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Biomedical subjects

A Schechter

Publications and source records attributed to A Schechter.

At least 19 recordsLinked to original sources
PubMed2000

Prototype systems for rechargeable magnesium batteries.

The thermodynamic properties of magnesium make it a natural choice for use as an anode material in rechargeable batteries, because it may provide a considerably higher energy density than the commonly used lead-acid and nickel-cadmium systems. Moreover, in contrast to lead and cadmium, magnesium is inexpensive, environmentally friendly and safe to handle. But the development of Mg batteries has been hindered by two problems. First, owing to the chemical activity of Mg, only solutions that neither donate nor accept protons are suitable as electrolytes; but most of these solutions allow the growth of passivating surface films, which inhibit any electrochemical reaction. Second, the choice of cathode materials has been limited by the difficulty of intercalating Mg ions in many hosts. Following previous studies of the electrochemistry of Mg electrodes in various non-aqueous solutions, and of a variety of intercalation electrodes, we have now developed rechargeable Mg battery systems that show promise for applications. The systems comprise electrolyte solutions based on Mg organohaloaluminate salts, and Mg(x)Mo3S4 cathodes, into which Mg ions can be intercalated reversibly, and with relatively fast kinetics. We expect that further improvements in the energy density will make these batteries a viable alternative to existing systems.

Journal Article↗
PubMed1998

There is binding of collagen IV to beta 1 integrin during early skin basement membrane assembly.

This study is concerned with the mechanism of basement membrane assembly in an in vitro 3-dimensional skin-culture system. Dermal fibroblasts alone can synthesize collagen IV, perlecan, and nidogen, but cannot assemble them into a basement membrane. When keratinocytes are added to the culture, however, linear assembly of collagen IV, perlecan, and nidogen is noted at the epidermo-dermal interface. Northern blots and in situ hybridization showed that perlecan and nidogen mRNAs derive exclusively from fibroblasts, while the alpha 2 (IV) collagen chain is expressed by both keratinocytes and fibroblasts, although the major source is in the mesenchyma (80%). Prior to the development of the lamina densa, collagen IV colocalizes with beta 1 integrins, most likely alpha 1 beta 1 and alpha 2 beta 1, which are known receptors for this collagen. Blocking experiments with the AIIB2 mAb (anti-beta 1 integrin subunit) and by peptide inhibition with the CB3(IV) collagen fragment disrupted the assembly of collagen IV. This study suggests that the initiation of basement-membrane formation involves binding of collagen IV molecules to keratinocyte cell-matrix integrins. These complexes act as nucleation sites for further polymerization of collagen IV molecules mostly derived from fibroblasts, by a process of self-assembly.

Basement Membrane↗
PubMed1995

Skin fibroblasts are the only source of nidogen during early basal lamina formation in vitro.

The purpose of this study was to determine whether nidogen, the linkage protein of the basal lamina, is of epidermal or dermal origin. The development of the basal lamina was studied in an in vitro skin model. Preputial fibroblasts seeded onto a nylon mesh attached, proliferated, and developed a rich extracellular matrix (dermal model). Preputial keratinocytes were added to the dermal model to form a keratinocyte dermal model that ultrastructurally resembled in many respects human skin. Ultrastructural analysis revealed early stages of dermal development, including an incomplete basal lamina, aggregates of dermal filamentous material connecting to the lamina densa, bundles of 10-nm microfibrils, formation of premature hemidesmosomes, anchoring filaments, and anchoring fibrils. The cell origin of nidogen was determined in the dermal model and in the epidermal and dermal components of the keratinocyte dermal model. Specific antibodies and a cDNA probe for nidogen were used for immunofluorescence microscopy, Western and Northern blots, and for in situ hybridization studies. Our data show that fibroblasts are the only source of nidogen during early basal lamina formation. Although fibroblasts can synthesize nidogen and deposit it in the dermal matrix, no basal lamina will form unless they are recombined with keratinocytes. This suggests that the epidermis plays a major regulatory role in the production and assembly of nidogen into the basal lamina.

Basement Membrane↗
PubMed1992

Severe periodic febrile myalgia in infancy due to carnitine palmitoyltransferase deficiency.

A 7 1/2-yr-old girl suffered, since early infancy, severe recurrent myalgia during periodic attacks of fever, vomiting and pharyngitis. Neither myoglobinuria nor exercise-induced muscle pain was present. She was found to have carnitine palmitoyltransferase deficiency (CPTD) in leukocytes, fibroblasts and muscle. This case exemplifies the importance of looking for an associated metabolic etiology of recurrent febrile myalgia even in the absence of myoglobinuria.

Carnitine O-Palmitoyltransferase↗
PubMed1991

In vivo non-invasive studies on the human lens.

Progress in biophysical technology now permits us to monitor aging and precataractous changes in the human ocular lens in vivo as well as in vitro. We are employing two noninvasive techniques to measure changes in lens fluorescence and in one lens water compartment (T2) utilizing Scheimpflug lens fluorescence densitography and magnetic resonance imaging. These studies demonstrate age-related changes in the normal lens as reflected by enhanced fluorescence and longer T2 values. Precataractous changes can also be detected with this approach.

Adult↗
PubMed1991

Phototoxicity involving the ocular lens: in vivo and in vitro studies.

Our laboratory has demonstrated the cataractogenic potential of UV radiation and several photosensitizing drugs in laboratory animals and in humans. We have utilized lens fluorescence measurements (which we have demonstrated to be a reliable marker for pre-cataractous and early cataractous changes), NMR pulse relaxation techniques, and our recently developed magnetic resonance imaging method to measure lens T2 values in the normal and UV exposed Degus lens (in vivo and in vitro) to detect pre-cataractous changes in the lens. These approaches will permit us to employ two parameters (increased non-tryptophan fluorescence and a decrease in T2 values) to monitor for such changes months before the lens opacities become manifest by conventional slit lamp examinations.

Animals↗
PubMed1988

Lanthony desaturated panel D15 test in sickle cell patients.

The Lanthony D15 desaturated test was used to compare color vision in sickle cell patients with 20/20 visual acuity and peripheral lesions of sickle cell retinopathy with normal controls. Sickle cell patients had significantly higher Lanthony error scores and significantly more blue-yellow and mixed color vision defects than controls. Among patients with sickle cell anemia (SS), Lanthony and Farnsworth Munsell 100 Hue test scores were significantly correlated, and both tests showed good agreement in identifying the presence or absence of a color defect. These results suggest that the Lanthony D15 test may be a useful clinical tool to identify blue-yellow color defects, especially because of its brevity and simplicity of administration.

Adult↗
PubMed1987

Color vision defects in sickle cell anemia.

The Farnsworth-Munsell 100-hue test was used to compare color vision in patients with sickle cell anemia, 20/20 visual acuity, and mild to severe peripheral retinopathy, but without posterior retinal vessel involvement, with matched normal controls. Patients with sickle cell anemia had significantly more blue-yellow and mixed color vision defects and significantly higher Farnsworth-Munsell 100-hue scores than did controls. There were no significant associations between color vision defects and the severity of peripheral retinal findings or the diameter of the foveal avascular zone. These results suggest that color vision defects may exist in patients with sickle cell anemia in the absence of ophthalmoscopic retinal changes in the posterior fundus.

Adult↗
PubMed1987

Fetal gastric pseudomasses.

Discrete echogenic areas of 4-12 mm were observed in the fetal stomach on seven prenatal sonograms. The finding was incidental and solitary during the second trimester in six normal pregnancies. It was noted during the third trimester in a case of meconium peritonitis. These echogenic areas displayed a homogeneous texture. They disappeared on repeat prenatal examination in six patients who did not reveal any gastrointestinal symptoms on postnatal follow-up. Although their origin is not certain, these fetal gastric pseudomasses should be interpreted cautiously.

Diagnostic Errors↗
PubMed1986

Increased echogenicity in the lower fetal abdomen: a common normal variant in the second trimester.

Ten cases displaying a focal area of increased echogenicity in the lower fetal abdomen on prenatal sonography are reported. This was an isolated finding in each case. Nine cases were noted early in the second trimester. The last case corresponded to a postmature gestation. In all cases, a normal lower abdomen was documented on follow-up prenatal sonography, at birth, or at autopsy. The authors believe that increased echogenicity in the lower fetal abdomen represents a normal variant that is more common than suggested by the literature. A possible explanation of this pattern is offered.

Abdomen↗
PubMed1985

Synergistic effects of cyclic AMP and nerve growth factor on neurite outgrowth and microtubule stability of PC12 cells.

The outgrowth of neurites from rat PC12 cells stimulated by combined treatment of nerve growth factor (NGF) with cAMP is significantly more rapid and extensive than the outgrowth induced by either factor alone. We have compared the responses of PC12 cells under three different growth conditions, NGF alone, cAMP alone, and combined treatment, with respect to surface morphology, rapidity of neurite outgrowth, and stability of neurite microtubules, to understand the synergistic action of NGF and cAMP on PC12. Surface events at early times in these growth conditions varied, suggesting divergent pathways of action of NGF and cAMP. This suggestion is strongly supported by the finding that cells exposed to saturating levels of dibutyryl cAMP without substantial neurite outgrowth initiated neurites within 5 min of NGF. This response has been adopted as a convenient assay for NGF. Neurites that regenerated in the three growth conditions showed marked differences in stability to treatments that depolymerize microtubules. The results indicate that microtubules in cells treated with both NGF and cAMP are significantly more stable than in either growth factor alone. We suggest that a shift of the assembly equilibrium favoring tubulin assembly is a necessary prerequisite for the initiation of neurites by PC12.

Animals↗
PubMed1984

Correlative relationship between adherence of Candida albicans to human vaginal epithelial cells in vitro and candidal vaginitis.

This study investigated whether a correlation exists between predisposition to candidal vaginitis and adherence of Candida albicans to vaginal epithelial cells in vitro. Vaginal epithelial cells from 120 fecund women who were pregnant and/or diabetic had a greater propensity to bind C. albicans than did 71 oral contraceptive users and 75 non-pregnant, non-diabetic controls. The highest level of adherence occurred in pregnant diabetic women. Among 48 non-diabetic postmenopausal females, C. albicans adherence was lower than for fecund controls, but it was higher for cells from 33 postmenopausal diabetic women. The hormonal status of the fecund and postmenopausal women was assayed cytologically by the Karyopyknotic and Maturation Indices, which determine the ratios of superficial, intermediate and parabasal vaginal epithelial cells. Our findings point to increased C. albicans adherence in situations where there is an increase in the number of intermediate epithelial cells: pregnancy, the first or fourth weeks of the menstrual cycle, or diabetes. The adherence of 41 C. albicans isolates from patients with vaginitis was significantly higher than that of 36 isolates from asymptomatic carriers.

Adhesiveness↗