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Biomedical subjects

M Michels

Publications and source records attributed to M Michels.

33 records · Page 2Linked to original sources
PubMed1988

Azathioprine toxicity during long-term immunosuppression of generalized myasthenia gravis.

In this uncontrolled study, 104 patients with generalized myasthenia gravis treated with azathioprine for a median period of 29 months (range, 1 month to 12 years) were surveyed for possible adverse reactions. These occurred in 36 patients (35%) in the following order of frequency: hematologic (18%), gastrointestinal (13%), infectious diseases (13%), and elevation of liver enzymes (6%). No allergic skin reactions were observed. Azathioprine had to be discontinued temporarily in a total of 11 patients (11%) because of possible side effects. The cause of death in the nine patients who died during the period of observation (up to 12 years) was related to myasthenic crisis in two patients. In five patients, a malignant tumor was diagnosed (two carcinoma of the prostate, one ovarian carcinoma, one bronchial carcinoma, and one renal lymphoma) after 2.5 years, 6 months, 3 months, 5 years, and 6 years of treatment, respectively. A causal relationship seems unlikely in the first four cases, but cannot be excluded in the one case of late lymphoma.

Aged↗
PubMed1987

Infrared. An unseen and unnecessary hazard in ophthalmic devices.

The concept of instrument-induced light damage to the retina is well established. Many have argued that ultraviolet (UV) energy is overwhelmingly responsible and that longer wavelength infrared (IR) energy causes thermal change and plays a minimal role. We suggest that infrared may play a primary role in instrument-induced damage. We measured the radiometric and photometric outputs from commonly used ophthalmic devices in normal use and in IR-blocked conditions. We found IR output to represent a significant portion of the total irradiation produced by these instruments. Infrared was easily and inexpensively minimized without compromising usable visible light in these instruments using an efficient IR filter. The instruments' incandescent lamps, glass envelopes, and optics are poor UV emitters or transmitters. Manufacturers' data do not indicate UV emission. Evidence for UV blocking and IR transmission by the intraocular media is presented.

Infrared Rays↗
PubMed1987

Low-affinity potassium uptake system in Bacillus acidocaldarius.

Cells of Bacillus acidocaldarius that were grown with 2.7 mM K+ expressed a low-affinity K+ uptake system. The following observations indicate that its properties closely resemble those of the Escherichia coli Trk and Streptococcus faecalis KtrI systems: (i) the B. acidocaldarius system took up K+ with a Km of 1 mM; (ii) it accepted Rb+ (Km of 6 mM; same Vmax as for K+); (iii) it was still active in the presence of low concentrations of sodium; (iv) the observed accumulation ratio of K+ maintained by metabolizing cells was consistent with K+ being taken up via a K+-H+ symporter; and (v) K+ uptake did not occur in cells in which the ATP level was low. Under the latter conditions, the cells still took up methylammonium ions via a system that was derepressed by growth with low levels of ammonium ions, indicating that in the acidophile ammonium (methylammonium) uptake requires a high transmembrane proton motive force rather than ATP.

Adenosine Triphosphate↗
PubMed1987

High-affinity potassium uptake system in Bacillus acidocaldarius showing immunological cross-reactivity with the Kdp system from Escherichia coli.

During growth with low levels of K+, Bacillus acidocaldarius expressed a high-affinity K+ uptake system. The following observations indicate that this system strongly resembles the Kdp-ATPase of Escherichia coli: (i) its high affinity for K+ (Km of 20 microM or below); (ii) its poor transport of Rb+; (iii) the enhanced ATPase activity of membranes derived from cells grown with low levels of K+ (this activity was stimulated by K+ and inhibited by vanadate); (iv) the expression of an extra protein with a molecular weight of 70,000 in cells grown with low levels of K+; and (v) the immunological cross-reactivity of this 70,000-molecular-weight protein with antibodies against the catalytic subunit B of the E. coli Kdp system. Antibodies against the complete E. coli Kdp system, which immunoprecipitated the whole E. coli KdpABC complex, almost exclusively precipitated the 70,000-molecular-weight protein from detergent-solubilized B. acidocaldarius membranes. The possibility that the B. acidocaldarius Kdp system consists of a single, KdpB-type subunit is discussed.

Adenosine Triphosphatases↗
PubMed1985

Binocular luminance summation in infants. A test for stereopsis?

The difference in pupil diameter between monocular and binocular viewing conditions has been found to be significantly different in human infants at an age of onset that is positively correlated with the age of onset for stereopsis. We attempted to use this information on binocular luminance summation (BLS) to devise a simple objective test using a direct ophthalmoscope in a modified two-part swinging-flashlight test. We evaluated 67 subjects with varying degrees of known heterotropia ranging in age from 16 hours to 20 years in an effort to determine a threshold measure of stereo-acuity or degree of heterotropia at which the test result might reproducibly change. We found BLS to be normally absent until about 4 months of age. All subjects older than 4 months manifested summation regardless of the extent of heterotropia, thus making our test unusable. We conclude that BLS is more than an ipsilateral consensual pupillary response, and we concur with others that these visual pathways must undergo maturation beyond the time of birth.

Adolescent↗
PubMed1985

Generation of a large, protonophore-sensitive proton motive force and pH difference in the acidophilic bacteria Thermoplasma acidophilum and Bacillus acidocaldarius.

The mechanism by which acidophilic bacteria generate and maintain their cytoplasmic pH close to neutrality was investigated. For this purpose we determined the components of proton motive force in the eubacterium Bacillus acidocaldarius and the archaebacterium Thermoplasma acidophilum. After correction for probe binding, the proton motive force of untreated cells was 190 to 240 mV between external pH 2 and 4. Anoxia diminished total proton motive force and the transmembrane pH difference by 60 to 80 mV. The protonophore 2,4-dinitrophenol abolished the total proton motive force almost completely and diminished the transmembrane pH difference by at least two units. However, even after correction for probe binding, protonophore-treated cells maintained a pH difference of approximately one unit.

2,4-Dinitrophenol↗
PubMed1984

Results from a simple laser color perimeter.

Stimulus size, chromaticity, adaptation, luminance and local adaptation are more easily controlled when laser light rapidly scans the appropriate portion(s) of the visual field. Adaptation of a Ferree-Rand perimeter to the use of He-Ne laser light gives chromatic and achromatic thresholds of relatively low variance.

Adaptation, Ocular↗
PubMed1981

The mechanism of uncoupling by picrate in Escherichia coli K-12 membrane systems.

The mechanism of action of the uncoupler picrate on intact cells and everted membrane vesicles of Escherichia coli K-12 was investigated. Like in mitochondria [Hanstein, W. G. and Hatefi, Y. (1974) Proc. Natl Acad. Sci. USA, 71, 288-292], it was observed that picrate uncoupled energy-linked functions only in everted, but not in intact membrane systems. In the vesicles picrate also decreased the magnitude of the transmembrane proton-motive force at concentrations similar to those at which it caused uncoupling. Experiments with 14C-labelled picrate showed that this compound bound both to deenergized intact cells and everted vesicles. However, upon energization of the membrane, picrate was extruded from the intact cell and taken up to a larger extent by the vesicles. These energy-dependent changes in picrate uptake correlated with the magnitude of the transmembrane electrical potential, delta psi. It is therefore proposed that picrate is a permeant uncoupler, that delta psi is the driving force for picrate movement across biological membranes, and that the uncoupling activity of picrate in everted membrane systems is due to its protonophoric action.

Adenosine Triphosphate↗
PubMedDate not supplied

Operating microscope-induced retinal phototoxicity: pathophysiology, clinical manifestations and prevention.

Retinal light damage is a poorly understood phenomenon, due to its multifactorial etiology and relatively infrequent recognition. It has been increasingly identified following ocular surgery involving the intense light of the operating microscope. The authors describe the clinical entity, review salient features of its pathophysiology and provide guidelines for prevention of retinal phototoxicity.

Animals↗
PubMedDate not supplied

[Acoustically evoked brain magnetic activity in normal and growth retarded fetuses during the third trimester of pregnancy].

The fetal magnetoencephalogram with a 31 chanal biomagnetometer made by Philips was measured in a fetal 1F-phase in 20 normotroph unimpaired and in 14 growth retarded fetuses with a birth weight < 5 percentile after completed 36th gestational week. Trough defined acoustic stimulations, which were applied over the maternal abdominal wall, it was possible to measure acoustic evoked cerebromagnetic field changes using a special computer programs. The registrated evoked cerebromagnetic field changes had a latence time of 112.8 +/- 18.4 ms in normotroph fetuses and 130.9 +/- 18.5 ms in hypotroph fetuses. The difference was significant (p < 0.01). The presented results lead to the conclusions that the fetal magnetoencephalography makes a differentiation between normal and disturbed fetal cerebral integrity possible.

Embryonic and Fetal Development↗