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E Rojas

Publications and source records attributed to E Rojas.

At least 55 records · Page 3Linked to original sources
PubMed1998

Drug use pathways among high school students of Mexico.

OBJECTIVE: This study surveyed high school student drug users in urban areas of Mexico to describe use patterns and drug-related behaviors among adolescents and to develop predictor models of pathways to underage drug use. SUBJECT/DESIGN: A National School Survey was conducted among high school students where data are provided by the State. Only urban sites were considered for this study (n = 40,521). Stratified two-stage cluster sampling was used; schools and groups within the schools were the sampling units. CONCLUSIONS: Male adolescents who have worked the previous year, have high exposure within the family and are affiliated with drug using peers are at increased risk of becoming drug users and subject to depression and suicidal ideation as well as drug-related social problems.

Adolescent↗
PubMed1998

Regulation of KCa current by store-operated Ca2+ influx depends on internal Ca2+ release in HSG cells.

This study examines the Ca2+ influx-dependent regulation of the Ca2+-activated K+ channel (KCa) in human submandibular gland (HSG) cells. Carbachol (CCh) induced sustained increases in the KCa current and cytosolic Ca2+ concentration ([Ca2+]i), which were prevented by loading cells with 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid (BAPTA). Removal of extracellular Ca2+ and addition of La3+ or Gd3+, but not Zn2+, inhibited the increases in KCa current and [Ca2+]i. Ca2+ influx during refill (i.e., addition of Ca2+ to cells treated with CCh and then atropine in Ca2+-free medium) failed to evoke increases in the KCa current but achieved internal Ca2+ store refill. When refill was prevented by thapsigargin, Ca2+ readdition induced rapid activation of KCa. These data provide further evidence that intracellular Ca2+ accumulation provides tight buffering of [Ca2+]i at the site of Ca2+ influx (H. Mogami, K. Nakano, A. V. Tepikin, and O. H. Petersen. Cell 88: 49-55, 1997). We suggest that the Ca2+ influx-dependent regulation of the sustained KCa current in CCh-stimulated HSG cells is mediated by the uptake of Ca2+ into the internal Ca2+ store and release via the inositol 1,4,5-trisphosphate-sensitive channel.

Atropine↗
PubMed1998

Antisocial behavior: its relation to selected sociodemographic variables and alcohol and drug use among Mexican students.

This study is part of the National School Survey on drug use by high school students in Mexico. The validity, reliability, and results of the Antisocial Acts Scale in Mexico City (n = 3,501) are discussed. Using factorial analyses of the Antisocial Acts Scale, two major sources of variability were observed. The first one is related to antisocial acts with severe social consequences, in which violence and drug selling are included, and the second one is related to thefts. Significant differences were found in the number of offenses among groups of different gender, age, and occupation during the previous year. More antisocial acts were perpetrated by alcohol and drug users than by nonusers. In a logistic regression model, it was found that the main risk factors for perpetrating antisocial acts were being male, using alcohol, and using other drugs.

Adolescent↗
PubMed1997

Induction of p53 protein expression by sodium arsenite.

Arsenic is carcinogen for humans and has been shown to act as an enhancer in initiated animal models. In a previous work we found impairment of lymphocyte proliferation in arsenic-exposed individuals and in vitro we obtained dose-related inhibition of mitotic response and lymphocyte proliferation. Intrigued by these effects and based on the role of p53 on cell proliferation, we tested different concentrations of sodium arsenite for their ability to induce the expression of tumor suppressor gene p53 in different cell lines (HeLa, C-33A. Jurkat) and a lymphoblast cell line transformed with Epstein-Barr virus (LCL-EBV). We also evaluated changes in their viability after 24 h arsenic treatment; C-33A cells showed the higher sensitivity to arsenic treatment while HeLa, Jurkat and LCL-EBV cells showed similar cytotoxicity curves. Immunoblots showed an increased expression of p53 gene with 1 microM sodium arsenite in Jurkat cells and 10 microM sodium arsenite in HeLa and LCL-EBV cells. In addition, we transfected Jurkat cells and human lymphocytes with wild-type and mutated p53 genes; lymphocytes and Jurkat cells that received the mutated p53 showed increased sensitivity to arsenic cytotoxicity. Data obtained indicate that arsenic induces p53 expression and that cells with a functional p53 contend better with damage induced by this metalloid.

Arsenites↗
PubMed1997

A9 fibroblasts transfected with the m3 muscarinic receptor clone express a Ca2+ channel activated by carbachol, GTP and GDP.

Muscarinic m3 receptor-mediated changes in cytosolic Ca2+ concentration ([Ca2+]i) occur by activation of Ca2+ release channels present in the endoplasmic reticulum membrane and Ca2+ entry pathways across the plasma membrane. In this report we demonstrate the coupling of m3 muscarinic receptors to the activation of a voltage-insensitive, cation-selective channel of low conductance (3.2 +/- 0.6 pS; 25 mM Ca2+ as charge carrier) in a fibroblast cell line expressing m3 muscarinic receptor clone (A9m3 cells). Carbachol (CCh)-induced activation of the cation-selective channel occurred both in whole cell and excised membrane patches (CCh on the external side), suggesting that the underlying mechanism involves receptor-channel coupling independent of intracellular messengers. In excised inside-out membrane patches from nonstimulated A9m3 cells GTP (10 microM) and GDP (10 microM) activated cation-selective channels with conductances of approximately 4.3 and 3.3 pS, (25 mM Ca2+ as charge carrier) respectively. In contrast, ATP (10 microM), UTP (10 microM) or CTP (10 microM) failed to activate the channel. Taken together, these results suggest that carbachol and guanine nucleotides regulate the activation of a cation channel that conducts calcium.

Animals↗
PubMed1997

Evidence that calcium release-activated current mediates the biphasic electrical activity of mouse pancreatic beta-cells.

The electrical response of pancreatic beta-cells to step increases in glucose concentration is biphasic, consisting of a prolonged depolarization with action potentials (Phase 1) followed by membrane potential oscillations known as bursts. We have proposed that the Phase 1 response results from the combined depolarizing influences of potassium channel closure and an inward, nonselective cation current (ICRAN) that activates as intracellular calcium stores empty during exposure to basal glucose (Bertram et al., 1995). The stores refill during Phase 1, deactivating ICRAN and allowing steady-state bursting to commence. We support this hypothesis with additional simulations and experimental results indicating that Phase 1 duration is sensitive to the filling state of intracellular calcium stores. First, the duration of the Phase 1 transient increases with duration of prior exposure to basal (2.8 mM) glucose, reflecting the increased time required to fill calcium stores that have been emptying for longer periods. Second, Phase 1 duration is reduced when islets are exposed to elevated K+ to refill calcium stores in the presence of basal glucose. Third, when extracellular calcium is removed during the basal glucose exposure to reduce calcium influx into the stores, Phase 1 duration increases. Finally, no Phase 1 is observed following hyperpolarization of the beta-cell membrane with diazoxide in the continued presence of 11 mm glucose, a condition in which intracellular calcium stores remain full. Application of carbachol to empty calcium stores during basal glucose exposure did not increase Phase 1 duration as the model predicts. Despite this discrepancy, the good agreement between most of the experimental results and the model predictions provides evidence that a calcium release-activated current mediates the Phase 1 electrical response of the pancreatic beta-cell.

Animals↗
PubMed1997

Effects of Cuban red propolis on galactosamine-induced hepatitis in rats.

Using transmission electron microscopy and biochemical analysis, the effect of cuban red propolis against hepatitis induced by 1,000 mg kg-1 of galactosamine in rats was studied. An ethanolic extract of propolis was prepared and it was given to rats at doses of 10, 50 and 100 mg kg-1, 30 min before the hepatotoxin. Propolis extract prevented hepatocytes alterations induced by galactosamine. It was mainly seen in rough endoplasmic reticulum, Golgi complex, nucleus and plasma membrane of hepatocytes. Propolis extract induced reversion of the increased activity of alanine aminotransferase and malondialdehyde concentration in the serum of rats treated with galactosamine. The probable role of antioxidant activity of propolis in the prevention of hepatitis is discussed in this paper.

Administration, Oral↗
PubMed1997

Alzheimer's disease amyloid beta-protein forms Zn(2+)-sensitive, cation-selective channels across excised membrane patches from hypothalamic neurons.

We have previously shown that the 40-residue peptide termed amyloid beta-protein (A beta P[1-40]) in solution forms cation-selective channels across artificial phospholipid bilayer membranes. To determine whether A beta P[1-40] also forms channels across natural membranes, we used electrically silent excised membrane patches from a cell line derived from hypothalamic gonadotrophin-releasing hormone GnRH neurons. We found that exposing either the internal or the external side of excised membrane patches to A beta P[1-40] leads to the spontaneous formation of cation-selective channels. With Cs+ as the main cation in both the external as well as the internal saline, the amplitude of the A beta P[1-40] channel currents was found to follow the Cs+ gradient and to exhibit spontaneous conductance changes over a wide range (50-500 pS). We also found that free zinc (Zn2+), reported to bind to amyloid beta-protein in solution, can block the flow of Cs+ through the A beta P[1-40] channel. Because the Zn2+ chelator o-phenanthroline can reverse this blockade, we conclude that the underlying mechanism involves a direct interaction between the transition element Zn2+ and sites in the A beta P[1-40] channel pore. These properties of the A beta P[1-40] channel are rather similar to those observed in the artificial bilayer system. We also show here, by immunocytochemical confocal microscopy, that amyloid beta-protein molecules form deposits closely associated with the plasma membrane of a substantial fraction of the GnRH neurons. Taken together, these results suggest that the interactions between amyloid beta-protein and neuronal membranes also occur in vivo, lending further support to the idea that A beta P[1-40] channel formation might be a mechanism of amyloid beta-protein neurotoxicity.

Amyloid beta-Peptides↗
PubMed1997

Deprivation of Na+, Ca2+ and Mg2+ from the extracellular solution increases cytosolic Ca2+ and stimulates catecholamine secretion from cultured bovine adrenal chromaffin cells.

We report here that exposing cultured chromaffin cells to a low ionic strength medium (with sucrose in place of NaCl to maintain osmolarity) can induce a marked elevation in cytosolic Ca2+ concentration ([Ca2+]i) and catecholamine (CA) release. To determine the underlying mechanism, we first studied the effects of low [Na+]o on single cell [Ca2+]i (using fluo-3 as Ca2+ indicator) and CA release from many cells. In a Mg2+ and Ca2+-deficient medium, lowering the external concentration of Na2+ ([Na+]o) evoked CA secretion preceded by a transitory [Ca2+]i rise, the amplitude of which was inversely related to [Na+]o. By contrast, in the presence of either [Ca2+]o (2 mM) and [Mg2+]o (1.4 mM) or [Mg2+]o alone (3.4 mM), lowering the ionic strength was without effect. Furthermore, in a physiologic [Na+]o, [Ca2+]o and [Mg2+]o medium, two or three consecutive applications of the cholinergic agonist oxotremorine-M (oxo-M) consistently evoked a substantial [Ca2+]i, rise. By contrast, consecutive applications of oxo-M in a Ca2+-deficient medium failed to evoke a rise in [Ca2+]i after the first exposure to the agonist. To clarify the underlying mechanism, we measured and compared the effects of low [Na+]o and the cholinergic agonists nicotine and oxo-M on changes in [Ca2+]i; we studied the effects of these agonists on both membrane potential, Vm (under current clamp conditions), and [Ca2+]i by single cell microfluorimetry (indo-1 as Ca2+ indicator). We observed that, in the presence of [Ca2+]o and [Mg2+]o, lowering [Na+]o had no effect on Vm. In a Ca2+-deficient medium, lowering [Na+]o depolarized the membrane from ca. -60 to -10 mV. As expected, we found that nicotine (10 microM) depolarized the membrane (from ca. -60 to -20 mV) and simultaneously evoked a substantial [Ca2+]i rise that was [Ca2+]o-dependent. However, contrary to our expectations, we found that the muscarinic agonist oxo-M (50 microM) also depolarized the membrane and induced an elevation in [Ca2+]i. Furthermore, both signals were blocked by D-tubocurarine, insinuating the nicotinic character of oxo-M in adrenal chromaffin cells from bovine. These results suggest that both nicotine and oxo-M stimulate Ca2+ entry, probably through voltage-gated Ca2+-channels. We also show here that oxo-M (and not low [Na+]o) stimulates phosphoinositide turnover.

Adrenal Medulla↗
PubMed1997

A novel calcium-activated apamin-insensitive potassium current in pituitary gonadotrophs.

In cultured rat pituitary gonadotrophs, GnRH-induced oscillations in cytosolic calcium concentration ([Ca2+]i) are associated with periodic membrane hyperpolarization. The hyperpolarizing waves are secondary to the activation of apamin-sensitive Ca2+-activated K+ channels that account for a single class of 125I-apamin binding sites present in these cells. In a substantial fraction of gonadotrophs, however, we observed a Ca2+-controlled oscillatory current that was resistant to apamin, even at concentrations five orders of magnitude higher than the dissociation constant (Kd) observed in the binding experiments. With the K+ in the pipette, the apamin-resistant current showed a reversal potential of -42 mV, nearly 40 mV more positive than that of the apamin-sensitive current. With Cs+ in place of K+ in the pipette solution, both the size of the apamin-insensitive current and its reversal potential remained unchanged. Ion substitution studies further revealed that the reversal potential was independent of Cl-. In contrast, an 11 mV hyperpolarizing shift in the reversal potential occurred when extracellular Na+ was reduced to 80 mM. In cells expressing apamin-resistant conductances, addition of apamin evoked a marked increase in the duration of the action potentials and reduction in the frequency of spontaneous spiking. In the presence of GnRH, gonadotrophs exhibit the typical burst pattern of electrical activity. Further exposure of the cells to apamin depolarized the membrane from a silent phase bursting level of about -80 mV to a new level of about -40 mV. These observations indicate that, in addition to apamin-sensitive current, a subpopulation of pituitary gonadotrophs also expresses a cationic component of the Ca2+-activated membrane conductance that has the potential to remodulate spontaneous and agonist-induced electrical activity.

Animals↗
PubMed1997

DNA damage in leukocytes and buccal and nasal epithelial cells of individuals exposed to air pollution in Mexico City.

There is an increased interest in using biological markers to monitor individuals for possible exposure to environmental toxicants. Test systems which permit the sensitive detection of DNA damage and DNA repair are critically important in such studies. The single cell gel electrophoresis (SCG) assay is a rapid and a sensitive method for the evaluation of DNA damage at the single cell level, providing information on the occurrence of DNA single-strand breaks and alkali labile sites using alkaline conditions. In this study, the differences in the basal level of DNA damage between young adults from the south (exposed principally to high levels of ozone) and young adults from the north (exposed principally to hydrocarbons and particles) of Mexico City were investigated by the SCG assay using three different cell types (leukocytes and nasal and buccal epithelial cells). We found an increased DNA migration in blood leukocytes and nasal cells from individuals who live in the southern part of the city compared to those living in the northern part; however, no differences were observed for buccal epithelial cells. These results show the feasability of using the SCG assay to evaluate DNA damage in different tissues and its great potential for use in the monitoring of humans potentially exposed to genotoxic pollutants.

Adult↗
PubMed1996

A complete genome screen for genes predisposing to severe bipolar disorder in two Costa Rican pedigrees.

Bipolar mood disorder (BP) is a debilitating syndrome characterized by episodes of mania and depression. We designed a multistage study to detect all major loci predisposing to severe BP (termed BP-I) in two pedigrees drawn from the Central Valley of Costa Rica, where the population is largely descended from a few founders in the 16th-18th centuries. We considered only individuals with BP-I as affected and screened the genome for linkage with 473 microsatellite markers. We used a model for linkage analysis that incorporated a high phenocopy rate and a conservative estimate of penetrance. Our goal in this study was not to establish definitive linkage but rather to detect all regions possibly harboring major genes for BP-I in these pedigrees. To facilitate this aim, we evaluated the degree to which markers that were informative in our data set provided coverage of each genome region; we estimate that at least 94% of the genome has been covered, at a predesignated threshold determined through prior linkage simulation analyses. We report here the results of our genome screen for BP-I loci and indicate several regions that merit further study, including segments in 18q, 18p, and 11p, in which suggestive lod scores were observed for two or more contiguous markers. Isolated lod scores that exceeded our thresholds in one or both families also occurred on chromosomes 1, 2, 3, 4, 5, 7, 13, 15, 16, and 17. Interesting regions highlighted in this genome screen will be followed up using linkage disequilibrium (LD) methods.

Bipolar Disorder↗
PubMed1996

Effect of hydroxyurea and normal plasma on DNA synthesis in lymphocytes from Fanconi anemia patients.

Fanconi anemia (FA) is characterized at the cellular level by a high frequency of spontaneous chromosomal aberrations; crosslinking agents cause an abnormal increase in the frequency of chromosomal damage, and semiconservative DNA synthesis is severely inhibited. Deoxyribonucleotides are needed in both semiconservative and repair DNA synthesis. To investigate the involvement of deoxyribonucleotide pools in the inhibition of DNA synthesis in FA, we evaluated the effect on FA lymphocytes of hydroxyurea (HU), an inhibitor of ribonucleotide reductase which is known to alter the intracellular levels of deoxyribonucleotides. To achieve this goal, lymphocyte cultures of 4 FA patients and 4 normal individuals were used. Cultures were treated with HU and/or mitomycin C and normal human plasma. All cultures were processed to detect the number of DNA synthesizing nuclei by autoradiography. Scoring of 2000 nuclei for each kind of culture every 6 h in the last 24 h of incubation showed that, in long incubation periods, DNA synthesis in FA is largely inhibited by HU and this hypersensitivity may be partially decreased by addition of normal human plasma. It is known that recovery from damage induced by HU involves several enzymes such as flavin oxido-reductase, superoxide dismutase and catalase which are involved in the production or scavenging of O2 radicals; FA cells are deficient in the detoxification of oxygen and this could explain the response of FA cells to HU.

Cells, Cultured↗
PubMed1996

DNA damage in exfoliated buccal cells of smokers assessed by the single cell gel electrophoresis assay.

The alkaline single-cell gel electrophoresis assay or comet assay is a sensitive and rapid method for DNA strand breaks and detection of alkali labile sites at the single cell level, it further provides information on the presence of damage among individual cells. In this paper we explore the use of this technique utilizing exfoliated buccal mucosa cells from non-smokers (9 donors) and smokers (11 donors). The extent of DNA image length was found to be significantly increased in the smoker group (89.30 +/- 16.18 microns) than in the non-smoker group (52.01 +/- 10.43 microns). Our results indicate that the single-cell gel electrophoresis assay could be applied to human monitoring using exfoliated buccal epithelial cells.

Adult↗
PubMed1996

A rise in nuclear calcium translocates annexins IV and V to the nuclear envelope.

Following incubation of human fibroblasts with Ca2+ ionophore A23187, we found strong immunofluorescence labelling of the nuclear envelope by annexin IV antibody. Using confocal imaging of cells loaded with Fluo-3, we showed that A23187 generates an intense and sustained rise of Ca2+ in the nucleus. By contrast, stimulation without extracellular Ca2+ produces only a brief rise in nuclear Ca2+ that does not promote annexin IV translocation to the nuclear envelope, and compounds that induce only a transient increase of nuclear Ca2+ do not support translocation of annexin IV. In addition, annexin V was also translocated to the nuclear envelope by A23187, but distribution of annexins I, II, VI and VII is unaffected. In in vitro assays with isolated nuclei, annexin V was also found to bind to the nuclear envelope in a Ca2+-dependent manner. These results demonstrate that the translocation to the nuclear envelope of different types of Ca2+-regulated proteins is directly triggered by a major rise of Ca2+ in the nucleus.

Animals↗
PubMed1996

Genotoxic effects of bistratene A on human lymphocytes.

Bistratene A, a toxin isolated from the colonial ascidian Lissoclinum bistratum causes a decrease in mitotic index and retardation of lymphocyte proliferation kinetics when it is added at 48 h to 72-h human lymphocyte cultures. In the same cultures, the incidence of sister chromatid exchanges was not altered by this compound. We also observed an increase in the number of polyploid cells in the cultures, and alterations of the beta-tubulin organization by immunocytochemistry with an antibody against beta-tubulin. Bistratene A induces DNA damage in a dose-dependent fashion in leukocytes, as measured by the alkaline single cell gel electrophoresis assay. These results show that bistratene A interferes with microtubule assembly, is cytotoxic and cytostatic, and that it causes DNA damage.

Acetamides↗