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Biomedical subjects

A Levi

Publications and source records attributed to A Levi.

At least 73 records · Page 4Linked to original sources
PubMed1987

Dermatophytosis of the diaper area.

Six cases of dermatophytosis of the diaper area due to either Epidermophyton floccosum or Trichophyton rubrum are described herein. The clinical and laboratory features of these patients and those reported in the literature are highlighted. Dermatophytosis should be considered in the differential diagnosis of rashes in the diaper area. Most standard remedies for diaper rash will not be effective or may exacerbate diaper dermatophytosis. Recognition of this condition by the clinician will lead to earlier rational treatment and may avoid the delay caused by therapy.

Clotrimazole↗
PubMed1985

Molecular cloning of a gene sequence regulated by nerve growth factor.

Nerve growth factor (NGF) is essential for the development and differentiation of sympathetic or sensory neurons. A complementary DNA was cloned that corresponds to a gene sequence induced more than 50-fold in a cultured target cell line of pheochromocytoma cells (PC12 cells) 5 hours after the addition of NGF. The induced messenger RNA encodes a 90,000-dalton polypeptide that may represent one of the primary events in NGF-induced differentiation of neurons.

Actins↗
PubMed1983

Regulation of cell proliferation by epidermal growth factor.

Epidermal Growth Factor (EGF) is a 6045 dalton polypeptide which stimulates the proliferation of various cell types in vitro and in vivo. EGF binds to diffusely distributed membrane receptors which rapidly cluster primarily on coated pits areas on the plasma membrane. Subsequently, the EGF-receptor complexes are endocytosed and degraded by lysosomal enzymes. The lateral diffusion coefficient (D) of EGF-receptor complexes on cultured cells increases gradually from D = 2.8 X 10(-10) cm2/sec at 5 degrees C to 8.5 X 10(-10) cm2/sec at 37 degrees C. In the same range of temperature the rotational correlation times change from 25 to 50 microseconds to approximately 350 microseconds. Hence, at 4 degrees C, the occupied EGF receptors translate and rotate rapidly in the plane of the membrane. At 37 degrees C, EGF receptors form microclusters composed of 10 to 50 molecules. Moreover, it is concluded that both at 4 degrees C and 37 degrees C lateral diffusion of the occupied receptors is not the rate determining step for either receptor clustering or internalization. EGF receptor is a 150,000 to 170,000 dalton glycoprotein. The receptor is in close proximity to an EGF-sensitive, cAMP-independent, tyrosine-specific protein kinase which also phosphorylates the receptor molecules itself. The EGF sensitive kinase is similar to the kinase activity which is associated with certain RNA tumor viruses. The fact that the non-mitogenic cyanogen-bromide cleaved EGF is as potent as native EGF in stimulating phosphorylation suggests that EGF-induced, protein phosphorylation is a necessary but insufficient signal for the induction of DNA synthesis by EGF. EGF receptor serves also as the binding site for Transforming Growth Factors (TGF) which compete with EGF and induce anchorage-independent growth of normal cells in soft agar. Tumor promoters such as phorbol ester effect the binding of EGF to its membrane receptors and its ability to stimulate DNA synthesis. EGF itself has also some tumor promoting activity. Hence, the membrane receptor for EGF seems to participate in the regulation of normal and neoplastic growth. Monoclonal antibodies against EGF receptor (IgM) induce various early and delayed effects of EGF, while their monovalent Fab' fragments are devoid of biological activity. These observations support the notions that EGF receptor rather than EGF itself is the active moiety and that the role of the hormone is to perturb the receptor in the appropriate way, probably by inducing the microaggregation of EGF receptors.

Allosteric Regulation↗
PubMed1982

Identification of normal and transposed great arteries by contrast M-echocardiography in the newborn: a combined suprasternal and precordial approach.

Diagnosis of complete transposition of the great arteries (TGA) by M-mode echocardiography depends on the correct identification of the aorta and the pulmonary artery at their roots. We describe a contrast M-mode echocardiographic technique which combines suprasternal and precordial views in which the two great arteries are visualized simultaneously. After venous injection of 1-3 ml 5% dextrose, the sequence and relative intensity of opacification of the great arteries are recorded in both views and then matched to each other. Because in the suprasternal view the aorta is always superior and the pulmonary artery inferior, the characteristics of opacification of these two arteries in the suprasternal view are used as markers for their proper identification in the precordial view. In four normal newborns contrast medium filled only the pulmonary artery. In six newborns with cardiovascular malformations with shunts and normally related great arteries, in which the contrast medium preferentially filled either the aorta (five patients) or the pulmonary artery (one patient), matching the record from the precordial view to that from the suprasteral view proved that the anterior vessel was indeed the pulmonary artery, and the posterior vessel the aorta. In five newborns with d-TGA the contrast medium preferentially filled the aorta, and the combined suprasternal and precordial approach proved that the aorta was anterior and the pulmonary artery posterior. This method is independent of the direction of venous drainage or site of injection.

Aorta↗
PubMed1981

Mid-systolic click and echocardiographic evidence of mitral valve prolapse during electrical pacing.

A mid-systolic click was present in a patient during three years of follow-up after implantation of a permanent transvenous pacemaker. Echocardiography revealed posterior motion of the anterior leaflet which resembled mitral valve prolapse. Both the click and echocardiographic evidence of prolapse disappeared simultaneously with resumption of sinus rhythm and during supraventricular tachyarrhythmias. Wtih spontaneous change in the position of the electrode three years after initial implantation, both the click and the posterior motion of the mitral valve disappeared. The association of mitral valve prolapse with electrical pacing is most unusual and appears to have a distinct pathophysiological mechanism.

Aged↗
PubMed1980

Mobility, clustering, and transport of nerve growth factor in embryonal sensory cells and in a sympathetic neuronal cell line.

We have prepared a fluorescent conjugate of nerve growth factor (NGF) containing 8--10 rhodamine molecules attached to free carboxyl groups of the protein. This analogue retained full binding capacity toward NGF receptors, full antigenic properties, and the potency to stimulate the differentiation of embryonal chicken sensory ganglia cells in vitro. We have used this analogue to study the mobility and distribution of NGF receptors on embryonal chicken sensory cells from dorsal root ganglia and on a pheochromocytoma cell line (PC-12) that responds to NGF by differentiating along a neuronal pathway. The rhodamine conjugate of nerve growth factor (R-NGF) binds initially to diffusely distributed mobile receptors (D approximately 8 X 10(-10) cm2/sec) on immature sensory and PC-12 cells. At 37 degrees C, the NGF receptor complexes cluster and form immobile visible patches. These patches undergo endocytosis in a process that consumes metabolic energy. Methylamine blocks the formation of visible patches of NGF and the receptors remain dispersed and mobile at 37 degrees C. On differentiated chicken sensory cells, R-NGF binds to diffusely distributed mobile receptors and to aggregated immobile binding sites. These clusters are localized at the tip of the axon, along the axon, and in the main body. The NGF molecules that are internalized at the tip of the axon are transported retrogradely from the peripherey to the cell body.

Animals↗
PubMed1980

Cell density modulates receptor-mediated internalization of nerve growth factor in pheochromocytoma cells.

Binding and fate of the nerve growth factor (NGF) in pheochromocytoma cells (clone PC12) have been measured with the use of iodine-labeled ligand and with 125I-NGF antibodies. With such double approach it is possible to distinguish between surface bound and total NGF bound to PC12 cells. It is found that NGF-receptor complexes undergo down-regulation. This process is noticeable at low but not at high cell densities, and only in PC12 cells never exposed to NGF. Previous incubation with growth factor leads to the disappearance of down-regulation of NGF-receptor complexes. Assuming that this process is an indirect measure of NGF-receptor internalization, it is concluded that it is modulated by the cell density or by previous exposure to the factor. These findings are postulated to be relevant to the mechanism of action of NGF and to its multiple effects on target cells.

Adrenal Gland Neoplasms↗
PubMed1979

Reactive gaze laterality in schizophrenic patients.

Reflective lateral eye movements (LEMs) in response to questions of different categories are indicative of differential hemispheric reactivity. These LEMs were studied in schizophrenic patients and normal subjects, in response to 24 questions (12 visual-emotional and 12 verbal-neutral). Two categories of saccades were observed: short-latency LEMs (S-LEMs) and long-latency LEMs (L-LEMs). S-LEMs are believed to be associated with orienting response mechanism. L-LEMs are considered to be related to decision-making or formulating hemispheric-activity-dependent response strategy. In the present study, a general trend of leftward LEMs was found among normals regardless of the question's category, whereas schizophrenics tended to show predominantly rightward LEMs. This suggests that individual cognitive style, rather than task variables, affects LEM direction. The two types of LEM's and their different involvement in hemispheric activity are discussed.

Adult↗
PubMed1979

Algae/Bacteria ratio in high-rate ponds used for waste treatment.

Algae, bacteria, and zooplankton were counted in samples drawn from 120- and 150-m high-rate algae ponds (those used for wastewater treatment). The fraction of nondegraded organic matter was estimated by comparing the ratio of biological and chemical oxygen demands and the bacterial, algal, and zooplankton counts to volatile suspended solids. With pond effluent quality at an acceptable level (around 18 mg of dissolved biological oxygen demand), the algae/bacteria ratio was around 1:100 or even higher, the zooplankton count was negligible, and the bacterial concentration was approximately 10 cells per liter by direct count. The data for bacteria exceeded those of earlier studies by one to three orders of magnitude.

Journal Article↗
PubMed1978

Nerve growth factor potentiates actomyosin adenosinetriphosphatase.

The nerve growth factor protein (NGF) favors polymerization of brain actin and induces its organization to form paracrystalline structures that activate myosin ATPase (ATP phosphohydrolase, EC 3.6.1.3) to an extent greater than actin alone. Binding studies show that the initial 1:1 stoichiometry of NGF-G-actin complexes decreases to 1:7-10 when polymerization is ended and paracrystalline structures are formed. The ratio becomes even lower when heavy meromyosin is added in the absence of ATP, suggesting that heavy meromyosin displaces NGF bound to actin microfilaments. This conclusion is supported by the finding that when heavy meromyosin is added to NGF-microfilament complexes, under conditions for "decorating" microfilaments, the usual paracrystalline structure of the complexes disappears. The NGF-mediated organization of actin and activation of myosin ATPase is visualized as a self-regulatory and self-propagating mechanism, because progressive displacement of the growth factor induced by heavy meromyosin binding to F actin as ATP consumption proceeds renders an increasingly higher amount of NGF free for new interactions. These findings are discussed in the light of the mechanism of action of NGF in the target cells.

Actins↗
PubMed1976

Ca2+, K+-regulated intramolecular crosslinking of S-100 protein via disulfide bond formation.

Reaction of the thiol reagent 5,5'-dithio-bis(2-nitrobenzoic acid) (Nbs2) with the brain-specific protein S-100 favours stabilization of the quaternary structure of the protein via disulfide bond formation. This process is modulated by those cations (Ca2+ and K+) which are known to affect the conformation of the protein. Ca2+ markedly favours the reaction of S-100 with Nbs2 but inhibits subsequent disulfide bond formation; K+, on the contrary, is much less effective in promoting interaction with Nbs2 but strongly stimulates disulfide bond formation. These findings are interpreted assuming that in presence of Ca2+ the three subunits forming the native S-100 protein have two cysteine residues exposed to the solvent but mismatched to form disulfides while in presence of K+ the sulphydryl groups are in a less accessible position to Nbs2 but suitable for S-S bond formation. Crosslinking of S-100 subunits is characterized by the appearance in dodecylsulphate electrophoresis of two very close protein bands having a molecular weight almost identical to that of the native, undenatured protein but not of higher or lower-molecular weight components. This finding, and the demonstration that both the crosslinked and native S-100 proteins have identical profiles when analyzed by sucrose density centrifugation or gel chromatography indicate that disulfide bond formation occurs among subunits of the same molecule.

Animals↗
PubMed1975

Interaction of nerve growth factor with tubulin. Studies on binding and induced polymerization.

The interaction of the nerve growth factor with the neurotubule protein has been studied with the aim of elucidating the nature of the large complexes that they form when incubated together and the factors and control this event. The results show that the binding of nerve growth factor to tubulin is followed by the formation of large structures that, in certain experimental conditions, accelerate the rate of tubulin polymerization to form microtubules or catalyze their assembly in conditions where this process does not occur spontaneously. The formation of large nerve growth factor-tubulin complexes starts to occur only at a molar ratio of 1.0-1.5 NaCL or GTP strongly inhibit this proceed without a detectable effect on NGF binding. Two hypotheses are postulated explain these findings. Firstly, that tubulin has two sites with different affinity for nerve growth factor and the polymerization occurs only when the second NGF molecule has interacted with the microtubule protein. Alternatively, free tubulin in solution is the polymerization by hindering site of tubulin-factor complexes present in solution at a 1.1 molar ratio. In both cases, GTP, Na-+ or H-+ will affect the formation of large unsoluble, tubulin-NGF complexes, by changing their conformation or by decreasing electrostatic interactions.

Animals↗