cleaves maltose and nigerose but not other glucosides disaccharides and oligosaccharides. The Km for maltose is (+/- SD) 0.78 (+/- 0.06) mM, that for nigerose 21.05 (+/- 1.43) mM. The Vmax for nigerose is 0.83-fold that for maltose. Tris, maltotriose, maltotetraose, and maltopentaose were inhibitors of granulocyte neutral maltase.

Hepatic alpha 1 and beta adrenergic receptors in various animal species

Plasma membranes were isolated from the livers of various animal species representing the four vertebrate classes: Amphibia, Reptilia, Aves and Mammalia. These liver plasma membranes displayed comparable levels of purity as judged by marker enzyme analysis. The activities of the two marker enzymes, 5'-nucleotidase and gamma-glutamyltranspeptidase displayed striking, and quite different, species-dependent differences, with no apparent relationship to phylogeny. alpha 1 and beta-adrenergic receptors were characterized in isolated liver plasma membranes by radioligand binding techniques. The hepatic beta-adrenergic receptor was found to be expressed in all animals studied; the hepatic alpha 1-adrenergic receptor was absent in Amphibia and Reptilia, co-expressed with the beta receptor in Aves, and dominant over the beta receptor in Mammalia. These results suggest that, in liver, the beta-adrenergic receptor is more primitive while the alpha 1-adrenergic receptor is of a more recent phylogenetic origin. It is proposed that the latter may have evolved in conjunction with hepatic sympathetic innervation.

Demonstration of a novel ecto-enzyme on human erythrocytes, capable of degrading ADP and of inhibiting ADP-induced platelet aggregation

The role of ADP as an important inducer of platelet aggregation is generally accepted. Therefore it has been postulated by many authors that the enzymatic removal of extracellular ADP from the circulation is essential to avoid platelet aggregation and thrombus formation. Here we show that erythrocytes essentially contribute to the clearance of ADP. The removal of ADP from suspensions of washed human erythrocytes was due to at least two different activities. One activity, which had already been observed by earlier workers, was identified as adenylate kinase, on the basis of the reaction products and the inhibition by adenosine(5')pentaphospho(5')adenosine (Ap5A). This enzyme was not associated with the cells and was always detectable in cell-free supernatants, indicating that the enzyme had leaked from the cells into the extracellular medium. In contrast, the second activity, which is described here for the first time, was tightly bound to the cells. The activity was not inhibited by Ap5A. The main product of the reaction was AMP, and enzyme activity depended on the presence of divalent cations. The Michaelis constant was about 28 mumol/l. This activity seemed to be an ecto-ADPase. Studies with various inhibitors revealed that degradation of ADP was not due to a non-specific phosphatase. Besides the well known ADPase on the endothelium, the ecto-activity on erythrocytes may play an important part in destroying pro-aggregatory ADP.

Purification and characterization of a Ca2+/Mg2+ ecto-ATPase from rat heart sarcolemma

The Ca2+/Mg2+ ATPase of the rat heart sarcolemmal particles was solubilized with Triton X-100 after treating the membranes with trypsin and purified by high speed centrifugation, ammonium sulfate fractionation, hydrophobic chromatography and gel filtration. The purified enzyme was seen as a single protein band in non-denaturing polyacrylamide gel electrophoresis and its molecular weight by gel filtration was found to be about 240,000. The enzyme utilized Ca-ATP or Mg-ATP as a substrate with high affinity sites (Km = 0.12-0.16 mM) and low affinity sites (Km = 1 mM). The enzyme also utilized CTP, GTP, ITP, UTP and ADP as substrates but at a lower rate in comparison to ATP. The enzyme was activated by Ca2+ (Ka = 0.4 mM) and Mg2+ (Ka = 0.2 mM) as well as by other cations in the order Ca2+ greater than Mg2+ greater than Mn2+ greater than Sr2+ greater than Ba2+ greater than Ni2+ greater than Cu2+. The ATPase activity in the presence of Ca2+ was markedly inhibited by Mg2+, Mn2+, Ni2+ and Cu2+ whereas the monovalent cations such as Na+ and K+ were without effect. The enzyme did not exhibit Ca2+ stimulated Mg2+ dependent ATPase activity and was insensitive to calmodulin, ouabain, verapamil, D-600, oligomycin, azide and vanadate. Optimum pH for Ca2+ or Mg2+ ATPase activity was 8.5-9.0. In view of the possible ectoenzyme nature of the ATPase, its role in adenine nucleotide and Ca2+ metabolism in the myocardium is discussed.