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Biomedical subjects

E Neumann

Publications and source records attributed to E Neumann.

At least 163 records · Page 9Linked to original sources
PubMed1976

Dynamic properties of isolated acetylcholine receptor proteins: release of calcium ions caused by acetylcholine binding.

Interaction of Ca and acetylcholine (AcCh) ions with purified acetylcholine receptor (AcChR) from Torpedo californica and Electrophorus electricus has been investigated in view of these ions' role proposed in bioelectricity. Spectrophotometric Ca titration using murexide as an indicator and an ultrafiltration method with 45Ca show that AcChR proteins have a high binding capacity for Ca ions. Per macromolecule of 260,000 daltons, up to 60 Ca ions can be bound with at least three Ca dissociation constants. A linear inhibition of AcCh binding to AcChR by Ca was observed in the 0.1-1 mM Ca range, indicating competition of AcCh and Ca for AcChR. The addition of AcCh to a Ca-AcChR solution at 1.2 mM Ca causes release of four to six bound Ca ions from AcChR when a maximum of two AcCh ions are bound per 260,000 dalton macromolecule. The subsequent addition of alpha-bungarotoxin causes reuptake of up to six Ca ions by AcChR. These results suggest that the neural activator AcCh and the inhibitor alpha-bungarotoxin induce opposing shifts between different conformational states of isolated AcChR.

Acetylcholine↗
PubMed1976

Dynamic properties of isolated acetylcholine receptor protein: kinetics of the binding of acetylcholine and Ca ions.

Kinetic and thermodynamic constants for elementary steps associated with the interaction of acetylcholine (AcCh) and Ca with isolated AcCh receptor from Torpedo californica have been determined by chemical relaxation spectrometry. Murexide as used as a Ca indicator to monitor changes in Ca bound to the AcCh receptor. In the presence of AcCh this technique permits an indirect monitoring of AcCh binding, because the AcCh and the Ca binding reactions are competitively coupled. A temperature-jump perturbation in the Camurexide-AcCh receptor system induces a spectrum of relaxation processes characterized by at least three relaxation times: tau1 = 5 (+/-1) msec; tau2 = 35 (+/-5) msec; and tau3 = 300 (+/-30) msec. In the presence of AcCh, the Ca relaxation spectrum is altered in a characteristic way. A formalism is developed to describe the normal mode relaxation times of the coupled reaction system in terms of total concentrations of both AcCh and receptor binding sites. The analysis also allows one to determine the stoichiometry of the reactions involved or to estimate a molecular weight of the AcCh receptor. The kinetic data suggest that the reaction of AcCh with receptor proceeds in at least two steps. The rate constant of the association of AcCh with receptor was found to be 2.4(+/-0.5) X 10(7) M-1 sec-1 at 23.5 degrees, 0.1 M NaCl, 50 mM Tris-HCl, pH 8.5. Reaction schemes consistent with the present kinetic data are discussed in terms of physiocochemical model that accounts for the rapid transient conductivity changes in excitable membranes during nerve and muscle excitation.

Acetylcholine↗
PubMed1976

Physical-chemical approach to the transient change in Na ion conductivity of excitable membranes.

A new method is proposed for analyzing the rapid transient current component (Na ions) in voltage clamp experiments on excitable membranes. The method is based on only two very general assumptions: the Na ion conductivity of an excitable membrane is determined by some general membrane parameter, the kinetic behavior of which is consistently described by the sum of only two simple exponential terms. A least square computer analysis for the data by L. Goldman and C.L. Schauf on Myxicola axons is described [(1973) J. Gen. Physiol. 61, 361-384]. The method gives (as a result) the relationship between conductivity and membrane parameter. A physically plausible, chemical model (cycle of three states) is proposed for a dissipative control of the Na ion conductivity. The rate constants for the specific model are calculated from kinetic parameters derived only from the general analysis. These rate constants reproduce the original voltage clamp data in every feature which includes peak current ratios (h infinity)-shift with test potential. By allowing for differences in the experimental conditions, we derive essentially the same rate constants for the voltage clamp data of A.L. Hodgkin and A.F. Huxley on squid giant axons.

Action Potentials↗
PubMed1976

[Efficiency of revascularization of the liver by intra-hepatic implantation of the splenic vascular pedicle].

Experiments carried out in 12 dogs with ligature of the hepatic lobar artery, show that intra-hepatic implantation of the splenic artery, or vascular pedicle, offers limited revascularisation. This produces a fall in blood flow in the implanted artery, reduction in glycogen and hepatic A.T.P., associated with a fall in the total protein content and hepatosine. At the same time, although there is a rich network of neoformed vessels, the hepatic transaminase and lactate activities undergo a pronounced rise.

Adenosine Triphosphate↗
PubMed1975

[Vasculitis nodularis with participation of inner organs].

The vasculitis nodularis belongs to the group of the allergic-hyperergic vascular diseases of the skin, which above all the small veins are affected at. The participation of internal organs is unusual. It is reported on a 31-year-old Syrian patient in whom a participation of the liver in form of a granulomatous hepatitis and of the kidneys appeared. A hypertension might be attributed to the participation of the kidneys. The incorporation of a thrombosis of the central vein of the right eye in this disease is probable. The main symptoms of the disease were nodes of the size of a bean occurring in batches, lying subcutaneously, and were paraclinical signs for inflammation. The permanently increased absorption-antistreptolysin titre spoke for an allergic-hyperergic vascular process induced by streptococci.

Adult↗
PubMed1975

Effect of retinal detachment surgery on the course of preexisting open-angle glaucoma.

In 11 of 12 eyes with chronic simple glaucoma after surgery for retinal detachment, intraocular pressures were decreased for one to 5 1/2 years without any antiglaucomatous treatment. No further deterioration in the state of the optic disks or the visual fields occurred in any of these eyes. In all 12 fellow eyes antiglaucomatous treatment is still being administered. The operation employed in nine of the 11 cases consisted of an encircling silicone rubber band shortened by 15 to 20% of its length when placed around the eyeball before tapping subretinal fluid. An episcleral silicone implant was placed under the encircling ban in seven of these eyes. Kinking and possibly narrowing of the long posterior ciliary arteries by the encircling silicone band probably caused the ciliary hyposecretion and the resultant hypotony.

Aged↗
PubMed1975

Ionic strength dependence of the hysteresis in the polyriboadenylate-polyribouridylate system.

The hysteresis observed in cyclic acid-base titrations of the three-standed polyribonucleotide helix poly (A)-2 POLY (U) strongly depends on ionic strength. For NaCl and at 25 degrees C, hysteresis occurs in the limited concentration range between 0.03 M and 1.0 M(NaCl). The transition points associated with the cyclic conversions between the triple helix and the poly (A)-poly (A) double helix and (free) poly (U) constitute a (pH ionic strength) phase diagram covering the ranges of stability and metastability of the hysteresis system. Variations with NaCl concentration of some hysteresis parameters can be quantitatively described in terms of polyelectrolyte theories based on the cylinder-cell model for rodlike polyions. The results of this analysis suggest that the metastability is predominantly due to dlectrostatic energy barriers preventing the equilibrium transition of the partially protonated triple helix above a critical pH value. Ultraviolet absorbance and potentiometric titration data of poly (A)in the acidic pH range can be analyzed in terms of two types of double-helical structures. Spectrophotometric titrations reveal isosbestic wavelengths for structural transitions of poly (A). "Time effects" commonly observed in poly (A) titrations are suggested to reflect helix transitions between the two acidic structures.

Adenine Nucleotides↗
PubMed1975

[Angiography, scintigraphy and ultra sound in the diagnosis of splenic or hepatic disease in Hodgkin's disease (author's transl)].

The combined use of selective angiography, scintigraphy and ultra-sound is not reliable enough for the certain exclusion of visceral involvement in Hodgkin's disease. Since this is of importance in the planning of treatment, it confirms the recommendation made by Wagenknechts, Glatsteins and others that a diagnostic splenectomy be carried out in order to determine the presence of visceral involvement.

Adolescent↗
PubMed1975

Posterior vitreous detachment after cataract extraction in non-myopic eyes and the resulting retinal lesions.

A series of 54 non-myopic aphakic eyes with no signs of posterior vitreous detachment and 63 non-myopic aphakic eyes with various stages of posterior vitreous detachment was followed-up for a period of 6 months to 6 years. Over half of the eyes with no vitreous detachment when first examined developed various stages of posterior vitreous detachment during the follow-up period; in 10 eyes this was accompanied by entopsies with or without photopsies and three eyes developed five new retinal tears. In over half of the eyes with partial vitreous detachment when first examined, the vitreous detachment continued to progress causing retinal detachment in one eye. Late vitreous detachment in non-myopic aphakia or the completion of a partially-detached vitreous could account for the higher incidence of retinal tears in this group of eyes.

Aged↗
PubMed1975

Myopia-aphakia. I. Prevalence of retinal detachment.

Retinal detachment after cataract extraction occurred in nine out of 136 eyes with myopia of 6 or more dioptress (6-7 per cent), during a follow-up period of 1 1/2-9 1/2 years. Five of the nine detachments occurred within 3 months of cataract extraction. All patients with retinal detachment were under the age of 63 years. Relatively young patients with high myopia bear a special risk of developing retinal detachment after lens extraction. The possible reason for this is discussed.

Age Factors↗
PubMed1975

Myopia-aphakia. II. Vitreous and peripheral retina.

Biomicroscopical examination of the vitreous and peripheral retina was performed on 103 aphakic eyes with myopia of at least -6-0 dioptres. Retinal breaks were found in 19 eyes (18-4 per cent). Posterior vitreous detachment was present in all but one of the eyes. The high prevalence of retinal breaks in aphakic eyes with high myopia is compatible with the high incidence of retinal detachment in such eyes.

Adult↗