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Biomedical subjects

A Peres

Publications and source records attributed to A Peres.

8 recordsLinked to original sources
PubMed1992

P2Y purinoceptors in normal NIH 3T3 and in NIH 3T3 overexpressing c-ras.

The ability of purinergic agonists to induce Ca2+ responses has been tested in two lines of murine fibroblasts: normal NIH 3T3 fibroblasts and NIH 115.14, a clone expressing high levels [1] of the c-ras protooncogene. Both kinds of cells are responsive to ATP in the range 1 microM-1 mM; ADP and ATP gamma S are almost as potent as ATP, while AMP is unable to elicit a response. Ca2+ measurements performed in single cells by image analysis show great variability among cells but in each individual responding cell the Ca2+ rise occurs in an all-or-none fashion. The transient Ca2+ response does not depend on influx from the extracellular medium. Electrophysiological experiments reveal the activation of an outward current (at -50 mV) by ATP, probably due to Ca(2+)-activated K+ channels, confirming the absence of a substantial Ca2+ influx. Finally, stimulation by ATP produces a small but significant increase in the production of inositol phosphates. These results indicate that these cell lines possess purinergic receptors which are not integral membrane channels and which are coupled to InsP3 formation and may be therefore classified as P2Y.

3T3 Cells↗
PubMed1992

[Supraventricular tachycardia due to retrograde decremental conduction over accessory pathways].

PURPOSE: To discuss the clinical and the electrophysiologic findings, the differential diagnosis and the behaviour of concealed retrograde long conduction time accessory pathways. METHODS: Seventeen patients were submitted to electrophysiologic study using programmed electrical stimulation of the heart to assess the electrophysiologic properties of the accessory pathway. RESULTS: In all 17 studied patients, it was possible to advance the next atrial activation by giving a ventricular premature beat during the refractoriness of the His bundle. Of 17 patients, 7 developed signs and symptoms of heart failure (tachycardia-induced cardiomyopathy) due to the presence of incessant tachycardia. Eight patients were cured surgically and 1 underwent DC catheter ablation of the AV node. Six patients were successfully treated with antiarrhythmic drugs, one die of cancer and one still presents incessant tachycardia. CONCLUSION: The electrophysiologic study is essential for the differential diagnosis of the supraventricular tachycardias with a R-P' interval longer than P'-R interval where the incidence of tachycardiomyopathy is high in this group of patients. Surgery provides definitive cure of those patients leading to the regression of the signs and symptoms of heart failure.

Adolescent↗
PubMed1979

Charge movement and membrane capacity in frog muscle.

1. The transient current required to impose a step charge of potential has a complex time course especially in the region of internal potential between -50 and -40 mV. 2. Examination of non-linear transient current in this voltage range suggests two components of charge movement: (a) an initial more-or-less exponential movement, and (b) a slower component with a complex time course. 3. Measurements of membrane capacity support such a division and confirm the steeper voltage dependence of the slower charge movement. 4. Permanent depolarization to 40 mV appears to immobilize the slowly moving charge. Depolarization to -20 mV immobilizes both charge movements, and uncovers the presence of a third charge which seems to correspond to Charge 2 (cf. Adrian & Almers, 1976b; Adrian, Chandler & Rakowski, 1976).

Animals↗
PubMed1979

A voltage-dependent gate in series with the inwardly rectifying potassium channel in frog striated muscle.

1. The degree of tubular potassium depletion and the decrease of potassium conductance due to hyperpolarizing pulses in striated muscular fibres have been examined with the three micro-electrode voltage-clamp technique. 2. The conductance of the fibre membrane has been measured in different extracellular K+ concentrations from 1 to 10 mM. 3. Comparison of the two sets of measurements shows that changes in tubular K+ concentration are not sufficient to account for the conductance decrease associated with hyperpolarization. 4. The presence of a voltage-dependent gate in series with the inwardly rectifying channel for K+ ions, suggested by Almers (1972a, b), is thus confirmed.

Animals↗
PubMed1979

Tomographic reconstruction from limited angular data.

The nth moment of a projection Mn(phi) = rnp(r, phi) dr must be a trigonometric polynomial of degree less than or equal to n. Measuring Mn(phi i) for n + 1 arbitrary angles phi i allows reconstruction of Mn(phi) for all phi. Thus in principle, the exact knowledge of the shadow function within an arbitrarily narrow sector allows reconstruction of the complete shadow. The algorithm doing this is very simple, but its applicability is severely limited by noise in the data.

Mathematics↗
PubMed1976

Exact solution of the unidimensional Poisson-Boltzmann equation for a 1:2 (2:1) electrolyte.

The unidimensional Poisson-Boltzmann equation for a 1:2 (2:1) electrolyte has been solved analytically. The results have been compared with those obtained from the linearized equation. It is shown that in physiological conditions the difference may be greater than 10%. The value of the derivative of the potential in x=0, (dpsi/dx)x=0, has been used by many authors in the evaluation of the superficial charges of biological membranes. The value of (dpsi/dx)x-0 have also been compared with the ones derived from the linearized equation. The difference may be greater than 25%. Our results suggest that the linearization of the Poisson-Boltzmann equation for a 1:2(2:1) electrolyte may be greatly misleading.

Cell Membrane↗