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Biomedical subjects

H Michel

Publications and source records attributed to H Michel.

At least 343 records · Page 19Linked to original sources
PubMed1980

Electrochemical proton gradient across the cell membrane of Halobacterium halobium: effect of N,N'-dicyclohexylcarbodiimide, relation to intracellular adenosine triphosphate, adenosine diphosphate, and phosphate concentration, and influence of the potassium gradient.

The proton motive force across the cell membrane of halobacterial cells has been estimated and compared to intracellular values of ATP, ADP, and inorganic phosphate concentrations with respect to the chemiosmotic hypothesis. The accumulation of 14C-labeled indicator substances, triphenylmethylphosphonium for the membrane potential and 5,5-dimethyloxazolidine-2,4-dione for the pH difference between the cell interior and the medium, has been measured in the cells. Values up to 270 mV for the proton motive force have been found in cells pretreated with N,N'-dicyclohexylcarbodiimide (DCCD, 10(-4) M, 30 degrees C, 12 h). Upon illumination a high membrane potential is generated, which is then gradually replaced by a large pH difference. Cells treated with lower DCCD concentrations show only an enhancement of membrane potential upon illumination; the pH difference remains at a low level. Under anaerobic dark conditions, untreated cells maintain a proton motive force of 120-140 mV, which is equilibrated with the intracellular levels of ATP, ADP, and inorganic phosphate. The pH gradient is 1 unit at pH 6 but 0 at pH 8. The membrane potential is low (60-80 mV) at pH 6 and high (120-130 mV) at pH 8. We propose that the proton translocating ATPase compensates for the lowered pH difference at high external pH values by enhancing the membrane potential. The concentration difference of the potassium ions influences the proton motive force and the intracellular ATP levels, apparently via its action on the membrane potential. When the difference of the chemical potential of the potassium ion, expressed in millivolts, exceeds the preexisting membrane potential, the intracellular ATP level is enhanced. When the difference of the chemical potential of the potassium ion (millivolts) is smaller than the membrane potential, the ATP level is decreased.

Adenosine Diphosphate↗
PubMed1980

Electrochemical proton gradient across the cell membrane of Halobacterium halobium: comparison of the light-induced increase with the increase of intracellular adenosine triphosphate under steady-state illumination.

The increase of the proton motive force mediated by bacteriorhodopsin is compared to the intracellular ATP concentration under steady-state illumination. The membrane potential was measured via the accumulation of the lipophilic ion [14C]triphenylmethylphosphonium and the pH gradient via the accumulation of the weak acid 5,5-dimethyloxazolidine-2,4-dione. Light causes a parallel increase of ATP level and membrane potential at an external pH of 8. In contrast, at pH 6 an increase of the intracellular ATP concentration occurs without a corresponding increase of the proton motive force. If the extracellular NaCl concentration is reduced and not replaced by other ions, no membrane potential at all can be measured at pH 6-7; nonetheless, light-induced ATP synthesis occurs. A significant enhancement of the pH gradient occurs only at irradiances higher than those required for the attainment of the maximal intracellular ATP concentration. In the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone it is possible to obtain light-induced ATP synthesis without a measurable proton motive force in basal salt at pH 8. It is concluded that if bacteriorhodopsin acts as a proton pump, then the pumped protons can be used for ATP synthesis before they equilibrate with the protons in the extracellular bulk phase.

Adenosine Diphosphate↗
PubMed1980

Orthorhombic two-dimensional crystal form of purple membrane.

A new two-dimensional crystal form of purple membrane has been obtained in vitro. It is produced by the joint use of a cationic detergent, dodecyltrimethylammonium chloride, and the nonionic detergent, Triton X-100. It primarily forms large, rolled-up sheets that look like needles in the light microscope. Liposomes and tubes are also observed. The absorption maximum of the new form of purple membrane is blue-shifted by 6 nm and its density is slightly lower than the natural form of purple membrane. The new form of purple membrane is orthorhombic with space group p22121 and cell dimensions 57.6 x 73.5 A. Four molecules of bacteriorhodopsin occupy the unit cell with an area per molecule close to that found in the native p3 structure. The projected structure to 6.5-A resolution was determined by electron microscopy and diffraction. It shows an identical molecular structure to that of the p3 form and determines the position of the polypeptide boundary.

Bacteriorhodopsins↗
PubMed1980

Three-dimensional crystals of membrane proteins: bacteriorhodopsin.

The intrinsic membrane protein bacteriorhodopsin has been crystallized by salt precipitation after solubilization by octyl glucoside. Two different crystal forms were obtained, depending on the nature of the salt used and the pH. Needles formed in the presence of sodium phosphate and in ammonium sulfate solutions above pH 4.8. Cubes appeared in sodium citrate solutions or ammonium sulfate. Unlike the cubic crystals, the birefringent needles showed strong linear dichroism, which allowed determination of the orientation of the chromophore's transition moment. The procedure described here may be of general use in crystallographic studies of membrane proteins.

Bacteriorhodopsins↗
PubMed1980

Changes in brain catecholamine levels in human cirrhotic hepatic encephalopathy.

Hepatic encephalopathy (HE) is currently felt to be secondary to a disturbance in the metabolism of cerebral catecholamines with a decline in dopamine and noradrenaline and a rise in the false neurotransmitter octopamine. The aim of this study was to evaluate brain tissue levels of dopamine, noradrenaline, and octopamine in patients with cirrhosis and HE. This study includes 34 patients: 22 were cirrhotic, 12 were control subjects. Among the 22 cirrhotic patients, 19 had HE, three did not. Tissue specimens were obtained at necropsy from the locus niger, caudate nucleus, hypothalamus, thalamus and frontal cortex, and from the frontal cortex during neurosurgical procedures. Our results showed that (1) dopamine and noradrenaline levels are identical in cirrhotic patients with or without HE and in patients without liver disease (P < 0.05); (2) octopamine levels are higher in control subjects than in patients with cirrhosis and HE. In conclusion, there is no decline in dopamine and noradrenaline levels in the brain tissues of cirrhotic patients with HE, and this is in contradication with the animal findings; octopamine levels are not raised. Hepatic encephalopathy in human liver cirrhosis does not seem to be secondary to a disturbance in cerebral catecholamines.

Brain↗
PubMed1980

Treatment of cirrhotic hepatic encephalopathy with L-dopa. A controlled trial.

It has been suggested that hepatic encephalopathy could be due to the accumulation of false neurotransmitters and that the administration of a neurotransmitter precursor such as L-dopa would be beneficial to cirrhotic patients with hepatic encephalopathy. A prospective randomized controlled study was carried out to determine whether L-dopa has any effect on the course of cirrhotic hepatic encephalopathy. L-Dopa, L-Dopa and dopa-decarboxylase inhibitor, or placebo was given orally for 7 days to 75 cirrhotic patients with hepatic encephalopathy. The effect was assessed by clinical parameters as well as serial electroencephalograms. There was no statistically significant difference with respect to clinical improvement or deterioration in patients treated with either L-dopa or L-dopa and dopa-decarboxylase inhibitor or placebo. It is concluded that L-dopa is ineffective in the treatment of cirrhotic hepatic encephalopathy. Inefficacy was not due to late onset of treatment, to poor intestinal absorption of L-dopa, to destruction of L-dopa in the blood, or to impaired passage of L-dopa into the cerebrospinal fluid.

Adult↗
PubMed1979

[Thrombocytopenic purpura during heparinotherapy. Two cases (author's transl)].

In two patients treated by heparin for thrombosis, thrombocytopenia under 10 000/cumm occured accompanied with bleeding cud recurrent thrombosis. The demonstration in the patients' serum of a factor inducing platelet aggregation and serotonin release in the presence of heparin suggests that the thrombocytopenia could be of immuno-allergic origin. In both cases, the discontinuation of heparin resulted in clinical and biological improvement. The rare cases of heparin-induced thrombocytopenia reported in the literature are discussed.

Aged↗
PubMed1978

[Rupture of oesophagogastric varices: treatment by a new haemostatic tube (author's transl)].

The immediate arrest of haemorrhage due to ruptured oesophageal varices may be obtained only by the insertion of a haemostatic tube with a balloon. Tubes used up to the present time have been more or less discredited. Some authors consider the Sengstaken tube to be dangerous: rupture of oesophagus, asphyxia, bronchial inhalation of oesophageal secretions etc. The Lindon tube has a single grave disadvantage: cardio-oesophageal ulceration due to traction. The new tube would seem to be free of these problems since no traction is used and it is possible to suck out oesophageal secretions, thereby suppressing the risk of bronchial inhalation.

Esophageal and Gastric Varices↗