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Biomedical subjects

Y Shimoni

Publications and source records attributed to Y Shimoni.

79 records · Page 5Linked to original sources
PubMed1977

Is hyperosmotic neurosecretion from motor nerve endings a calcium-dependent process?

Spontaneous liberation of neurotransmitter quanta is strongly affected by the osmotic pressure of the extracellular fluid. Elevation of the osmolarity by 20-30% increases the rate of release from motor nerve endings by more than one order of magnitude. In this respect the neuromuscular junction resembles some other secretory systems. The mechanism of this hyperosmotic neurosecretion is not yet understood; extracellular calcium ions are not directly responsible, since this effect can be produced in their absence. Recently, it has been suggested that the liberation of neurotransmitter is regulated by the intracellular concentration of free calcium ions. We have therefore examined the hypothesis that hyperosmotic neurosecretion originates from an increase in internal calcium concentration ([Ca]in). At the frog neuromuscular synapse however, it is impossible at present to estimate directly free [Ca]in; hence we used an indirect technique, which is based on two assumptions; first, the frequency of the miniature endplate potentials (m.e.p.p.s.) reflects free [Ca]in. Second, the movement of calcium ions across the presynaptic membrane is governed by the electrochemical gradient, and by the calcium conductance (g(Ca)). If hyperosmotic neurosecretion is caused by an increase in [Ca]in, then increasing g(Ca), under reversed electrochemical gradient for the calcium should cause a reduction in the effect of hyperosmotic stress on transmitter release. We report that hyperosmotic neurosecretion is dependent on [Ca]in.

Animals↗
PubMedDate not supplied

T-2 toxin effect on isolated perfused rat hearts.

T-2 toxin is the major lethal component of several Fusarium fungi implicated in the disease of man and animals. We used isolated rats hearts to test the T-2 toxin cardiotoxicity. Electrodynamics and ultrastructural parameters were studied. The main changes consisted of decreased contractility and electrocardiographic abnormalities without much effect on heart rate or QRS and QT intervals. Ultrastructurally, swelling of myofibers and their mitochondria occurred and damage to the plasma membrane was seen. It is possible that the T-2 effect is mediated through soluble thiol to cause cytoplasmic calcium decrease and loss of plasma membrane integrity.

Animals↗
PubMedDate not supplied

Endogenous ouabain-like compound increases heart muscle contractility.

Cardiac glycosides such as digoxin or ouabain have long been known to influence the strength of contraction of cardiac muscle. Although the mechanism of action of these compounds remains unknown, all the proposed modes of action are based on initial binding to specific membrane receptors which are part of the (Na+ + K+)ATPase complex. These receptors, well characterized and defined, suggest the existence of an endogenous substance capable of binding to them, in analogy with endogenous opiates, discovered long after morphine and its receptors. As glycosides affect (Na+ + K+)ATPase activity, an endogenous substance may be a regulator of this important enzyme. Indeed, the search for endogenous regulators of the (Na+ + K+)ATPase or ouabain-like compounds (OLC) has recently intensified. These compounds, extracted and partially purified from mammalian brain, heart, blood and urine, and from toad skin and plasma, have been shown to inhibit 3H-ouabain binding and (Na+ + K+)ATPase activity. We report here that in addition to these effects, the OLC, highly purified from toad skin and sheep brain, increases the force of contraction of frog and guinea pig atrium.

Animals↗
PubMedDate not supplied

Data predictability for compression of digital fluorography images.

Images obtained by digital fluorography were checked for compressability. These images include images of coronary vessels and images of peripheral vessels. These images have a very low signal-to-noise ratio compared to the optical images usually used for developing compression methods. Configurational entropy was used to represent the information content of these images. Reversible prediction algorithms were extensively checked in a search for minimal residual information, enabling more efficient reversible compression. Optimal results were obtained for algorithms based on two or three neighboring pixels and a semiempirical rule, based on the noise level, was found which decides on the best approach. It was found that raw data images are more predictable than subtracted images although the latter are visually preferred.

Algorithms↗
PubMedDate not supplied

Nonlinear filters applied on computerized axial tomography: theory and phantom images.

New nonlinear image processing techniques, in particular smoothing based on the understanding of the image, may create computerized tomography (CT) images of good quality using less radiation. Such techniques may be applied before the reconstruction and particularly after it. Current CT scanners use strong linear low-pass filters applied to the CT projections, reducing noise but also deteriorating the resolution of the image. The method in this study was to apply a weak low-pass filter on the projections, to perform the reconstruction, and only then to apply a nonlinear filter on the image. Various kinds of nonlinear filters were investigated based on the fact that the image is approximately piecewise constant. The filters were applied with many values of several parameters and the effects on the spatial resolution and the noise reduction were evaluated. The signal-to-noise ratio of a high-contrast phantom image processed were compared with the nonlinear filter, with the SNR of the phantom images obtained with the built-in CT linear filters in two scanning modes, the normal and the ultra high resolution modes. It was found that the nonlinear filters improve the SNR of the image, compared to the built-in filters, about three times for the normal mode and twice for the UHR scanning mode. The most successful filter on low-contrast phantom image was applied and it also seems to lead to promising results. These results seem to show that applying nonlinear filters on CT images might lead to better image quality than using the current linear filters.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMedDate not supplied

Demonstration of a ouabainlike plasma compound in hypertension prone and hypertension resistant rats.

Material extracted and partially purified from plasma of the Sabra hypertension prone rats was found to be capable of 1) inhibiting the binding of 3H-ouabain to rat brain synaptosomes, 2) inhibiting the activity of rat brain microsomal Na, K activated adenosine triphosphatase, and 3) increasing the contractile force of rat heart muscle. The results demonstrate the presence of a ouabainlike compound in the plasma of these rats. The plasma concentration of this compound in Sabra hypertension prone rats was 698 +/- 199 nmol/ml in ouabain equivalents (SEM; n = 11) versus 2543 +/- 1140 nmol/ml (n = 9) in the Sabra normotensive strain. The presence of ouabainlike compound in the plasma is consistent with the hypothesis that this compound functions as a hormone that regulates Na, K activated adenosine triphosphatase activity and the physiological processes in which this enzyme is involved.

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