ATPase activity of neuroblastoma cells in culture

Inhibition of Na+, K+-ATPase activity by delta-aminolevulinic acid

delta-Aminolaevulinic acid (ALA) has been shown to be toxic to cultured neurons and glia at concentrations as low as 10 microM. In an attempt to elucidate the mechanism of toxicity, the effects of ALA on membrane ATPase activity were investigated. Exposure of neuron cultures to 1 mM ALA for 7 days caused a substantial decrease in both Na+, K+-ATPase and Mg2+-ATPase activities. At lower concentrations, ALA affected only the Na+, K+-component. ALA appeared to act directly, inhibiting Na+, K+-ATPase activity in rat brain cortex membrane preparations at 10 microM. Although this effect was slight, it may well represent the mechanism of action of ALA, since ouabain, a potent inhibitor of Na+, K+-ATPase activity, proved to be more toxic to cultured neurons than ALA. Furthermore, cardiac glycoside overdosage causes neurological disturbances which are very similar to those observed in the acute attack of porphyria.

The ATPase activity in brain microtubule preparations is membrane-associated

Microtubule protein prepared from bovine brain by a temperature-dependent assembly-disassembly procedure contained Mg2+- or CA2+-stimulated ATPase activity. However, activity decreased with successive cycles of assembly-disassembly such tht 15% of the Mg2+-stimulated and 31% of the Ca2+-stimulated activity of the second-cycle material remained after seven cycles. Microtubule preparations purified by three cycles of assembly-disassembly contained many membrane fragments and vesicles which were absent in microtubule preparations cycled eight times. Histochemistry and electron microscopy revealed that much of the activity is associated with the vesicles. Vesicles with an accumulation of led phosphate deposits (indication of ATPase activity) were observed in high-speed pellets (150,000 g, 60 min) of microtubule-associated proteins. Most of the activity in the microtubule-associated protein preparations, but only a fraction of the total protein is pelleted. 53-78% of the ATPase activity, but only 6% of the total protein, is recovered in a microtubule-associated protein fraction eluted from phosphocellulose with 0.17 M NaCl. Polypeptides resolved on SDS polyacrylamide gradient gels have estimated molecular weights of 30,000-76,000. Electron micrographs of this material revealed short filaments, vesicles, and small ring-like structures. None of the inhibitors of possible contaminating ATPases affected the ATPase activity.

Effect of hydrocortisone and thyroxine on ATPase activities of neuronal and glial cell lines in culture

The effect of hydrocortisone and thyroxine, on the activities of Ca2+- and Mg2+- ATPase was studied in cultured neuronal (clone M1) and glial (clones NN and C6) cell lines. For M1 and NN cells an increase in Ca2+- and Mg2+-ecto-ATPase activity was found when the cells were cultured during 4-6 days in presence of hydrocortisone or together with thyroxine. In the same conditions, a decrease in Ca2+- and Mg2+-ecto-ATPase activity was found for the C6 cells. In C6 cells the effect of hormones was more pronounced for the Mg2+- than for the Ca2+-ecto-ATPase activity. The observed decrease may be related to the tumoral origin of the C6 cells. The activity of (Na+, K+)-ATPase in all three cell lines increased in presence of hydrocortisone or together with thyroxine when the cells were cultured during 4-6 days, in presence of the hormones, whereas the total Mg2+- ATPase activity increased only after 6 days of treatment. Thyroxine alone has very few effect either on Ca2+- and Mg2+-ecto-ATPase, or on (Na+, K+)- and total Mg2+-ATPase activity. These observations are interpreted to indicate that hormones may modulate or induce enzymatic activities involved in active transport phenomena in nervous tissue.

Study of some enzyme activities in cultured chick embryo brain nerve cells treated by chick embryo brain extracts

Brain extracts from 8-day-old chick embryos have been shown to influence morphological development of dissociated brain cells from 7-day-old chick embryos in culture. Stimulatory effects on size of the neuronal somas and on growth of long processes were observed by adding the cytosol of the brain extract or the dialysate of the cytosol. These morphological changes parallel modifications of various enzyme activities according to the age of the cultures. Adenyl cyclase, (Na+,K+)- and Mg2+-ATPase, 5'-nucleotidase, choline acetyltransferase, and acetylcholinesterase activities were studied between 5 and 14 days of culture. Adenyl cyclase activity was strongly stimulated at 8 days by both extracts. (Na+,K+)- and Mg2+-ATPase activities were stimulated in 8-day-old cultures only by the dialysate. 5'-Nucleotidase activity was stimulated in 8-day-old cultures by the dialysate and in 11-day-old cultures by both extracts. Choline acetyltransferase activity was stimulated by the cytosol in 8-day-old cultures and by the dialysate in 11-day-old cultures. The total acetylcholinesterase activity was higher in 8-, 11-, and 14-day-old cultures treated with the cytosol. When the cells were treated with the dialysate, the activity was only higher in 14-day-old cultures. We also found that following the addition of brain extracts, the specific activity of the enzymes we studied was enhanced and became close to the values found in vivo during embryogenesis. Thus in parallel to the morphological modifications observed in nerve cell cultures treated by embryo brain extracts, biochemical variations especially involved in synaptogenesis and membrane development could be measured.

Ethanol and neuronal metabolism

The effect of ethanol on membrane enzymes (Na+, K+ and Mg2+ ATPases, 5'-nucleotidase, adenylate cyclase) alcohol dehydrogenase, aldehyde dehydrogenase and superoxide dismutase were studied in nerve cells (established cell lines, primary cultures of chick and rat brain) cultured in the presence of 100 mM ethanol, and in total rat brain, following various ethanol treatments of the rats (20% ethanol as the sole liquid source, intraperitoneal injection). The results show a difference between neuronal and glial cells. Most of the observed changes in enzymatic activities returned rapidly to control values when ethanol was withdrawn from the culture medium or from the diet. Alcohol dehydrogenase was more stimulated by ethanol than aldehyde dehydrogenase; therefore acetaldehyde may be accumulated. The inhibition of superoxide dismutase activity may allow an accumulation of cytotoxic O2- radicals in nervous tissue and may explain the polymorphism of lesions brought about by alcohol intoxication.

Inhibition of fast axonal transport and microtubule polymerization in vitro by colchicine and colchiceine

The effects of colchicine and colchiceine on fast axonal transport in frog sciatic nerves were studied in vitro. Colchiceine inhibited the transport to about the same extent as colchicine. Preincubation at low temperature potentiated the inhibitory effect of either drug. The polymerization of purified brain tubulin was inhibited by colchiceine at 5-10 times higher concentrations than colchicine. The similarity of the effects obtained with colchicine and colchiceine indicates that both drugs arrest axonal transport by interfering with microtubule function. Colchicine and colchiceine did not affect the levels of high energy phosphates (ATP and CrP) in frog nerves indicating that a reduced energy supply was not responsible for the arrested transport.

Differences in microtubule stability to colchicine in extracts of guinea pig, rat and rabbit brain

1. Microtubules (MT) from a guinea pig brain 25,000 g supernatant are not depolymerized by colchicine in contrast to MT from similar preparations of rat and rabbit. 2. The colchicine-stability was lost if the guinea pig brain homogenate was centrifuged at a higher g-level, further purified or if only the grey matter was used. 3. The association constant of colchicine to tubulin did not differ between a stable and a labile guinea pig brain preparation. 4. The GTP-hydrolysis was higher in the guinea pig preparation containing stable MT, than in the preparation containing labile MT. Additional GTP added to the polymerized MT before colchicine exposure, labilized the MT. Preincubation with NaF decreased the GTP-hydrolysis and caused a colchicine depolymerization. 5. The results indicate species differences in colchicine sensitivity of in vitro polymerized MT, probably depending on differences in GTP-hydrolysis.

Morphological changes in the cat cerebral cortex produced by superfusion of ouabain

The morphological changes following superfusion of the cat cerebral cortex with ouabain were studied. Autoradiography of [3H]ouabain was performed to study drug distribution. The resulting lesion consists of an upper vacuolated layer which is distinctly separated from an underlying region containing dark neurones. Ouabain is confined to the vacuolated layer. Swelling of apical dendrites and many presynaptic terminals are the main morphological changes occurring in the vacuolar layer. Depletion of synaptic vesicles, clustering of vesicles around the synaptic membrane, and the production of coated vesicles and cisternae are further changes found within presynaptic endings. Whilst swelling of fibrous astrocytes within the glialimitans occurs, this is not true of astrocytic processes elsewhere in ouabain exposed regions. Regions containing dark neurones are characterised by a general swelling of astroglial processes. The results strongly suggest that apical dendrites and presynaptic endings possess high activities of Na+, K+-ATPase whereas the activity on astroglial processes within the neuropil is relatively low. Astroglial swelling in areas of dark neurones is produced by some change in the chemical milieu surrounding the processes which appears unrelated to Na+, K+-ATPase inhibition.

The chronic and acute effects of ethanol on adenosine triphosphatase activity in cultured astroblast and neuroblastoma cells

Mg2+ATPase and (Na+ + K+)ATPase activities were measured in clonal line NN hamster astroblasts and in clonal lines M1 and N1E-115 mouse neuroblastoma cells after the cells had been subjected to the acute and chronic actions of 100 mM ethanol. Exposure of the astroblasts to ethanol for periods as long as 68 days produced an increase in total cellular Mg2+ ATPase activity, as measured in cell homogenates; however, activity reverted to control levels upon withdrawal of ethanol. Chronic exposure of clonal line N1E-115 neuroblastoma cells to ethanol produced an increase in Mg2+ATPase and (Na+ +K+)ATPase activities. In contrast, the activities of both ATPases of clonal line M1 neuroblasts were unaffected by chronic exposure to ethanol. Acute exposure of cell homogenates to 100 mM ethanol inhibited Mg2+ ATPase and (Na+ + K+)ATPase of astroblasts but not that of neublastoma cells. These findings suggest that neural cells in culture may serve as useful models for studying the effects of ethanol on specific cell types.