Biomedical subjects

C Bonciocat

Publications and source records attributed to C Bonciocat.

21 records · Page 2Linked to original sources

PubMedDate not supplied

The effect of low concentrations of sodium dodecyl-sulfate on 45Ca release in frog skeletal muscle.

The release of radioactive 45Ca was studied in toe muscles of frog previously soaked in Ringer containing 0.1--0.2 mc 45Ca/ml. Sodium dodecyl-sulfate (SDS) added in concentration of 0.05 mM during the washout of the muscle in nonradioactive solution caused a moderate increase in 45Ca efflux that developed gradually to a maximum in about 30 min, then slowly declined. This increase was significantly reduced in muscles with disrupted T tubules. The transient release of 45Ca induced by EDTA (lmM) was markedly increased and prolonged by simultaneous application of the detergent. This effect had a rapid onset, a pronounced increase in 45Ca efflux being observed from the 1st min. The Ca released by the detergent was different from the self-exchangeable Ca fraction. After soaking the muscles in EDTA solution to remove superficial Ca, the addition of SDS was still able to produce a small increase in 45Ca efflux. It is concluded that SDS in low concentrations acts to reduce the binding capacity for Ca of sites located at the level of both superficial portion of the membrane and T tubular membrane. In addition, it also favours the release of Ca from sarcoplasmic reticulum sites. Thus an important effect of SDS appears to be the labilization of specific Ca sites at the level of triadic junction. This effect may account for the facilitation of excitation-contraction coupling observed with SDS in contracture studies.

Animals↗

PubMedDate not supplied

A theoretical and experimental study concerning shape processing by human visual system.

The shape, as a synthetic feature resulting from the particular contour of a figure, may be considered to specify certain spatial relations between the figure domain and surrounding domain. For the study of these relations the figure and the background were considered to belong to a single plane. A characteristic feature of figure-ground relations depending on the figure as a whole was introduced, the "degree of isolation" of the figure from the surrounding ground, with its opposite feature, the "degree of dispersion" into the surrounding ground. A model was elaborated in which the parts radiating from the nucleus of the figure are considered to contribute to the whole figure in inverse proportion to their distance from the nucleus. The corresponding mathematical approach was the convolution between the characteristic function of the figure and a function depending in inverse proportion on the distance from the convolution center (f=1/2 pi r). The maximum value of this convolution integral divided by the radius of the circle having the same area as the figure was introduced as a measure of the degree of isolation of the figure from the surrounding domain. Using symmetrical figures varying in their shape it was found that normal individuals are able to distinguish small differences in this shape parameter and that their evaluations are in good agreement with those predicted by the theoretical model.

Form Perception↗

PubMedDate not supplied

Voluntary multiplet discharge after the activation test for spasmophilia as an electromyographic sign of a mild form of this disease.

The electromyographic (EMG) diagnosis of spasmophilia is based on the appearance in a susceptible muscle of spontaneous burst (multiplet) discharges after an activation procedure consisting usually in 10 minutes ischemia followed by a pause of a length that varies with the author but does not exceed 5 minutes, and finally by a hyperventilation, again not exceeding 5 minutes. In investigations carried out many years ago we observed that a number of subjects with symptoms of spasmophilia showed no postischemic spontaneous bursts, but responded with bursts to voluntary contraction. In this work we present some findings leading to the conclusion that voluntary burst discharge after the activation procedure can represent a sign of spasmophilia and not a mere manifestation within normal limits. Thus, in most cases with no symptoms of spasmophilia, voluntary burst response was absent. On the other hand, most subjects with such an EMG alteration suffered of troubles attributable to spasmophilia. Crisis of tetania with partial or generalized contracture could be encountered in such cases with a frequency close to that of cases with mild spontaneous burst discharge, being, on the contrary, exceptional in cases with normal EMG. In a previous work we showed the existence of a close correlation between the increase above normal of the incidence of ischemic discharge and the intensity of postischemic spontaneous burst (multiplet) discharge. A significant increase of ischemic discharge was also found for the cases showing only voluntary bursts (34.29% of 487 cases as compared to 14.28% of 602 normals). In addition, the period of abnormal burst responses of motor units to voluntary command was significantly prolonged for the cases with more intense ischemic discharge. Finally, there is no gap between spontaneous and voluntary burst discharge, since not rarely a short contraction could trigger a rhythmical selfmaintained burst discharge entirely similar to the spontaneously occurring one. One may conclude that voluntary burst discharges, if rather persistent, can represent a sign of spasmophilic alteration of excitability that must be always tested EMG in suspected cases that give no spontaneous burst discharge to the facilitation procedures. It represents a change in excitability less severe than the spontaneous burst discharge.

Action Potentials↗