Monte Carlo Aggregation Code (MCAC) Part 2: Application to soot agglomeration, highlighting the importance of primary particles

During the agglomeration of nanoparticles and in particular, soot, a change in both the flow regime (from free molecular to near continuum) as well as the change of agglomeration regime (from ballistic to diffusive) is expected. However, these effects are rarely taken into account in numerical simulations of particle agglomeration and yet, they are suspected to have an important impact on the agglomeration kinetics, particle morphologies, and size distributions. This work intends to study these properties by using the Monte Carlo Aggregation Code (MCAC) presented in the preceding work (part 1), focusing on the physical impacts of varying the particle volume fraction and monomers size and polydispersity. The results show an important sensitivity of the kinetics of agglomeration, coagulation homogeneity, and agglomerate morphology to the size of monomers. First, for smaller monomer diameters, the agglomeration kinetic is enhanced and agglomerates are characterized by larger fractal dimensions. Second, for large monomer diameters, fractal dimensions down to 1.67 can be found being smaller than the classical 1.78 for Diffusion Limited Cluster Agglomeration (DLCA) mechanism. One important conclusion is that variation in time of both regimes has to be considered for a more accurate simulation of the agglomerate size distribution and morphology.

Monte Carlo Aggregation Code (MCAC) Part 1: Fundamentals

The application of Monte Carlo methods to simulate the agglomeration of suspended nanoparticles is currently limited to specific agglomeration regimes with reduced accuracy in terms of the particle's physical residence time. The definition of specific particles persistent distance, its corresponding time step and subsequent probabilities for particle displacements may improve the accuracy of this method. To solve these issues, a new persistent distance and its corresponding time step based on Langevin dynamics simulations are introduced. Additionally, a probability of particle displacements, not restricted to a specific agglomeration regime, is introduced. All the modifications are validated by comparison with Langevin dynamics simulations. Finally, the above mentioned modifications considerably improve the accuracy of Monte Carlo methods to predict the dynamics and agglomeration of suspended nanoparticles.

Novel TASK channels inhibitors derived from dihydropyrrolo[2,1-a]isoquinoline

TASK channels belong to the family of K(+) channels with 4 transmembrane segments and 2 pore domains (4TM/2P) per subunit. These channels have been related to apoptosis in cerebellar granule neurons (CGN), as well as cancer in other tissues. TASK current is regulated by hormones, neurotransmitters, anesthetics and divalent cations, which are not selective. Recently, there has been found some organic compounds that inhibit TASK current selectively. In order to find other modulators, we report here a group of five dihydropyrrolo[2,1-a]isoquinolines (DPIs), four of them with putative anticancer activity, that were evaluated on TASK-1 and TASK-3 channels. The compounds 1, 2 and 3 showed IC50 < 320 μM on TASK-1 and TASK-3, intermediate activity on TASK-1/TASK-3 heterodimer, moderate effect over hslo and TREK-1 (500 μM), and practically not inhibition on Shaker-IR, herg and IRK2.1 potassium channels, when they were expressed heterologously in Xenopus laevis oocytes. In rat CGN, 500 μM of these three compounds induced a decrement by >39% of the TASK-carried leak current. Finally, only compound 1 showed significant protection (∼36%) against apoptotic death of CGN induced by K(+) deprivation. These results suggest that DPI compounds could be potential candidates for designing new selective inhibitors of TASK channels.

[The 2009 H1N1 flu pandemic in Navarre, Spain]

BACKGROUND

To describe flu activity during the 2009-2010 pandemic in Navarre and compare it to previous seasons.

METHODS

An analysis was made of all flu cases reported in primary care and all the virological confirmations made in patients in primary care and in hospitals of Navarre between week 21 of 2009 and week 20 of 2010.

RESULTS

Influenza A (H1N1) Virus 2009 was detected in Navarre between week 23 of 2009 and week 2 of 2010, a period when 39 medically diagnosed cases of flu syndrome per 1,000 inhabitants were registered. The epidemic threshold was surpassed in two periods, with a peak in July and a greater one in November. The greatest incidence was reached in children aged between 5 and 14 years (121 per thousand), followed by the group of under fives. There were 224 hospitalisations (36 per 100,000 inhabitants) with confirmation of Influenza A (H1N1) Virus 2009, 8% of whom required admission to intensive care units and there were four deaths (0.6 per 100,000 inhabitants). The rate of hospitalisation was greater amongst children under five (163 per 100,000 inhabitants), while the probability of referral to intensive care increased with age.

CONCLUSION

In spite of not having a specific vaccine available until the season was very well advanced, Influenza A (H1N1)Virus 2009 produced a flu wave with similar levels to those of other seasons and its repercussion in hospitalisations and serious cases was moderate.

[Incidence of influenza and influenza vaccine effectiveness in the 2004-2005 season]

BACKGROUND

To quantify the incidence of flu in different groups of the population of Navarra in the 2004-2005 season, and to evaluate the effectiveness of anti-flu vaccination.

METHODS

The analysis of influenza cases in the system of compulsory notificable diseases was complemented by the individualised notifications in the network of sentinel doctors that covers a population of 22,339 inhabitants. The coverage and effectiveness of the vaccine was studied.

RESULTS

Vaccine coverage in (3)65 year olds reached 62%. The incidence of influenza was 42.6 cases per 1,000 inhabitants. It reached a maximum in mid-January, exceeding 750 weekly cases per 100,000 inhabitants and 1,900 cases per 100,000 children. The highest rate of influenza was observed in under-15 year olds (49.4 cases per 1,000 inhabitants) and the lowest in non-institutionalised (3)65 year olds (2.6 per 1,000 inhabitants), although it was higher in geriatric residences (62.1 per 1,000; p<0.0001). Seventy-nine percent of the cases from 5 to 64 years resulted in absenteeism from school or work. The flu virus was identified in 42/65 (65%) nasopharyngeal smears, 90% being influenza virus A(H3). The incidence of influenza was 3.08% in the unvaccinated and 0.45% in the vaccinated (p<0.001). The global effectiveness of the anti-flu vaccine was 65%, and in (3)65 years old it was 73%.

CONCLUSION

Although its effectiveness is not total, the vaccine is the main measure for preventing influenza. The network of sentinel doctors provide useful information for the coordination of care and public health activities against flu.

Role of ionic fluxes in the apoptotic cell death of cultured cerebellar granule neurons

Cultured cerebellar granule neurons (CGC) increase survival in a medium containing 25 mM KCl (K25), and they die apoptotically when cultures are treated with staurosporine (St) or are transferred to a 5-mM KCl containing medium (K5). Apoptotic CGC show nuclear condensation and caspase-3 activation. Cell death induced by these conditions was partially prevented when cultures were maintained under alkaline conditions, which also induced a marked reduction of the caspase-3 activation. The acidification of the medium further increased cell death induced by both stimuli. Cultures transferred to K5 suffered an immediate intracellular alkalinization that remained constant during the time K5 was present. In contrast, St did not modify cytosolic pH at any of the evaluated times. On the other hand, DIDS, furosemide, and bumetanide prevented CGC death induced by K5 and St. Other drugs such as amiloride, EIPA, tamoxifen, NEM, or NPPB did not modify cell death induced by these conditions. Both DIDS and bumetanide markedly inhibited the processing and activation of caspase-3, and DIDS prevented the nuclear condensation induced by K5 and St. These findings suggest that pH is a condition that could contribute to the modulation of cell death induced by some stimuli and that other ions, such as potassium, could have a role in the initial phase of apoptotic death of CGC.

Mechanisms of cell death by deprivation of depolarizing conditions during cerebellar granule neurons maturation

Cerebellar granule cells (CGC) cultured under 5mM KCl (K5) undergo apoptosis after 5 days in vitro (DIV). CGC death is reduced by chronic treatment with 25 mM KCl (K25) or NMDA. Also, when CGC cultured for 6-8 DIV in K25 are transferred to a K5 medium, cells die apoptotically. Moreover, Bcl-2 and Bcl-xL protect neurons from apoptosis, while Bax and Bcl-xS may act as proapototic proteins. It is suggested that these members of the Bcl-2 family may be involved in the cytochrome-c (cyt-c) release to the cytosol. Cytochrome-c is able to form a complex with other proteins to activate a cascade of proteases. In this work, we found that Bcl-2 levels in K5 cells did not show any change during 2-7 days in vitro (DIV); but cells grown with NMDA and K25 displayed an increase (55% approximately) of Bcl-2 from 4 DIV, as compared to control. Under these conditions, Bax levels showed a tendency to decrease with age under control cells and NMDA/K25 induced a reduction of approximately 10% in Bax levels from 4 DIV. On the other hand, in cells maintained in K25 during 7 DIV and then switched to a K5 medium, the levels of Bax showed a consistent decrease (30% after 8h). Under these conditions, the Bcl-2 levels did not show any significant change after 24h. Cytochrome-c levels were unaffected under K5, NMDA and K25 and only a marginal increase of cytochrome-c in the cytosol was detected at 6h after switching. We also found that caspase-9 was only activated under K25-deprivation meanwhile caspase-3 was involved in both protocols. These results suggest that the Bcl-2 family members, caspases activation and cytochrome-c release are involved in CGC death induced by K5 and their participation in this process could be different depending on neuronal maturation in culture.

Induction of sexual activity of male creole goats in subtropical northern Mexico using long days and melatonin

The aim of this study was to determine whether the sexual activity of local male Creole goats in subtropical Mexico can be induced during the non-breeding season by a long-day treatment followed by insertion of two melatonin implants. The experiment was carried out in the Laguna region in the State of Coahuila, Mexico (26 degrees N). Fourteen male goats were allocated to two balanced groups (n = 7 each) according to body and testicular weights. Males were kept together in two separate groups and fed lucerne hay for ad libitum intake and 300 g of commercial concentrate and had free access to water and mineral blocks. The control group remained in open sheds under natural photoperiod and ambient temperature conditions. The experimental group was placed in a light-proof building and exposed to 2.5 mo of long days (16 h of light/d) from November 1 to January 15. On January 16, each male received two s.c. melatonin implants and was exposed to natural photoperiodic changes in an open shed. In the control group, testicular weight exhibited seasonal variations; the highest value occurred on May 30 (146 +/- 10 g). Treated males reached maximum testicular weight earlier (March 15; 147 +/- 11 g), and sperm quality from January to March was higher than that observed in the control group (P < 0.05). Treatment caused an increase in LH pulse frequency (2.0 +/- 0.5 vs 0.3 +/- 0.2 pulse/8 h in February, 4.6 +/- 1.1 vs 0.1 +/- 0.1 pulse/8 h in March; experimental vs control group, respectively). In the control group, plasma testosterone remained low until mid-June and increased thereafter to remain elevated until the end of the study. In the experimental group, elevated plasma testosterone was observed from February to April and from July to November. Treating male goats in subtropical latitudes with artificial long days and melatonin can induce an intense sexual activity during the natural nonbreeding season.

Role of oxidative stress in the apoptotic cell death of cultured cerebellar granule neurons

When cultured cerebellar granule neurons (CGN) are transferred from 25 mM KCl (K25) to 5 mM KCl (K5) caspase-3 and caspase-8, but not caspase-1 or caspase-9,activities are induced and cells die apoptotically. CGN death was triggered by a [Ca(2+)](i) modification when [Ca(2+)](i) was reduced from 300 nM to 50 nM in a K5 medium. The [Ca(2+)](i) changes were followed by an increase in ROS levels. The generation of both cytosolic and mitochondrial reactive oxygen species (ROS) occurred at three different times, 10 min, 30 min and 3--4 hr but only those ROS produced after 3--4 hr are involved in the process of cell death. When CGN cultured in a K5 medium are treated with different antioxidants like scavengers of ROS (mannitol, DMSO) or antioxidant enzymes (superoxide dismutase and catalase) phosphatidylserine translocation, caspase activity, chromatin condensation and cell death is markedly diminished. The protective effect of antioxidants is not mediated through a modification in [Ca(2+)](i). Caspase activation, PS translocation and chromatin condensation were downstream of ROS production. In contrast to H(2)O(2), ROS produced by a xanthine/xanthine oxidase system in CGN cultured in K25 were able to directly induce caspase-3 activation and death that resulted sensitive to z-VAD, a caspase inhibitor. These findings indicate that a reduction in [Ca(2+)](i) triggers CGN death by inducing a generation of ROS after 3--4 hr, which could play a critical role in the initial phases of the apoptotic process including PS translocation, chromatin condensation and the activation of initiator and executor caspases.

Reduction of phospholemman expression decreases osmosensitive taurine efflux in astrocytes

The role of phospholemman (PLM) in taurine and Cl(-) efflux elicited by 30% hyposmotic solution was studied in cultured cerebellar astrocytes with reduced PLM expression by antisense oligonucleotide (AO) treatment. PLM, a substrate for protein kinases (PK) C and A, is a protein that increases an anion current in Xenopus oocytes and forms taurine-selective channels in lipid bilayers. Taurine contributes as an osmolyte to regulatory volume decrease (RVD) and is highly permeable through PLM channels in bilayers. Two antisense oligonucleotides (AO1 and AO2) effectively decreased the expression of the PLM protein by 40% and 30%, respectively, and markedly reduced [(3)H]taurine efflux by 67% and 62%. AO treatment also decreased the osmosensitive release of Cl(-), followed as (125)I. The inhibition of Cl(-) efflux (23% for AO1 and 13% for AO2) was notably lower than for [(3)H]taurine. The contribution of PKC and PKA in the function of PLM was also evaluated in astrocytes. Pharmacological activation or inhibition of PKC and PKA revealed that the osmosensitive taurine efflux is essentially PKC-independent while (125)I efflux is reduced by the PKC blockers H-7 (21%) and Gö6983 (41%). The PKA activator forskolin and dbcAMP increased taurine efflux by 66-70% and (125)I efflux by 21-45%. Norepinephrine increased the osmosensitive taurine efflux at about the same extent as dbcAMP and forskolin, and this was reduced by PKA blockers. These results suggest that PLM plays a role in RVD in astrocytes by predominantly influencing taurine fluxes, which are modulated by PKA but not PKC.

Volume sensitive efflux of taurine in HEK293 cells overexpressing phospholemman

The role of the phospholemman (PLM) on the efflux of taurine and chloride induced by swelling was studied in HEK293 cells overexpressing stable transfected PLM. PLM, a substrate for protein kinases C and A, is a protein that induces an anion current in Xenopus oocytes and forms taurine-selective channels in lipid bilayers. Taurine contributes as an osmolyte to regulatory volume decrease (RVD) and is highly permeable through PLM channels in bilayers. In PLM-overexpressing cells the process of RVD was more rapid and efficient (75%) than in control cells (44%). Also, [(3)H]taurine and (125)I efflux induced by hyposmolarity were markedly increased (30-100%) in two subclones of cells overexpressing PLM. This increased efflux was sensitive to the Cl channel blockers DDF, NPPB and DIDS. Acute treatment of control cells with isoproterenol and norepinephrine induced a significant potentiation (50-60%) of [(3)H]taurine release induced by hyposmolarity. In PLM-overexpressing cells the potentiation by these drugs was higher (100%). Insulin induced also an increase in [(3)H]taurine release, but only in PLM-overexpressing cells (50%). These results indicate that PLM may play a role in the RVD and that its phosphorylation may have a physiological significance during this process. The mechanisms involved in this process could include the activation of PLM itself as channel or the modulation of other preexisting channels.

Role of heat shock proteins in the effect of NMDA and KCl on cerebellar granule cells survival

Cerebellar granule cells (CGC) die apoptotically after five days in culture (DIV) at physiological concentrations of potassium (5 mM; K5). When CGC are depolarized (K25) or treated with NMDA (150 microM) cell survival is increased. CGC changed from K25 to K5 die after 24-48 h. It is known that heat shock protein (HSP) may protect from cell death. Here, we found that cells in K5 showed an increase in HSP-70 levels after 3 DIV. Similarly, in cells changed from K25 to K5, HSP-70 levels were increased after 6 h. Neither NMDA nor K25 treatment affected HSP-70 levels from 2-7 DIV. Ethanol or thermal stress induced HSP-70, but cell survival was not affected in K5 medium. These results suggest that HSP, particularly HSP-70, are not involved in the mechanisms by which NMDA and KCl promote cell survival.

Release of taurine in apoptotic cerebellar granule neurons in culture

Cell shrinkage is a distinctive feature of apoptotic death, but the mechanisms leading to cell volume loss are unclear at present. Activation of pathways extruding intracellular osmolytes such as K+, Cl- and organic molecules may be part of these mechanisms. This was examined in the present work measuring the release of taurine, gamma-amino-butyric acid (GABA) and glutamate in cerebellar granule neurons cultured in conditions resulting in apoptotic death after 4-7 days in vitro (DIV). The basal release of [3H]taurine from cells started to increase (38%) after 3 DIV and reached a maximal enhancement (250%) at 5 DIV. The increase in taurine efflux closely followed the occurrence of apoptotic death markers such as caspase induction and chromatin condensation. The efflux of glutamate (traced as D-aspartate) and [3H]GABA also increased but notably less than that of taurine (90% and 75%, respectively) at 5 DIV. Taurine release associated with apoptosis was unaffected by 4,4'-diisothiocyanatostilbene 2,2'-disulphonic acid (DIDS) and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), blockers of the diffusive pathway activated during cell volume regulation in hyposmotic conditions. Taurine efflux was increased in Cl(-)-free (replaced by gluconate) and decreased in Na+-free media. Blockers of the energy-dependent glutamate and taurine carriers, dihydrokainate and guanidinoethane sulfonate, respectively, did not affect the release associated with apoptosis. These results implicate taurine in the mechanism of cell shrinkage during apoptosis.

[Multicenter study on the efficacy of advice for the prevention of alcoholism in primary health care]

BACKGROUND

The aim of this study was to analyse and to verify the efficacy of systematic advice for alcoholism prevention, assessing the reduction of the number in risk drinkers.

PATIENTS AND METHODS

A multicenter randomized controlled clinical trial was designed, to perform in general practitioner setting, on a sample of risk drinkers (alcohol intake > 280 g weekly, without dependence) sent by random in intervention group (systematic brief advice with support material and a five visit program during a year) and control group (once brief advice and a control in 1 year). The procedure to incorporate in both groups included physical exam, a blood test and the MALT questionnaire. A descriptive and analytic study on included variables was realised, assessing the percentage of drinkers who reduced alcohol intake below risk limit at the end of a year follow up, as well as the reduction intake in each group.

RESULTS

Of the 139 included males, 75 were in the intervention group and 64 in the control group. The percentage of patients not excluded by MALT > 10, and/or liver disease, that finished the 1 year follow up, was 46%, being the sample average age of 43 +/- 11.8. Patients included in both groups were initially comparable. At the end of a year follow up there were statistically significant differences in: percentage of risk drinkers who decreased alcohol intake below 280 g weekly (82% intervention group; 47% control group); percentage of reduction in GPT, GGT, triglycerides, systolic blood pressure and the MALT questionnaire.

CONCLUSIONS

The efficacy of isolated advice of general practitioner was proved to achieve the alcohol intake reduction below the risk limit accepted in male risk drinkers without alcohol dependence. The systematic follow up during a year significantly improves the results achieved with the isolated advice.

Volume regulation in NIH/3T3 cells not expressing P-glycoprotein. I. Regulatory volume decrease

Exposure of NIH/3T3 fibroblasts not expressing P-glycoprotein to 50, 30, 20, and 10% hyposmotic solutions led to cell volume increases of 70, 32, 21, and 12%, respectively. After swelling, NIH/3T3 cells exhibited regulatory volume decrease (RVD), attaining complete volume recovery after 30 min except in 50% hyposmotic solution, in which volume recovery was 76%. RVD was accelerated by gramicidin and inhibited by the Cl channel blockers 5-nitro-2-(3-phenylpropylamino)-benzoic acid, 1,9-dideoxyforskolin, dipyridamole, and niflumic acid and by the K channel, blocker quinidine. RVD was reduced 15% by removal of extracellular Ca. The pathway opened by hypotonicity was highly permeable to K and Rb and only partly permeable to other cations. Most anions were able to permeate, with a permeability ranking of nitrate > benzoate = iodide > thiocyanate > chloride > > gluconate. The pathway was permeable to neutral amino acids, with a permeability ranking of glycine > alanine > glutamate > taurine > gamma-aminobutyric acid > glutamine. The pathway was not permeable to basic amino acids. These results show that, despite the absence of P-glycoprotein, NIH/3T3 cells exhibit RVD with properties similar to those expressed in most cell types.

Volume regulation in NIH/3T3 cells not expressing P-glycoprotein. II. Chloride and amino acid fluxes

The osmolyte function of amino acids and Cl in native NIH/3T3 cells not expressing the P-glycoprotein was examined by investigating the free amino acid concentration and the swelling-activated efflux of [3H]taurine, as representative of amino acids, and of 125I, as a tracer for Cl. Taurine and 125I efflux was activated by 20 and 30% hyposmotic solutions. At 50% hyposmotic solutions, the osmolyte pool was essentially depleted. The Cl channel blockers 5-nitro-2-(3-phenylpropyl-amino)benzoic acid, 1,9-dideoxyforskolin, dipyridamole, and niflumic acid inhibited the release of the two osmolytes by 80-95%. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (400 microM) decreased the efflux of taurine 80% without affecting that of 125I. Linolenic and arachidonic acids (5-20 microM) showed a concentration-dependent inhibitory effect on taurine and 125I fluxes. Omission of Ca decreased osmolyte fluxes by 16%. Verapamil inhibited the osmolyte release only at 500 microM. Nimodipine at 25 and 50 microM decreased the release of [3H]taurine and 125I by approximately 60 and 80%, respectively, but this effect was independent of the presence of extracellular Ca. These results indicate that amino acids and Cl function as osmolytes during regulatory volume decrease in native NIH/ 3T3 cells.

Regulatory volume decrease and associated osmolyte fluxes in cerebellar granule neurons are calcium independent

To investigate a possible role for Ca as a transduction signal for regulatory volume decrease (RVD), the effects of external Ca removal, Ca channel blockers (Cd, Co, La, Gd, verapamil, diltiazem, dihydropyridines) and inhibitors of endoplasmic reticulum Ca release (dantrolene, ryanodine, TMB-8) were examined on RVD and on the swelling-activated efflux of two main osmolytes: Cl (traced by 125I) and [3H]taurine. Omission of Ca plus EGTA did not affect RVD or osmolyte release but when BAPTA was the chelator, RVD decreased 20%, 125I fluxes were unaffected and taurine stimulated efflux decreased (20%) while the basal efflux slightly increased (<10%). Verapamil, diltiazem, Co, Cd, La and Gd did not affect RVD or osmolyte fluxes. Nimodipine and nitrendipine (25-50 microM) markedly decreased RVD and osmolyte fluxes (>90%) through a mechanism independent of extracellular Ca. Swelling elicited an increase in cytosolic Ca measured by fura-2, which was notably variable ranging 50-350 nM. However, RVD and osmolyte fluxes were not affected by the blockers of endogenous Ca release dantrolene, ryanodine and TMB-8 or by the permeable Ca chelator BAPTA-AM, even when the cytosolic Ca increase was abolished by the chelator. These results indicate that 1) RVD and osmolyte fluxes are independent of extracellular Ca 2) RVD, osmolyte release and cytosolic Ca raise are only coincident events. Consequently, Ca is unlikely to be a transducing signal for RVD in neurons.

Changes of actin cytoskeleton during swelling and regulatory volume decrease in cultured astrocytes

Swelling of cultured astrocytes exposed to hyposmotic medium modified the organization of the filamentous actin (F-actin) cytoskeleton, making the actin network diffuse in the cell body but concentrated at foci corresponding to the tips of the cell projections retracted by swelling. This change was reversible, and, after 2 h, the actin cytoskeleton tended to recover, and cells regained their flat and stellate shape. Cytochalasins B and D (CB and CD, respectively), which disrupt the actin cytoskeleton, did not affect regulatory volume decrease (RVD) or the swelling-activated efflux of Cl- and inositol, although 10 microM CD increased the basal efflux of taurine. The mercurial p-chloromercuribenzenesulfonate (0.5-1 mM), known to disrupt the membrane cytoskeleton in isosmotic conditions, induced a 46, 50, and 38% release of [3H]taurine, 125I, and [3H]inositol, respectively, causing cell shrinkage and retraction of the cytoskeleton. Coincidently, the swelling-stimulated release of [3H]taurine and 125I was reduced by 60 and 30%, respectively. Results of this study do not exclude the possibility that changes in the actin cytoskeleton elicited by swelling are involved in mechanisms of RVD and only indicate that the disruption caused by cytochalasins is unrelated to that process.

Characterization of the activation of glutaminase induced by N-methyl-D-aspartate and potassium in cerebellar granule cells

Chronic stimulation of cerebellar granule cells with N-methyl-D-aspartate (NMDA) or KCI induces a specific activation of the enzymes directly involved in glutamate neurotransmitter synthesis. Phosphate-activated glutaminase (PAG) activity is enhanced in cultured granule neurons incubated with 150 microM NMDA or 25 mM KCI. Other enzymes are not affected by this treatment like lactate dehydrogenase (LDH) and glutamate dehydrogenase (GLDH), which is also a mitochondrial enzyme but not directly involved in neurotransmitter synthesis. This effect is dependent on protein synthesis and is induced after 12 hr of NMDA or KCI stimulation. Kinetics of PAG activity showed that Km values were unaffected, in contrast to Vmax values that were increased approximately 70% and 215% over control by NMDA and KCI treatment, respectively. For GLDH, we found two isoforms that were affected differentially by the experimental conditions. Western blot analysis clearly evidenced an increase of approximately 120-180% in the amount of PAG in NMDA- and KCI-treated cells, whereas GLDH was not significantly modified. These results demonstrate that the NMDA- and KCI-induced activation of PAG are not due to the modification of the preexisting enzyme, but to an increase in the synthesis of this enzyme. This suggests that NMDA receptor stimulation during critical periods of the cerebellar granule cell development leads to the activation of gene expression involved in the process of cell differentiation.

Taurine deficiency in dissociated mouse cerebellar cultures affects neuronal migration

The role of taurine in the process of neuronal migration was studied in a microwell cell culture system. Immunocytochemical analysis of the cellular composition of this culture system revealed the presence of the astrocytic marker GFAP in some structures such as the aggregates of neuronal bodies and in those cables used for migration, resembling what is described in vivo. The neuronal marker gamma-enolase stained practically all structures, including the aggregates and all cables. The intracellular taurine concentration was reduced by 60% in mouse cerebellar granule cells treated with a blocker of taurine transport, guanidinoethane sulfonate (GES). Under these conditions cell migration was markedly reduced to approximately 50% of that in untreated cultures. Both, taurine depletion and impairment of cell migration induced by GES were prevented by adding taurine to the culture medium. Taurine deficiency similarly affected different morphological parameters such as the number of cables suitable for neuronal migration as well as the number of migrating neurons. The number of aggregates of neuronal bodies was significantly increased, by about 30%, as a consequence of the reduced migration. Taurine alone did not exert any effect on the parameters evaluated. GES treatment of granule cells did not affect mitochondrial metabolism or K(+)-stimulated Ca(2+)-dependent [3H]-D-aspartate release. This suggests that the described effects of taurine deficiency were not due to an alteration of neuronal viability and that the action of GES was not simply due to unspecific and deleterious effects. These results are in agreement with those obtained in in vivo studies. This approach represents a useful model to investigate the role played by taurine in the process of neuronal migration.

Inhibition by dihydropyridines of regulatory volume decrease and osmolyte fluxes in cultured astrocytes is unrelated to extracellular calcium

The 1,4-dihydropyridines (DHP), nimodipine (NMD) and nitrendipine (NTD) were potent blockers of regulatory volume decrease (RVD) and the volume-associated release of [3H]taurine and chloride (measured as 125I) in 2-weeks cultured rat cerebellar astrocytes. The IC50 were 30 microM and 29 microM for taurine efflux and 26 and 27 microM for C1 efflux for NMD and NTD, respectively. Inhibition by DHP was independent of extracellular Ca, as the effect was the same in media with 1 mM Ca or without Ca and 0.5 mM EGTA. DHP did not affect the basal (isosmotic) release of [3H]taurine or 125I inhibition by DHP (measured only on [3H]taurine efflux) was the same in 3-4 weeks cultured cerebellar astrocytes, 2-4 weeks cultured cortical astrocytes and 2-weeks cultured cerebellar astrocytes treated with dibutyril cAMP. Diltiazem (50 microM) and verapamil (100 microM) failed to inhibit RVD or osmolyte efflux.

Inhibition by polyunsaturated fatty acids of cell volume regulation and osmolyte fluxes in astrocytes

The polyunsaturated fatty acids, arachidonic, linoleic, and linolenic acids, were potent blockers of regulatory volume decrease (RVD) and of the swelling-activated efflux of [3H]taurine, D-[3H]aspartate, [3H]inositol, and 125I (used as marker of Cl) from rat cerebellar astrocytes in culture. The monounsaturated oleic and ricinoleic acids and saturated fatty acids were ineffective. The amino acid and 125I fluxes were similarly inhibited by fatty acids, whereas inositol release was less sensitive. Polyunsaturated fatty acids appear to directly affect RVD in trypsinized astrocytes as the inhibition was immediate and fully reversible. Blockers of the arachidonic acid metabolic pathways, indomethacin (cyclooxygenase), esculetin (lipoxygenases), and metyrapone (P-450 monooxygenases), did not prevent the effect of arachidonic acid, suggesting that further metabolism is not required for displaying the effects of arachidonic acid on RVD and osmolyte fluxes. Some blockers of arachidonic acid metabolic pathways, such as nordihydroguaiaretic acid (lipoxygenases) and naphthoflavone (P-450 monooxygenases), also exhibited marked inhibitory effects on RVD and on osmolyte fluxes. The predominant arachidonic acid metabolite in astrocytes, 12-hydroxyeicosatetraenoic acid, did not affect RVD or osmolyte fluxes. These results suggest that arachidonic acid and other polyunsaturated fatty acids directly inhibit the permeability pathways correcting cell volume after swelling in cultured astrocytes.

Selective neurotoxicity of ruthenium red in primary cultures

The inorganic dye ruthenium red (RuR) has been shown to be neurotoxic in vivo when injected intracerebrally. In this work the toxicity of RuR was compared in primary cultures of rat cortical neurons, cerebellar granule neurons and cerebellar astroglia. Microscopic examination of the cultures revealed that RuR penetrates the somata of both types of neurons used and produces vacuolization and loss and fragmentation of neurites. In contrast, no RuR was seen inside cultured astrocytes and no morphological signs of damage were observed in these cells. RuR toxicity was also assessed by immunocytochemistry of alpha-tubulin and by biochemical measurement of the reduction of (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) by the cultured cells. The morphological alterations in the neurons were closely correlated with loss of tubulin immunoreactivity and particularly with a notable decrement in the ability to reduce MTT. Using the latter parameter, it was found that neuronal damage was independent of the age of the cultures, augmented progressively with time of incubation with RuR, from 8 to 24 h, and showed a clear dose-response curve from 20 to 100 microM RuR. Astrocytes showed only a slight decrease in MTT reduction after 24 h of incubation with 100 microM RuR. It is concluded that RuR seems to be toxic for neurons but not for astroglia, and that this selectivity is probably related to the ability of the neurons to internalize the dye. The possible mechanisms of RuR penetration and neuronal damage are discussed.

Sulfhydryl groups essential for the volume-sensitive release of taurine from astrocytes

The volume-sensitive [3H]taurine efflux from cultured astrocytes was found to be strongly inhibited by the sulfhydryl group-modifying reagent N-ethylmaleimide (NEM). This maleimide inhibited taurine efflux evoked by 50% hyposmotic solutions with an IC50 of 54 microM. The inhibition by NEM followed pseudo-first order reaction kinetics. A double log plot of the pseudo-first order constant against NEM concentration gave a linear relationship with a slope of 1.2. The data are consistent with a simple bimolecular reaction mechanism in which one molecule of NEM reacts with one sulfhydryl group per transport unit. The membrane-impermeant maleimide derivative 5-eosin maleimide did not affect the volume-stimulated taurine efflux. The sulfhydryl-modifying mercurial reagents mersalyl and p-chloro mercuribenzenesulfonate (0.5-1 mM) increased [3H]taurine efflux under isosmotic conditions and concomitantly decreased the hyposmolarity-evoked efflux. The results demonstrate an essential requirement for sulfhydryl groups for the volume-sensitive taurine efflux.

Properties of osmolyte fluxes activated during regulatory volume decrease in cultured cerebellar granule neurons

Efflux pathways for amino acids, K, and Cl activated during regulatory volume decrease (RVD) were characterized in cultured cerebellar granule neurons exposed to hyposmotic conditions. Results of this study favor diffusion pores (presumably channels) over energy-dependent transporters as the mechanisms responsible for the efflux of these osmolytes. The selectivity of osmolyte pathways activated by RVD was assessed by increasing the extracellular concentrations of cations, anions, and amino acids to such an extent that upon opening of the pathway, a permeable compound will enter the cell and block RVD by reducing the efflux of water carried by the exit of intracellular osmolytes. The cationic pathway was found selective for K (and Rb), whereas the anionic pathway was rather unselective being permeable to Cl, nitrate, iodine, benzoate, thiocyanate, and sulfate but impermeable to gluconate. Glutamate and aspartate as K but not as Na salts were permeable through the anion channel. RVD was slightly inhibited by quinidine but otherwise was insensitive to known K channel blockers. RVD was inhibited by 4,4'-diisothiocyanostilbene-2-2'-disulfonic acid (DIDS), niflumic acid, and dipyridamole. Gramicidin did not affect cell volume in isosmotic conditions but greatly accelerated RVD, suggesting that cell permeability to Cl is low in isosmotic conditions but increases markedly during RVD making K permeability the rate limit of the process. The permeability pathway for amino acids activated during RVD as permeable to short chain alpha- and beta-amino acids, but excluded glutamine and basic amino acids.

Impaired cell volume regulation in taurine deficient cultured astrocytes

Taurine concentration was reduced by 40 and 65%, respectively in rat cerebellar astrocytes grown in a chemically defined medium or in culture medium containing a blocker of taurine transport (GES). Cell volume in these taurine deficient cells was 10%-16% higher than in controls. When challenged by hyposmotic conditions, astrocytes release taurine and this efflux contributes to the volume regulatory decrease observed in these cells. Taurine deficient astrocytes showed a less efficient volume recovery as compared to controls with normal taurine levels. Exposed to 50% hyposmotic medium, astrocytes with normal taurine concentration recovered 60% of their original volume whereas taurine deficient cells recovered only 30-35%. Similarly, in 30% hyposmotic medium, taurine deficient astrocytes recovered only 40% as compared to 75% in controls. No compensatory increases in the efflux of other osmolytes (free amino acids or potassium) were observed during regulatory volume decrease in taurine deficient astrocytes.

Regulatory volume decrease in cultured astrocytes. II. Permeability pathway to amino acids and polyols

The permeability of the hyposmolarity-activated pathway to amino acids and polyols in cultured astrocytes was examined following the change in rate and direction of regulatory volume decrease (RVD) when the extracellular concentration of the osmolytes was increased to reverse their intracellular-extracellular concentration gradient. Activation of the pathway by swelling would allow those permeable osmolytes to enter the cell and inhibit RVD. The pathway was found to be permeable to neutral amino acids, with beta-amino acids (beta-alanine = taurine > gamma-aminobutyric acid) more permeable than alpha-amino acids. Glycine, alanine, threonine, phenylalanine, and asparagine, but not glutamine, were permeable through this pathway. Aspartate was more permeable than glutamate, and K+ and not Na+ must be the accompanying cation. Basic amino acids were excluded. The dimension of the amino acid pore activated by hyposmolarity seems to be at the limit of glutamate-glutamine size. Influx rather than efflux of amino acids was observed when extracellular concentration was greater than intracellular concentration, with differences in the amount accumulated by cells correlating with their efficiency as RVD blockers. Influx of taurine (as representative of permeable amino acids) was inhibited by the Cl- channel blockers/exchangers 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (40%) and dipyridamole (85%) , and it is suggested that amino acids permeate through an anion channel. Sorbitol and mannitol, but not inositol, exhibited a small inhibitory effect on the later phase of RVD, whereas inositol slightly accelerated RVD.

Regulatory volume decrease in cultured astrocytes. I. Potassium- and chloride-activated permeability

Regulatory volume decrease (RVD) in detached cerebellar astrocytes in culture after acute exposure to hyposmolarity was characterized in this and the accompanying paper [H. Pasantes-Morales, R. A. Murray, R. Sanches-Olea, and J. Moran. Am. J. Physiol. 266 (Cell Physiol. 35): C172-C178, 1994]. RVD was independent of extracellular calcium, was accelerated at pH 8-9 and retarded at pH 6, and was reduced at temperatures < 18 degrees C. The cationic pathway activated by hyposmolarity was specific for K+ and Rb+, since RVD was abolished and secondary swelling occurred when these ions replaced Na+. However, Li+, choline, tris(hydroxymethyl)aminomethane, and glucosamine, all as Cl- salts, did not affect RVD. The anion pathway was unselective, since RVD was inhibited when NaCl was replaced by anion K+ salts with a permeability rank of SCN- = I- > NO3- > Cl- > benzoate > acetate >> SO3- > gluconate. RVD was unaffected by bumetanide (50 microM) and weakly inhibited by furosemide (2 mM). Quinidine but not other K+ channel blockers inhibited RVD, and its effect was reversed by gramicidin. RVD was inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and dipyridamole but not by diphenylamine-2-carboxylate or anthracene-9-carboxylate. These results suggest that diffusion possibly via channels rather than cotransporters is involved in the swelling-activated K+ and Cl- fluxes. Gramicidin did not change astrocyte volume in isosmotic conditions, but greatly accelerated RVD, suggesting that low Cl- permeability in isosmotic conditions markedly increases by swelling, thus making K+ permeability the rate-limiting step for RVD.

Circadian rhythmicity in the GABAergic system in the suprachiasmatic nuclei of the rat

The participation of GABAergic mechanisms in the regulation of circadian rhythmicity by the suprachiasmatic nuclei (SCN) has been suggested from different lines of evidence. Little is known, however, whether GABA synthesis, release, uptake or content within the SCN may show a circadian pattern. The present results show that the activity of the GABAergic system within the SCN region of the rat exhibits circadian rhythmicity, which is manifested by correlative changes of the GABA content and the glutamic acid decarboxylase activity under the light/dark cycle, and by changes in the GABA content in animals kept under constant darkness.

Inhibition of volume regulation and efflux of osmoregulatory amino acids by blockers of Cl- transport in cultured astrocytes

Regulatory volume decrease (RVD) in astrocytes was inhibited by the Cl- exchanger blockers 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), dipyridamole and niflumic acid but not by the Cl- channel inhibitors diphenylamine-2-carboxylate (DPC) and anthracene-9-carboxylate (9-AC). The volume activated efflux of [3H]taurine and [3H]D-aspartate (as marker for glutamate) was similarly affected by these compounds. However, neither RVD nor osmolyte fluxes were significantly reduced by removal of external Cl-, suggesting that an anion exchanger activity is not required for the volume regulatory process. Alternatively, these results suggest that the anion exchanger molecule may function as an unidirectional Cl- channel possibly permeable also to amino acids.

Contribution of organic and inorganic osmolytes to volume regulation in rat brain cells in culture

In this work we examined the time course and the amount released, by hyposmolarity, for the most abundant free amino acids (FAA) in rat brain cortex astrocytes and neurons in culture. The aim was to evaluate their contribution to the process of cell volume regulation. Taurine, glutamate, and D-aspartate in the two types of cells, beta-alanine in astrocytes and GABA in neurons were promptly released by hyposmolarity, reaching a maximum within 1-2 min. after an osmolarity change. A substantial amount of the intracellular pool of these amino acids was mobilized in response to hyposmolarity. The amount released in media with osmolarity reduced from 300 mOsm to 150 mOsm or 210 mOsm, represented 50%-65% and 13%-31%, respectively, of the total amino acid content in cells. In both astrocytes and neurons, the efflux of glutamine and alanine was higher under isosmotic conditions and increased only marginally during hyposmotic conditions. 86Rb+, used as tracer for K+, was released from astrocytes, 30% and 11%, respectively, in hyposmotic media of 150 mOsm or 210 mOsm but was not transported in neurons. From these results it was calculated that FAA contribute 54% and inorganic ions 46% to the process of volume regulation in astrocytes exposed to a 150 mOsm hyposmotic medium. This contribution was 55% for FAA and 45% for K+ and Cl- in cells exposed to 210 mOsm hyposmotic solutions. These results indicate that the contribution of FAA to the process of cell volume regulation is higher in astrocytes than in other cell types including renal and blood cells.

Cell volume regulation in cultured cerebellar granule neurons

Cultured rat cerebellar granule neurons exposed to solutions of reduced osmolarity, responded initially by swelling followed by a regulatory volume decrease (RVD) which is completed within 15 min. Increasing external osmolarity lead to cell shrinking but no evidence of volume regulation was observed within 1 hr. Replacing Na+ by choline did not affect RVD whereas N-methyl-D-glucamine accelerated the volume recovery and K+ suppressed it completely. The blockade of RVD in high extracellular K+ was only observed when chloride and nitrate but not sulfate or gluconate were the accompanying anions. Replacing intracellular Cl-, by long incubations with gluconate, markedly inhibited RVD. Removal of extracellular Ca2+ or addition of dantrolene which blocks Ca2+ released from intracellular stores had no effect on RVD. Increasing extracellular taurine prevented RVD. These results indicate that membrane permeability to K+, Cl-, and taurine is increased by hyposmolarity and suggest the involvement of these molecules in RVD in granule neurons.