Biomedical subjects

A M Silva

Publications and source records attributed to A M Silva.

At least 73 records · Page 4Linked to original sources

PubMed1993

Bursting electrical activity in pancreatic beta-cells: evidence that the channel underlying the burst is sensitive to Ca2+ influx through L-type Ca2+ channels.

In glucose-stimulated pancreatic beta-cells, the membrane potential alternates between a hyperpolarized silent phase and a depolarized phase with Ca2+ action potentials. The molecular and ionic mechanisms underlying these bursts of electrical activity remain unknown. We have observed that 10.2-12.8 mM Ca2+, 1 microM Bay K 8644 and 2 mM tetraethylammonium (TEA) trigger bursts of electrical activity and oscillations of intracellular free Ca2+ concentration ([Ca2+]i) in the presence of 100 microM tolbutamide. The [Ca2+]i was monitored from single islets of Langerhans using fura-2 microfluorescence techniques. Both the high-Ca(2+)- and Bay-K-8644-evoked [Ca2+]i oscillations overshot the [Ca2+]i recorded in tolbutamide. Nifedipine (10-20 microM) caused an immediate membrane hyperpolarization, which was followed by a slow depolarization to a level close to the burst active phase potential. The latter depolarization was accompanied by suppression of spiking activity. Exposure to high Ca2+ in the presence of nifedipine caused a steady depolarization of approximately 8 mV. Ionomycin (10 microM) caused membrane hyperpolarization in the presence of 7.7 mM Ca2+, which was not abolished by nifedipine. Charybdotoxin (CTX, 40-80 nM), TEA (2 mM) and quinine (200 microM) did not suppress the high-Ca(2+)-evoked bursts. It is concluded that: (1) the channel underlying the burst is sensitive to [Ca2+]i rises mediated by Ca2+ influx through L-type Ca2+ channels, (2) both the ATP-dependent K+ channel and the CTX- and TEA-sensitive Ca(2+)-dependent K+ channel are highly unlikely to provide the pacemaker current underlying the burst.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1993

[Mechanical reperfusion in acute myocardial infarction after failure of thrombolysis with intravenous streptokinase].

AIM: to report the clinical evolution of four patients with acute myocardial infarction that were subjected to immediate coronary angioplasty due to the failure of reperfusion with streptokinase. BACKGROUND: the limitations for the use of thrombolytic agents, an accepted treatment of acute myocardial infarction, or their uncertain results in selected groups of patients has prompted the search for mechanical revascularization infarction subjected to thrombolytic therapy with streptokinase (1.500.000 U i.v.) after administration of hydrocortisone (100 mg i.v.) and acetyl salicylic acid (500 mg od). After 60 min thrombolytic therapy and due to hemodynamic depression with requirement of inotropic agents or the absence of clinical signs of reperfusion, the patients were subjected to coronary angiography. In view of a total occlusion or severe stenosis of the artery responsible for the infarction, an immediate transluminal angiography was performed to improve coronary flow. RESULTS: transluminal coronary angioplasty revascularized arteries with total occlusion or increased the lumen of those with severe residual stenosis. This was accompanied by reduction in pain and hemodynamic improvement. In one patient with complete AV block, conduction was improved and sinus rhythm was recovered. Echocardiographic controls showed preservation of ventricular function with persistence of segmental motility alterations. CONCLUSIONS: transluminal coronary angioplasty can be a revascularization alternative in patients with acute myocardial infarction and failure of reperfusion with systemic streptokinase.

Aged↗

PubMed1993

[Percutaneous transluminal angioplasty in stenosis of Blalock-Taussig pulmonary systemic shunt in an adult patient].

AIM: The report of a female patient with tricuspid atresia and severe stenosis of the pulmonary artery, stenosis of the left pulmonary-systemic shunt and occlusion of the right systemic-pulmonary shunt. BACKGROUND: The use of transluminal angioplasty has been extended to the treatment of several congenital cardiopathies and, in some of them, it is the therapeutic procedure of choice. METHODS: Dilatation of the distal stenosis of the pulmonary-systemic shunt with a coaxial system composed initially by an 8 French right Judkins carrier catheter with a soft tip through which a 0.014" (0.036 cm) coronary angioplasty guidewire and 3 and 4 mm balloon catheters were advanced successively. Subsequently a 0.028" interchange Rosen guide was advanced, gradually introducing balloon catheters up to 8 mm of diameter. RESULTS: The dilatation with balloon catheter systems of increasing diameter allowed to amplify the stenosis zone, improving arterial oxygen partial pressure and saturation without evidences of left lung hyperflux. Considering the anatomic characteristics of the pulmonary systemic shunt, the use of carrier catheters facilitates the penetration of balloon catheters to the stenosis zone. CONCLUSION: Percutaneous transluminal angioplasty may be used with success in patients with stenosis of Blalock-Taussig shunts, independent of the anastomosis curvature and even if the magnitude of the stenosis is significant.

Adult↗

PubMed1992

High external Ca2+ levels trigger membrane potential oscillations in mouse pancreatic beta-cells during blockade of K(ATP) channels.

Glucose depolarizes the pancreatic beta-cell and induces membrane potential oscillations, but the nature of the underlying oscillatory conductance remains unknown. We have now investigated the effects of the Ca2+ ionophore ionomycin and high external Ca2+ concentration ([Ca2+]o) on glucose-induced electrical activity and whole islet intracellular free Ca2+ concentration ([Ca2+]i), under conditions where the K(ATP) channel was blocked (100 microM tolbutamide or 4 microM glibenclamide). Raising [Ca2+]o to 10.2 or 12.8 mM, but not to 5.1 or 7.7 mM, turned continuous electrical activity into bursting activity. High [Ca2+]o (12.8 mM) regenerated a pattern of fast [Ca2+]i oscillations overshooting the levels recorded in tolbutamide. Ionomycin (10 microM) raised the [Ca2+]i and synergized with 5.1 mM Ca2+ to hyperpolarize the beta-cell membrane. The data indicate that a [Ca2+]i-sensitive and sulphonylurea-insensitive oscillatory conductance underlies the beta-cell bursting activity.

Adenosine Triphosphate↗

PubMed1992

Ion channels in icosahedral virus: a comparative analysis of the structures and binding sites at their fivefold axes.

An analysis of the crystallographically determined structures of the icosahedral protein coats of Tomato Bushy Stunt Virus, Southern Bean Mosaic Virus, Satellite Tobacco Necrosis Virus, Human Rhinovirus 14 and Mengovirus around their fivefold axes is presented. Accessibilities surfaces, electrostatic energy profile calculations, ion-protein interaction energy calculations, free energy perturbation methods and comparisons with structures of chelating agents are used in this study. It is concluded that the structures built around the viral fivefold axes would be adequate for ion binding and transport. Relative ion preferences are derived for the binding sites, using free energy perturbation methods, which are consistent with the experimental data when available. In the cases where crystallographic studies determined the existence of ions on the fivefold axes, our results indicate that they would correspond to ions in crystallization or purification buffers. The environment of the fivefold axes are rich in polar residues in all icosahedral viral structures whose atomic coordinates are available, including some that are not being analyzed in detail in this work. The fivefold channel-like structures have most of the basic properties expected for real ion channels including a funnel at the entrance, a polar internal environment with frequent alternation of acidic and basic residues, ion binding sites, the capability to induce ion dehydration and ion transit from the external viral surface to the binding sites.

Capsid↗

PubMed1992

Kininogenase activity of rSMT3, a rat submandibular gland tonin.

rSMT3, a tonin like angiotensin II generating enzyme present in rSMG presents a potent oxytocic effect on the isolated rat uterus, which was blocked by a B2 bradykinin receptor antagonist. Under optimal conditions of pH, rSMT3 liberates kinin at rate 19-fold greater than angiotensin II.

Angiotensin II↗

PubMed1992

[Angiographic findings in non-Q wave infarction and their relation to ST-T changes].

Non q wave myocardial infarction has been attributed to occlusion of a vessel with no ECG representation, early reperfusion of the occluded artery or occlusion of a vessel with generous collateral flow. The coronary arteriography of 84 patients with non Q wave myocardial infarction performed at 16 + 17 (SD) days after infarction was analyzed. Main left lesion was found in 6 (17%), single vessel disease in 30 (36%), two vessel disease in 18 (24%) and 3 vessel disease in 16 (19%). The "culprit" vessel had a critical residual lesion in 38 patients (45%): 22 affected the left anterior descending artery, 10 the circumflex, and 5 the right coronary artery. No residual lesion was found in 10 patients (12%). An occluded artery was found in 32 patients (38%): circumflex in 20, right coronary artery in 9 and left anterior descending in 3 (p < 0.01). Significant collateral flow to the occluded vessel was present in 41% of cases. The ST segment was analyzed in 82 patients. Depression of ST was found in 29 (35%), elevation in 22 (27%), negative T waves in 17 (21%) and minimal alterations in 17%. There was no correlation between ST levels and coronary occlusion of the culprit artery. Depression of ST was more commonly (p < 0.01) associated with severe coronary artery disease (main left or 3 vessel disease), which may be related to the poorer prognosis in these cases.

Adult↗

PubMed1991

Vitamins B1 and B6 tubular electrodes as FIA detectors; their use in the analysis of pharmaceutical products.

Ion-selective electrodes without an inner reference solution and tubular potentiometric detectors for the determination of vitamins B1 and B6 in pharmaceutical preparations by flow injection analysis (FIA) are reported. The membranes were prepared with the vitamin tetra(2-chlorophenyl)borate (TCPB) dissolved in o-nitrophenyloctyl ether (o-NPOE) and immobilized on PVC. Intrinsic behaviour of the tubular detectors was assessed using a low-dispersion single-channel FIA manifold and was compared with conventionally-shaped electrodes using the same membrane. Data obtained in the determination of vitamins B1 and B6 in pharmaceutical preparations with a double channel flow injection manifold incorporating the tubular detectors are presented and compared with those obtained by the U.S. Pharmacopeia method and by direct potentiometry with conventionally-shaped electrodes.

Electrodes↗

PubMed1991

SISCOPE: a multiuser information system for gastrointestinal endoscopy.

SISCOPE is an integrated data management system for use in gastrointestinal endoscopy units which operates in the multiuser mode on UNIX minicomputers or MS-DOS personal computers and can be used for patient bookings, endoscopic data entry and retrieval, and automatic report generation in upper gastrointestinal endoscopy, proctologic examinations, colonoscopy and peritoneoscopy. The description of endoscopic findings is remarkably detailed and data entry very rapid due to an advanced design of input screens that incorporates several recent concepts, including windows, menu bars and pull-down menus; typing is eliminated as data is entered with a mouse by pointing at options within menus. Endoscopic findings can be described under eight headings: morphology, topography, qualifiers, modifiers, signs of bleeding, endoscopic diagnosis, pathological diagnosis and etiology. Terminology is based strictly 3on the OMED system. SISCOPE also allows recording of details on endoscopic procedures, indications for the examination, preparation, premedication, complications and late entry of pathology reports. After entering all data, a report in natural language is produced automatically, the entire process taking one minute on average. Data retrieval programs give on-line access to previous examinations of a given patient and automatically generate activity reports. A formal language allows direct queries to the database and transfer of data for statistical analysis or other data processing. The system is simple to learn and use because operation is intuitive and all endoscopic techniques share the same basic menu structure and screen design.

Computer Systems↗

PubMed1991

Acute fatal Trypanosoma cruzi meningoencephalitis in a human immunodeficiency virus-positive hemophiliac patient.

A 37-year-old hemophiliac patient with known, asymptomatic human immunodeficiency virus infection and chronic Chagas' disease was admitted to the hospital complaining of fever and headache. A computed tomographic scan revealed multiple ring-enhancing lesions in both cerebral hemispheres. No antibodies to Trypanosoma cruzi were found in the cerebrospinal fluid. Treatment for toxoplasmosis of the central nervous system, which was considered the most likely diagnosis, was instituted, but the patient died after progressive neurologic deterioration. An autopsy revealed severe meningoencephalitis caused by T. cruzi.

Acute Disease↗

PubMed1991

[Myocardial ischemia in patients older than 70 years of age. Clinical and angiographic aspects].

We studied 77 patients with clinical suspicion of ischemic heart disease whose age ranged from 70 to 84 years. Patients with atypical angina had mostly normal coronary arteries, while those with unstable angina usually had three vessel disease or main left disease. According to the left ventricular function, surgery was considered safe in 66% of patients with unstable angina and 33% of those with stable angina. One patient developed a pseudoaneurysm at the arterial puncture site and hematomas were present in 3 other patients. Currently we try to avoid coronary arteriography in older patients with atypical angina due to its low yield.

Age Factors↗

PubMed1989

IgG subclasses responsible for immune clearance in mice infected with Trypanosoma cruzi.

To examine the role of different immunoglobulin subclasses in the immune clearance of Trypanosoma cruzi, mice containing bloodstream trypomastigotes were injected intravenously with immune serum, IgG-depleted serum, or with the IgG1 or IgG2 fractions and the rate of removal of the parasites from circulation was determined. Using IgG concentrations similar to those found in the immune serum, the rate of clearance mediated by IgG2 was six-fold higher than that obtained with IgG1. This difference did not appear to be due to differences in antibody specificity, as Western blotting showed that each isotype recognized a similar set of antigens extracted from the parasite. However, the T. cruzi specific antibody content of the IgG2 was approximately five-fold higher than IgG1. When the dose of IgG was adjusted to equalize the antibody content, the clearance ability of the IgG1 and IgG2 was very similar. It is concluded that the two subclasses have a similar clearance ability.

Animals↗

PubMed1988

Multiple sclerosis with early childhood onset. A case report.

A 2 year old boy was admitted owing to a subacute episode of ataxic gait and hearing deficit. Computerized tomography (CT) was normal and cerebrospinal fluid (CSF) analysis revealed gamma globulins level of 15.4% (normal 7 to 14%). There was spontaneous remission after 7 months. At 5 years of age the boy incurred a second episode with predominantly right appendicular ataxia and tonic gaze deviation to the right side. CT showed a low-density lesion in the white matter adjacent to the right frontal horn. Visual and auditory evoked potentials were abnormal. CSF revealed a mild increase in gamma globulins level of 14.5% with an abnormal T lymphocyte subsets study. The combination of visual, cerebellar, brain stem and paraventricular lesions with clear remissions and exacerbations, supported by CT, CSF and evoked potentials findings suggests the diagnosis of multiple sclerosis even at this early age.

Age Factors↗

PubMed1987

Refined structure of southern bean mosaic virus at 2.9 A resolution.

The T = 3 capsid of southern bean mosaic virus is analyzed in detail. The beta-sheets of the beta-barrel folding motif that form the subunits show a high degree of twist, generated by several beta-bulges. Only 34 water molecules were identified in association with the three quasi-equivalent subunits, most of them on the external viral surface. Subunit contacts related by quasi-3-fold axes are similar, are dominated by polar interactions and have almost identical calcium binding sites. There is no metal ion on the quasi-3-fold axis, as previously reported. Subunits related by quasi-2-fold and icosahedral 2-fold axes have different contacts but nevertheless display almost identical interactions between the antiparallel helices alpha A. A dipole-dipole type interaction between these helices may produce an energetically stable hinge that allows two types of dimers in a T = 3 assembly. The temperature factor distribution, the hydrogen-bonding pattern, and the contacts across the icosahedral 2-fold axes suggest that one of the dimer types is present in the intact virion and probably also in solution; the other is produced only during capsid assembly. Interactions along the 5-fold axes are mainly polar and possibly form an ion channel. The beta-sheet structures of the three subunits can be superimposed with considerable precision. Significant relative distortions between quasi-equivalent subunits occur mainly in helices and loops. The two dimeric forms and the subunit distortions are the consequence of the non-equivalent subunit environments in the capsid.

Amino Acid Sequence↗

PubMed1987

Acquisition of thermotolerance during development of Blastocladiella emersonii.

In the fungus Blastocladiella emersonii the synthesis of heat-shock proteins is developmentally regulated; particular subsets of heat-shock proteins are induced by heat shock during sporulation, germination and growth and some heat shock-related proteins are spontaneously expressed during sporulation (Bonato et al., 1987, Eur. J. Biochem., in press). Nevertheless, acquisition of thermotolerance can be induced at any stage of the life cycle. The development of thermotolerance is correlated with the enhanced synthesis of some heat-shock proteins: hsp 82a, hsp 82b, hsp 76, hsp 70, hsp 60, hsp 25, hsp 17b. Other hsps are not specifically involved in thermotolerance.

Adaptation, Physiological↗

PubMed1987

Differential expression of heat-shock proteins and spontaneous synthesis of HSP70 during the life cycle of Blastocladiella emersonii.

The heat-shock response in Blastocladiella emersonii is dependent on the developmental stage. Cells exposed to elevated temperatures at different stages of the life cycle (sporulation, germination or growth) show a differential synthesis of heat-shock proteins (hsps). Of a total of 22 polypeptides induced, particular subsets of hsps appear in each phase, demonstrating a non-coordinate heat-shock gene expression. In contrast, heat-shock-related proteins (hsp76, hsp70, hsp39a) are spontaneously expressed at a high level during sporulation. By the criteria of two-dimensional gel electrophoresis and partial proteolysis mapping, the 70,000-Da protein, whose synthesis is induced spontaneously during sporulation, is indistinguishable from the heat-inducible hsp70. The techniques of in vitro translation, and Northern analysis using a Drosophila hsp70 probe, demonstrated that enhanced synthesis of hsp70, which occurs during heat-shock treatment and spontaneously during sporulation, is associated with an accumulation of hsp70 mRNA. These observations suggest that hsp70 gene expression is induced during sporulation.

Blastocladiella↗

PubMed1987

Changes in the pattern of protein synthesis during zoospore germination in Blastocladiella emersonii.

Using two-dimensional gel electrophoresis, we analyzed the pattern of proteins synthesized during Blastocladiella emersonii zoospore germination in an inorganic solution, in both the presence and absence of actinomycin D. During the transition from zoospore to round cells (the first 25 min), essentially no qualitative differences were noticeable, indicating that the earliest stages of germination are entirely preprogrammed with stored RNA. Later in germination (after 25 min), however, changes in the pattern of protein synthesis were found. Some of these proteins (a total of 6 polypeptides) correspond possibly to a selective translation of stored messages, whereas the majority of the changed proteins (22 polypeptides) corresponds to newly synthesized mRNA. Thus, multiple levels of protein synthesis regulation seem to occur during zoospore germination, involving both transcriptional and translational controls. We also analyzed the pattern of protein synthesis during germination in a nutrient medium; synthesis of specific polypeptides occurred during late germination. During early germination posttranslational control was also observed, several labeled proteins from zoospores being specifically degraded or charge modified.

Blastocladiella↗

PubMed1986

Heat shock protein synthesis during development in Caulobacter crescentus.

Caulobacter crescentus cells respond to a sudden increase in temperature by transiently inducing the synthesis of several polypeptides. Two of the proteins induced, Hsp62 and Hsp70, were shown to be analogous to the heat shock proteins of Escherichia coli, GroEL and DnaK, respectively, by immunological cross-reactivity with antibodies raised against the E. coli proteins. Two-dimensional gel electrophoretic resolution of extracts of cells labeled with [35S]methionine during heat shock led to the identification of 20 distinct Hsps in C. crescentus which are coordinately expressed, in response to heat, at the various stages of the cell division cycle. Thus, a developmental control does not seem to be superimposed on the transient activation of the heat shock genes. Nonetheless, under normal temperature conditions, four Hsps (Hsp70, Hsp62, Hsp24b, and Hsp23a) were shown to be synthesized, and their synthesis was cell cycle regulated.

Bacterial Proteins↗