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Biomedical subjects

L Rojas

Publications and source records attributed to L Rojas.

At least 19 recordsLinked to original sources

Development of a pediatric liver transplantation program in Argentina.

This article describes the preliminary experimental steps and clinical implementation of a purely pediatric liver transplantation (LT) program in a large public children's hospital in Buenos Aires, Argentina, a city with well over 10 million inhabitants and a referral population of over 30 million. Between 1993 and 1997, 84 LTs were performed in 81 patients, of which one-fourth weighed below 10 kg. The main indications were biliary atresia (n = 25, 30%) and fulminant liver failure (n = 23, 27%), followed by autoimmune cirrhosis (n = 14, 16%) and other liver diseases. Shortage of organs due to local conditions led to the use of liver-reduction techniques in 48 cases (57%), split liver in 2, and living-related donor (LRD) in 2. Retransplantation was necessary in 3 instances. Seventy-eight percent of the recipients survived for more than 1 year and 71% were alive after 4 years. The authors comment on the need for adaptation to local conditioning factors when developing a pediatric LT program in any country in which demographics and economic, medical, and sociological environments have a decisive influence on organ procurement, the actual performance of the operation, and the lifelong postoperative medication. In Buenos Aires, where the hospital setting is well-developed, the indications are in part determined by the high incidence of hepatitis A. Organ shortages in our area led to liberal use of liver reduction, split-liver, and LRD techniques. The overall results of the first years of such a program were largely satisfactory.

Argentina

Venezuelan hemorrhagic fever: clinical and epidemiological studies of 165 cases.

Epidemiological and clinical data are presented on 165 cases of Venezuelan hemorrhagic fever (VHF), a newly emerging viral zoonosis caused by Guanarito virus (of the family Arenaviridae). The disease is endemic in a relatively circumscribed area of central Venezuela. Since its first recognition in 1989, the incidence of VHF has peaked each year between November and January, during the period of major agricultural activity in the region of endemicity. The majority of cases have involved male agricultural workers. Principal symptoms among the patients with VHF included fever, malaise, headache, arthralgia, sore throat, vomiting, abdominal pain, diarrhea, convulsions, and a variety of hemorrhagic manifestations. The majority of patients also had leukopenia and thrombocytopenia. The overall fatality rate among the 165 cases was 33.3%, despite hospitalization and vigorous supportive care.

Hemorrhagic Fevers, Viral

Action of protein kinase A activators on the caudal neuromuscular junction of toad tadpoles, recorded on synaptic spots.

Miniature end-plate currents (MEPCS), from synaptic spots on the caudal muscles of Bufo marinus tadpoles, were analyzed in both pre- and postsynaptic domains, when protein kinase A (PKA) activity modificators were used. Sp-cAMPS diasteromer induced an increase in MEPC frequency, which was completely reversed by Rp-cAMPS. However, changes in the decay time of MEPCS were not detected. Dibutyryl-cAMP produced a similar presynaptic action, but its postsynaptic action was similar to butyrate. Presynaptic effect of forskolin (FSK), if any, is masked by the increase of MEPC frequency produced by dimethylsulfoxide (DMSO), the solvent used.

Administration, Topical

An empirical study of the psychodynamics of suicide: a preliminary report.

Preliminary results from a study of psychodynamic constructs are presented based on data from inpatients following a suicide attempt. The study examines the association between four psychodynamic constructs, severity of suicidal intent, and severity of depressive symptomatology in a sample of hospitalized suicide attempters. Higher levels of suicidal intent were associated with less differentiated self and object representations and less emotional investment in relationships. More severe depressive symptoms in suicide attempters were correlated with more self-targeted anger, less eternally directed anger, higher levels of shame and guilt, more affectively negative views of relationships, greater use of maladaptive and self-sacrificing defenses, and more impaired reality testing. These findings offer some preliminary empirical support for the validity of psychodynamic theories of suicidal behavior.

Adult

The role of pulse oximetry. Its use as an indicator of severe respiratory disease in Peruvian children living at sea level. Respiratory Group in Peru.

OBJECTIVE: To evaluate pulse oximetry as a technique for diagnosing pneumonic and nonpneumonic acute lower respiratory tract infection (ALRI) in Peruvian children. DESIGN: Children with acute respiratory infection were diagnosed with hypoxemia by pulse oximetry, with ALRI by the World Health Organization (WHO) algorithm and clinical examination, and with pneumonia by radiographic examination. Diagnoses were compared using kappa analysis. SETTING: Pediatric emergency department. PATIENTS: Peruvian pediatric patients with acute respiratory infection (n = 269) and well children (n = 162). MAIN OUTCOME MEASURES: Hypoxemia (arterial oxygen saturation < 96.6% of the mean arterial oxygen saturation of well children -2 SD). RESULTS: Children with pneumonic and nonpneumonic ALRI (59%, 160/269) had a mean (+/- SD) arterial oxygen saturation significantly lower than well children (93.8% +/- 3.5% vs 98.7% +/- 1.51%; P < .01). Pulse oximetry detected 88% and the WHO algorithm 90% of cases of pneumonic ALRI. The WHO algorithm and pulse oximetry detected 72% of radiologic pneumonia. Pulse oximetry misclassified notably fewer well children than did the WHO algorithm (4% vs 35%). Pulse oximetry and the WHO algorithm together (SATWHO) detected 99% and 87% of pneumonic ALRI and radiologic pneumonias, respectively, and both methods detected 94% of all cases of pneumonic and nonpneumonic ALRI diagnosed clinically. CONCLUSIONS: Pulse oximetry and the WHO algorithm are practical, helpful, and appropriate for use in developing countries to identify children with pneumonic and non-pneumonic ALRI who require treatment. The SATWHO is highly sensitive for detecting children with ALRI.

Acute Disease

Mutations in the M4 domain of Torpedo californica acetylcholine receptor dramatically alter ion channel function.

Site-directed mutagenesis was used to mutate alpha Cys418 and beta Cys447 in the M4 domain of Torpedo californica acetylcholine receptor expressed in Xenopus laevis oocytes. The M4 region is a transmembrane domain thought to be located at the lipid-protein interface. By whole-cell voltage clamp analysis, mutation of both alpha subunits to alpha Trp418 increased maximal channel activity approximately threefold, increased the desensitization rate compared with wild-type receptor, and shifted the EC50 for acetylcholine from 32 microM to 13 microM. Patch measurements of single-channel currents revealed that the alpha Trp418 increased channel open times approximately 28-fold at 13 degrees C with no effect on channel conductance. All of our measured functional changes in the alpha Trp418 mutant are consistent with a simple kinetic model of the acetylcholine receptor in which only the channel closing rate is altered by the mutation. Our results show that changes in protein structure at the putative lipid-protein interface can dramatically affect receptor function.

Acetylcholine

[Desensitization of the nicotinic acetylcholine receptor].

In biological membranes, ionic channels act speeding up ion movements. Each ionic channel is excited by a specific stimulus (i.e. electric, mechanical, chemical, etc.). Chemically activated ionic channels (CAIC), such as the nicotinic acetylcholine receptor (nAChR), suffer desensitization when the receptor site is still occupied by the agonist molecule. The desensitized CAIC is a non functional channel state regarded as a particular case of receptors rundown. CAIC desensitization only involve reduced activity and not their membrane elimination. Desensitization is important to control synaptic transmission and the development of the nervous system. In this review we discuss results related to its production, modulation and some aspects associated to models that consider it. Finally, an approach combining molecular biology and electrophysiology techniques to understand desensitization and its importance in biological systems is presented.

Animals

[Modulation of transmitter release and its interaction with the receptor in the neuromuscular junction].

New techniques to control the potential in membrane patches are giving in detail important characteristics of the pre- and post-synaptic channels. When used to assess the quantal size regulation during synchronous (evoked) or asynchronous (spontaneous) release of neurotransmitter can provide valuable information above this process. The macropatch technique (a version of the original patch clamp technique), has advantages in comparison with other macroscopic voltage clamp techniques to record the miniature end-plate current, mepc. During this focal recording, the puzzle size variation of mepc's amplitudes produced, from events generated over distant parts of the cell, are removed. The quantal response is an important feature during synaptic plasticity. Therefore, in this review we focus on pre- and post-synaptic aspects from the quantal asynchronous release of neurotransmitter, that occurs in the neuromuscular junction. We take emphasis on the caudal muscle of tadpoles from amphibian.

Acetylcholine

The effect of ATP on Ca(2+)-dependent K+ channels of human red cells.

The action of ATP on Ca(2+)-dependent K+ channels was studied in fresh human erythrocytes using patch-clamp techniques. Single-channel current was recorded at pH 6.5 from inside-out patches in the presence of symmetrical K+ gluconate solutions, containing both 1 microM free Ca2+ in the bath and 0.5 mM LaCl3 on the pipette side. With no ATP, the electrical activity revealed low-conductance K+ channels (25 pS), which showed inward rectification and an opening kinetics dependent on membrane potential. When ATP (1 mM) and Mg2+ (2 mM) were added together and a depolarizing potential was simultaneously applied, only a high-conductance channel (about 75 pS) was observed. This channel showed no rectifying properties and it was not found if ATP was added in the absence of Mg2+. Channel activity was enhanced by adding fluoride (10 mM) or trifluoperazine (50 microM) whilst it was reduced after incubating with dibutyryl cAMP (50 microM) or alkaline phosphatase (250 U/ml). On the other hand, when fragmented membranes from inside-out vesicles were incubated with gamma-32 P-ATP and 1 microM free Ca2+ under above conditions, only two high-molecular weight polypeptides (235 and 320 kDa) were labelled with 32P. The results suggest that ATP-mediated phosphorylation of Ca(2+)-dependent K+ channels leads to a high-conductance state.

Adenosine Triphosphate

Identification of Dirofilaria immitis-infected dogs with a coagglutination assay.

The presence of Dirofilaria immitis excretory-secretory (ES) products was detected in the urine of infected dogs using a coagglutination assay. Urine samples from 30 naturally infected dogs were positive. Seventeen of them were microfilaremic, whereas 13 had become amicrofilaremic after receiving 2 courses of diethylcarbamazine. Urine samples from 20 dogs infected with other parasites, Dipetalonema reconditum (7), Toxocara canis (5), and Ancylostoma caninum (8), and urine samples from 20 healthy dogs were negative. The assay detected 200 ng/ml or more of ES products. This assay is simple, easy to perform with minimum training, and requires no equipment. Therefore it should be useful to detect canine filariasis under field conditions.

Agglutination Tests

Acetylcholine receptor channel gating and conductance involve extracellular disulfide bond(s).

Disulfide bonds are critical determinants of the function of the acetylcholine receptor at the vertebrate neuromuscular junction. In the present study, the role of these bonds in acetylcholine receptor channel gating and conductance was investigated at the single channel level. Disulfide bond reducing agents decreased the single channel conductance of both ligand-gated and spontaneously opening acetylcholine receptor channels, indicating that the observed decrease in conductance is not due to blockade of the channel lumen by agonist molecules. In addition, the reducing agents increased the opening frequency of both liganded and unliganded acetylcholine receptor channels. Use of inside-out patches and both membrane permeant and impermeant reducing agents demonstrated that the disulfide bonds involved are all extracellular. These findings indicate that both channel gating and conductance involve conformational changes in extracellular regions of the acetylcholine receptor.

Animals

Spontaneous openings of large and small conductance acetylcholine receptor channels in Xenopus myocytes.

Spontaneous openings of acetylcholine receptor channels were investigated using Xenopus myotomal muscle cells in culture and patch clamp recording methods. Two classes of channels with conductances close to 40 and 60 pS and reversal potentials near 0 mV were found to open in the absence of agonist. The open time of the low-conductance channel was about 3 times longer than that of the high-conductance channel. Open times were shorter by a factor of 3-5 than those of acetylcholine-activated channels in Xenopus myocytes and showed no significant voltage dependence. These studies indicate that the two predominant classes of acetylcholine receptor channels in this preparation can open spontaneously.

Acetylcholine

The nicotinic acetylcholine receptor channel in embryonic muscle of Xenopus laevis. A program to separate channel types.

The single channel activity of nicotinic acetylcholine receptor (AChR) channels from Xenopus laevis embryonic myotomes in culture, was studied with the patch clamp technique. Two types of single channel activity were observed at low agonist concentration (100 nM ACh-Cl), which were distinguished by their conductance (60 and 40 pS, approximately). Both channel types were recorded simultaneously and therefore to carry out the kinetic analysis, we separate them by using a program exploiting the difference in amplitude of the channels. By using the program CLASS the stationary kinetic characteristics of both types of channels can be obtained separately and evaluated.

Animals

Detection of specific anti-giardia serum antibody by an immunofluorescence test in children with clinical giardiasis.

In 50 of 100 children with clinical giardiasis studied, the presence of Giardia lamblia was proven by stool and/or duodenal aspirate examination; the presence of the parasite was not demonstrated in the rest. Serum antibodies to G. lamblia were investigated in all children by an indirect immunofluorescent test (IIF) with G. lamblia trophozoites as antigen. It was found that all the children with positive duodenal aspirate had positive serology (titers greater than or equal to 1/32). The best correlation between parasitological and serological procedures were in the 1-5-year-old age group, and there was an age dependent increase of the antibody titer. Most of the parasitologically negative children were serologically negative. Our results support the use of IIF as a useful diagnostic procedure in the diagnosis of giardiasis in children.

Adolescent

Acetylcholine modulated potassium channel in the hair cell of the toadfish saccule.

Sensory transduction in the acoustic-lateralis system is modulated by an efferent synapse on the sensory hair cells and afferent fibers. Acetylcholine has been implicated as a neuro-transmitter at this synapse. This work addresses the ionic mechanism of action of acetylcholine on the hair cell of the toadfish saccule using path clamp methods and single channel recording. Acetylcholine and oxotremorine, a muscarinic agonist, were found to increase the open time and opening rate of a high conductance K+ channel in the basolateral walls of the hair cell. This effect is not dependent on the presence of Ca2+ in the extracellular media. The involvement of an intracellular mediator is implicated since bath applied agonist opens K+ channels isolated under the recording pipette.

Acetylcholine

Influence of the patch pipette glass on single acetylcholine channels recorded from Xenopus myocytes.

The type of glass used to fabricate patch pipettes influences the kinetic properties of single-channel currents activated by acetylcholine in Xenopus myocytes. In patches formed with hard glass pipettes, the opening rate decreased in a time-dependent manner. Such decrease was most pronounced for the low-conductance channel. In addition, longer-duration events of this form of channel dropped out faster than shorter-duration events and, as a consequence, the apparent channel open time became shorter during the recording period. These effects were not observed in patches formed with soft glass pipettes.

Animals