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Biomedical subjects

A Peres

Publications and source records attributed to A Peres.

97 records · Page 6Linked to original sources
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↗