Plasma membrane isolated from astrocytes in primary cultures. Its acceptor oxidoreductase properties

Nitric oxide donors protect cultured rat astrocytes from 1-methyl-4-phenylpyridinium-induced toxicity

MPP+ is thought to mediate MPTP's toxicity on dopamine neurons by inhibiting mitochondrial respiration. However, astrocytic injuries are also observed in MPTP/MPP+-treated rats. Because nitric oxide (NO.) is suggested to be cytoprotective, we examined the effects of nitroprusside (SNP), S-nitroso-N-acetylpenicillamine (SNAP), and 3-morpholinosydnonimine (SIN-1) on MPP+-induced toxicity in astrocytes. Incubation of astrocytes with MPP+ for 2 days produced a dose-dependent toxicity, including increase in lactate level and lipid peroxidation, decrease of metabolic activity and cell damage. SNP, SNAP, and SIN-1 all attenuated MPP+-induced toxicity. The same protection was not achieved with N-acetylpenicillamine or ferrocyanide, structural analogues of SNAP or SNP but devoid of NO.. Further, the effect was not attributed to the increased cGMP levels or blockade of MPP+ accumulation in astrocytes. Notably, catalase, dimethyl sulfoxide and ferricyanide, an extracellular electron acceptor, were also effective in inhibiting MPP+ damage. NO. donors and analogues were also tested against damage produced by rotenone, an irreversible complex I inhibitor. Only ferricyanide and SNP effectively protected rotenone's toxicity. These results concluded that (1) NO. may protect astrocytes from MPP+-induced free radical formation, and (2) prevention of energy depletion/free radicals production alleviate MPP+-induced toxicity.

The plasma membrane NADH-diaphorase is active during selective phases of the cell cycle in mouse neuroblastoma cell line NB41A3. Its relation to cell growth and differentiation

Plasma membrane oxidoreductases have been described in all cells and use extracellular impermeant electron acceptors (DCIP, Ferricyanide) that are reduced by NADH. They appear to regulate the overall cell activity in response to oxidative stress from the cellular environment. An NADH-DCIP reductase has been described at the plasma membrane of NB41A3, a neuroblastoma cell line (Zurbriggen and Dryer (1993) Biochim. Biophys. Acta 1183, 513-520) whose activation with extracellular impermeant substrates promotes cell growth. Elutriation was performed to separate cells and the various fractions were analysed for enzyme activity on intact cells combined with flow cytometry. These studies showed that the enzyme is mostly induced and activated during the G1 and during the G2/M-phases. These observations were further corroborated with specific inhibitors of the cell cycle. A three-fold increase in enzyme activity was observed in the presence of alpha-amanitin, a specific cell cycle inhibitor of the G1-phase. Taxol, a specific inhibitor of the M-phase, also induces a significant increase in enzyme activity. FACS analysis of taxol -treated and alpha-amanitin-treated cells corroborated these data. The cells have been synchronized and the enzyme activity was measured at different time intervals. An activity increase was observed after ca. 2-3 h, that corresponds to a raise in the M-phase, according to FACS data. Furthermore, NTera-2 cells - a human neuroblastoma cell line that differentiates into fully mature neurones in the presence of retinoic acid - exhibit a 50% decrease in the enzyme activity during the G0-phase upon differentiation, compared to undifferentiated cells. Together the data presented in this paper show that this plasma membrane NADH-diaphorase affects cell growth and differentiation and is strongly modulated at various phases of the cell cycle.

Distribution of six transplasma membrane NADH-dehydrogenases in rat brain tissue

Transplasma membrane redox plays a significant role in cellular activation and growth. Six isoenzymes could be prepared from purified rat brain synaptic plasma membrane. Polyclonal antibodies have been prepared against six transplasma membrane oxydoreductases (PMO-I to PMO-VI) and the tissue distribution of the various iso-enzymes have been investigated in adult rat brains by means of immunohistochemistry. PMO-I is densely observed in layers I, IV and V of the parietal cortex, in CA1 of the hippocampus (except for the molecular layer), in the caudate putamen, in the dorsal, granular and ventral parts of the auditory nuclei, in some loci of the vestibular nuclei as well as in the deep cerebellar nucleus and in the granular layer of the cerebellar cortex. PMO-II is mainly located in the polymorphic layer of the dentate gyrus and in the deep cerebellar nucleus and in the granular layer of the cerebellar cortex. PMO-III is abundant in the piriform cortex, in the pyramidal layers of both CA1 and CA2, in the diagonal band of the basal ganglia, in the supraoptic nucleus and in various loci of the magnetocellular paraventricular nucleus of the hippothalamus as well as in the vestibular nuclei from the brain stem. In addition PMO-III is also densely present in motor nuclei (oculomotor, facial, hypoglossal and ambiguus nuclei), in the reticular formation and in the deep cerebellar nucleus as well as in the Purkinje layer of the cerebellar cortex. PMO-IV has a similar location but is less abundant in the vestibular nuclei of the sensory brain stem and in the motor nucleus. PMO-V in contrast is poorly present in most brain areas compared to the other iso-enzymes, apart of the Purkinje layer of the cerebellar cortex. Finally PMO-VI is mainly present in the oriens layer and in the stratum radiatum of the hippocampus formation, in the supraoptic and lateral magnocellular nucleus of the hypothalamus, in the mesencephalic trigeminal nucleus, in the ventral auditory nucleus and in the facial nucleus of the brain stem as well as in red nucleus of the reticular formation and in the Purkinje layer of the cerebellar cortex. These data show that the iso-enzymes are located in specific brain nuclei. The significance of the results in respect to the yet very poorly defined function of PMO's is discussed.

An NADH-diaphorase is located at the cell plasma membrane in a mouse neuroblastoma cell line NB41A3

Plasma membranes from most mammalian cells display significant transplasma membrane oxidoreductase (PMO) activity. The enzymes use an extracellular, impermeant electron acceptor as substrate and intracellular reduced pyridine nucleotide as electron donor. The plasma membrane from a neuroblastoma cell line, NB41A3, has been biotinylated and purified by immunoprecipitation with avidin and antiavidin-antibodies. The protein recovery of an immunopurified membrane preparation was < 0.15% of the protein content in the cell extract. The preparation displays an increase in the specific activity of PMO's of 15- to 20-fold compared to the activity in whole cells. With this approach the presence of a NADH-diaphorase within the cell plasma membrane can be demonstrated. This activity accounts for about one third of the total cellular diaphorase activity. The PMO activity cannot be attributed to an increased permeabilization of the plasma membrane induced upon biotinylation nor to intracellular activity from lysed cells. Activation of basal metabolism (glycolysis) stimulates PMO activity up to approx. 54%, presumably through a raise of the intracellular NADH store. PMO also promotes cell growth at low substrate concentrations (0.1-1 microM). Native gel electrophoresis of iminobiotinylated and affinity purified plasma membrane extracts displays two diaphorase-positive bands, indicating that a homogeneous cell population may express several PMO activities at the plasma membrane.

Manipulation of plasma membrane fatty acid composition of fetal rat brain cells grown in a serum-free defined medium

Modifications of plasma membrane acyl-linked phospholipid fatty acid composition were produced by supplementing the culture medium with essential fatty acids. The plasma membrane fraction was purified by Percoll gradient centrifugation from dissociated fetal rat brain cells grown in a serum-free culture medium. Both the concentration dependence and the time course of the modifications were examined. Supplementation of the medium with essential polyunsaturated fatty acid, linolenic acid (18:3 omega 3) or linoleic acid (18:2 omega 6), produced incorporation of the elongated and desaturated products of omega 3 or omega 6 class, respectively, i.e., the incorporation was class specific. Within each class, the most unsaturated and elongated members, i.e., terminal members, were preferentially incorporated until they reached a maximum concentration within 6-7 days. At higher concentrations of supplemented fatty acids, additional class specific incorporation in plasma membrane was produced by an increase in the concentration of intermediate members. At the same time, the concentration of monounsaturated fatty acids declined and that of saturated fatty acids remained unchanged. The modifications in fatty acid composition were reversible, with the time course similar to that of incorporation. The total plasma membrane phospholipid and sterol contents did not change with alterations of fatty acid composition, but did change with time in culture. This preparation should prove useful for investigating the role of polyunsaturated fatty acids in brain cell functions, including neuronal excitability.

Plasma membrane dehydrogenases in rat brain synaptic membranes. Multiplicity and subunit composition

Plasma membrane redox enzymes have been investigated in synaptic membranes from rat brain nerve terminals. UV-Vis spectra of intact synaptic plasma membranes are presented and the presence of a b-type cytochrome, detectable at 77 degrees K and sensitive to NADH or NADPH, is shown. The molecular characterization of rat synaptic NADH-dehydrogenases was further performed on solubilized enzymes using a recently developed nondissociating polyacrylamide gel electrophoresis technique. Synaptic plasma membranes were solubilized with 1% sodium cholate or Triton X-114 and centrifuged. The supernatant retained over 60% of the NADH-dehydrogenase activity, tested with either DCIP2 or ferricyanide as substrates, together with NADH. Both enzyme activities were insensitive toward rotenone. This extraction procedure also solubilized about 50% of the proteins. When submitted to polyacrylamide gel electrophoresis under nondenaturing conditions and stained for NADH-dehydrogenase activity, five bands of different mobilities were detected. The multiple NADH-dehydrogenases of synaptic plasma membranes were investigated by means of band excision and the five excised bands each submitted to amino acid analysis and to 2-D electrophoresis. The subunit composition of each band was then deduced, together with the molecular weight and pI of each respective subunit. NADH-dehydrogenases have also been purified by means of FPLC on Mono-P (chromatofocusing) followed by gel filtration on Superose 12. NADH-Dehydrogenase IV and V could be purified in their active forms by this approach.

Identification and isolation of an axonal plasma membrane enriched fraction from cerebellar granule cell neurites

A procedure is described to isolate a fraction enriched in cerebellar granule cell neuritic membranes. Morphological markers that are specific for either the granule cell perikarya or neuritic membranes have been identified. Concanavalin A (Con A) has been shown to bind predominantly to the granule cell neurites whereas, the enzymes acetylcholinesterase (AChE) and 2',3',cyclic nucleotide-3'-phosphohydrolase (CNPase) are localized predominantly in the neuronal cell bodies. The membrane fraction enriched in Con A binding has been used to generate a monoclonal antibody which morphologically recognized the cerebellar granule cell neuritic membrane. Following fractionation of the granule cells, each marker was used to identify the cellular origin of the fractions. The neuritic markers Con A and the neuritic membrane antibody MR2 bound predominantly to membranes found in the 29.1% and 31.5% region of the sucrose gradient. The perikaryal markers, CNPase and AChE activity were most enriched in membrane fractions found at a sucrose concentration of 23% and 21%, respectively. Morphological examination of the neuritic enriched fraction shows that it contains predominantly membranous material with few subcellular organelles. The protein profiles of the cerebellar granule cell fractions are unique when compared with the protein profiles of other neuronal and non-neuronal fractions. The membrane fraction isolated from the cerebellar granule cells should prove useful in furthering our understanding of the axonal influence on glial development.

Effect of cell surface trypsinization on ethanolamine base exchange enzymatic activity of astrocyte primary cultures and derived spontaneously transformed cell lines

Trypsinization of neonatal rat astrocyte primary cultures (normal cells) inhibited the activity of ethanolamine base exchange enzyme (EBEE) by 80%, whereas ethanolamine phosphotransferase (EPT) and choline base exchange (CBEE) enzymatic activities were not affected; subcellular fractionation demonstrated that trypsin treatment affected the intracellular EBEE activity. During trypsinization the enzyme was not taken up by cultured astrocytes but the cell surface was affected. In contrast, the same treatment did not alter EPT, CBEE and EBEE activities of spontaneously transformed cell lines derived from the primary cultures. However, treatment of the transformed cells with db-cAMP prior to trypsin, restored the pattern found in the primary culture, i.e. only EBEE activity was affected. These data suggest that a relationship exists between cell surface organization and intracellular EBEE activity in a culture system which possesses the property to control its own cell division or/and differentiation.

The 43-kDa neuronal growth-associated protein (GAP-43) is present in plasma membranes of rat astrocytes

One of the neuronal growth-associated proteins, GAP-43 (molecular mass, approximately 43 kDa; pI 4.3), is abundant in growth-cone membranes and corresponds to a major protein kinase C substrate, the 46-kDa phosphoprotein (pp46), of a growth-cone-enriched subcellular fraction. This protein has the following additional designations (depending on context): B-50 (phospholipid metabolism), F1 (synaptic plasticity), and p57 (calmodulin binding). We show that a protein with the same molecular mass and isoelectric point as GAP-43, which interacts with anti-GAP-43 antibodies on immunoblots, is present in the plasma membranes of cultured neonatal rat cortical astrocytes. Double-immunofluorescence labeling of cells with a serum against glial fibrillary acidic protein and anti-GAP-43 antibody was observed. Furthermore, astrocytic protein was phosphorylated in vitro by protein kinase C and comigrated in two-dimensional PAGE with GAP-43. The data indicate that GAP-43, heretofore believed to be neuron-specific, is present in at least one class of glial cells.

The anticonvulsant sodium valproate specifically induces the expression of a rat glial heat shock protein which is identified as the collagen type IV receptor

A potential mechanism for valproate (VPA)-induced increases in glial cell-substratum adhesivity has been demonstrated. Metabolically labelled glioma (C6) and primary astrocytes showed a statistically significant accumulation of protein when cultured in the presence of therapeutic concentrations of VPA (1 mM). This was mainly accounted for by a 10-fold increase in the production of a single polypeptide of 43 kDa molecular weight. Fractionation studies and metabolic labelling with N-acetyl-D-mannosamine showed this to be a sialoglycoprotein which was plasma membrane-bound. VPA-induction of the polypeptide was apparently specific to glioma and primary astrocytes and was not observed in neuroblastoma (neuro-2a), fibroblasts (3T3), pituicytes (GH3) and epithelial cells (NCTC). The 43 kDa component of glia was demonstrated to be the receptor for type IV collagen by binding metabolically labelled and solubilised cells to Sepharose beads which had been individually coated with laminin, fibronectin and type IV collagen. The protein has also been shown to be a heat shock product as metabolically labelled glioma showed a 10-fold increase in its expression when cultured at 42 degrees C. This heat shock induced expression was transient and was in marked contrast to that seen with VPA where it increased with time and was sustained. The expression of 43 kDa is suggested to arise by VPA and heat shock induced delays in cell cycle progression and this is discussed in relation to teratogenic action.

Studies on oxygen and volume restriction in cultured cardiac cell: possible rearrangement of sarcolemmal lipid moieties during anoxia and ischemia-like states

Cultured heart cells have been shown useful for investigating states of oxygen and volume restrictions, simulating anoxia and ischemia-like states at cellular levels. The sarcolemma has been implicated as one of the early sites of ischemic damage; therefore, lactoperoxidase catalyzed radioiodination was used to study accessibility of the sarcolemmal lipid moieties to this enzymatic probe, reflecting their exposure to the extracellular environment, hence the biophysical state of the sarcolemma. These studies have shown that within one hour of 'ischemic' injuries: (1) The degree of labelling in the total phospholipid fraction is considerably increased; and (2) Profound changes in the relative extent of labelling of different phospholipid classes were observed. The PE/PC labelling ratio increases dramatically with the progress of ischemia-like state. We suggest that early during ischemic injury, reorganization of the cell surface phospholipids occurs and discuss possible relations to the energy charge of the cell.

Isolation of plasma membranes from neurons grown in primary culture

Plasma membranes from chick embryo neuronal primary cultures were isolated after subjecting 5-day-old cells, previously surface labeled with either lactoperoxidase-catalyzed radioiodination or galactose oxidase/NaB3H4, to a freeze-thaw cycle. The cellular material adhering to the culture substratum was washed, and the "wash" fractions were pooled and centrifuged at 37,000g. The resulting pellet was resuspended in 3 ml of buffer, layered on 33 ml of 33% sucrose, and centrifuged at 105,000g. Radioactivity was recovered at the top of the gradient. Sedimentation of these fractions and biochemical studies revealed that the pellet was 20- and 12-fold enriched in (Na+,K+)-adenosinetriphosphatase and 5'-nucleotidase, respectively. The preparation was devoid of inner mitochondrial (succinate dehydrogenase), outer mitochondrial (monoamine oxidase), endoplasmic reticulum (glucose-6-phosphatase), outer mitochondrial (monoamine oxidase), endoplasmic reticulum (glucose-6-phosphatase), and Golgi (UDP galactose:N-acetylglucosamine galactosyltransferase) enzymatic markers. Ultrastructural studies showed that the membrane preparation was homogeneous and lacked mitochondria endoplasmic reticulum and lysosomes. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate showed the presence of 11 protein components with molecular masses ranging from 120 to 300 kDa. This method for the isolation of plasma membranes probably depends on the capacity of the cellular material to adhere to the culture substratum and to entrap intracellular organelles during the freeze-thaw cycle. The membrane preparation seems suitable for studying the function of high-molecular-weight protein components of neuronal plasma membranes.

Characterization of two plasma membrane proteins abundant in rat brain

Plasma membranes were isolated from rat brain cortices and their proteins characterized by two-dimensional electrophoresis. Approximately 500 polypeptides with relative molecular weights (mol. wt.) between 20 kDa and 120 kDa and isoelectric points (pI) between 4.2 and 8.5 were visualized by silver staining. Two proteins, MP1 and MP2, comprised about 5% each of the total by mass. Their mol. wts. were 56 kDa and 43 kDa, and their pIs were 4.2 and 4.3, respectively. The two proteins were present in membranes of cultured granule neurons and cortical astrocytes and absent in liver and kidney. They were both substrates for phosphorylation by protein kinase C. MP2 is similar, if not identical, to a major phosphoprotein in growth cones, pp46 (also termed GAP-43, B-50, F1).

Ethanolamine base exchange in astrocyte primary cultures: localization and developmental studies

The enzymatic activities of ethanolamine base exchange (EBEE) and CDP-ethanolamine: 1,2-diacylglycerol ethanolamine phosphotransferase (EPT) were investigated during the growth of rat astrocyte primary cultures. From the 16th day, cells ceased to divide (2.0 X 10(6) cells per culture dish); the total phospholipid (PL) content increased 1.5 fold between the 16th and 24th day (0.20 to 0.30 mumol per mg protein) but the amount of ethanolamine phospholipid (28% of PL content) remained constant. Whereas the specific activity (pmol/min X mg protein) of EPT reached a plateau at 16 days in culture and remained constant (400) thereafter, that of EBEE increased up to the 19th day (190) and decreased gradually to a basal level (75) at the 24th day. EBEE activity was not detected in plasma membranes isolated from 16, 19 and 24 days astrocyte cultures. Sub-cellular fractionation and determination of EBEE specific activities showed that the 104 X 10(3) g fraction (P4) was 4.8 and 8.8 fold enriched at the 16th day and 24th day respectively as compared to the whole cell homogenate (50 and 75). The 7 X 10(3) g (P2) and 17 X 10(3) g (P3) fractions were 8.4 and 7.0 fold enriched respectively at the 19 day in culture. The percentages of the enzymatic activity in the different subcellular fractions were 30, 57.2 and 25.7 for P2 and 39.2, 2.6 and 39.8 for P4 at 16, 19 and 24 days in culture respectively. The activity remained constant in P3 (23%) and was negligible in P1 (6%). Ultrastructural studies revealed that P2 and P3 were enriched in mitochondria while P4 contained essentially microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)

NAD+ glycohydrolase of the plasma membrane prepared from glial and neuronal cells

NAD+ glycohydrolase (EC 3.2.2.5) activity was detected in the plasma membrane prepared from the primary culture of rat astrocytes. The enzyme has a broad optimum pH range. From the kinetic analysis, a Michaelis constant of 91.2 microM and a maximum velocity of 0.785 mumol/min/mg protein were obtained. ADPribose exhibited a competitive inhibition with respect to NAD. The inhibition by nicotinamide was shown to be of a non-competitive type. ATP and GTP were found to be competitive inhibitors. NAD+ glycohydrolase activity was not detected in the plasma membrane prepared from the primary culture of neuronal cells of chick embryos.

The nature of DT-diaphorase (EC 1.6.99.2) activity in plasma membrane of astrocytes in primary cultures

This is the confirmation of an earlier indication (Mersel, M., Malviya, A.N., Hindelang, C. and Mandel, P. (1984) Biochim. Biophys. Acta 778, 144-154) that the plasma membrane of astrocytes in primary cultures is endowed with DT-diaphorase (EC 1.6.99.2) activity. It is observed that the NADPH-2,6-dichloroindophenol diaphorase activity found in the isolated plasma membrane is not inhibited by dicoumarol. DT-diaphorase-type activity is also observed on the cell surface employing dichloroindophenol as external electron acceptor and it is found to be a dicoumarol-sensitive NADH dehydrogenase.