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C Richter

Publications and source records attributed to C Richter.

At least 145 records · Page 8Linked to original sources
PubMed1992

Prooxidant-induced Ca2+ release from liver mitochondria. Specific versus nonspecific pathways.

Ca2+ release from mitochondria can be induced by a variety of chemically different prooxidants. Release induced by these compounds is possibly regulated by protein mono(ADP)ribosylation, and leaves mitochondria initially intact. Excessive "cycling" (continuous release and uptake) of Ca2+ by mitochondria leads to their damage, as shown by a decreased membrane potential, fast Ca2+ release, and impairment of ATP synthesis. When cycling is prevented by Ca2+ chelators or by inhibition of the uptake route with ruthenium red, prooxidants still induce Ca2+ release but mitochondria remain intact. It has recently been suggested that formation of a "pore" in the inner mitochondrial membrane participates in the Ca2+ release mechanism. We find that the prooxidant-induced Ca2+ release is not paralleled by sucrose entry into, or K+ release from, or swelling of mitochondria, provided Ca2+ cycling is prevented. Thus, the prooxidant-induced Ca2+ release does not require formation of a "pore." We conclude that the release occurs via a specific pathway.

Animals↗
PubMed1992

'Pore' formation is not required for the hydroperoxide-induced Ca2+ release from rat liver mitochondria.

It has recently been suggested by several investigators that the hydroperoxide- and phosphate-induced Ca2+ release from mitochondria occurs through a non-specific 'pore' formed in the mitochondrial inner membrane. The aim of the present study was to investigate whether 'pore' formation actually is required for Ca2+ release. We find that the t-butyl hydroperoxide (tbh)-induced release is not accompanied by stimulation of sucrose entry into, K+ release from, and swelling of mitochondria provided re-uptake of the released Ca2+ ('Ca2+ cycling') is prevented. We conclude that (i) the tbh-induced Ca2+ release from rat liver mitochondria does not require 'pore' formation in the mitochondrial inner membrane, (ii) this release occurs via a specific pathway from intact mitochondria, and (iii) a non-specific permeability transition ('pore' formation) is likely to be secondary to Ca2+ cycling by mitochondria.

Animals↗
PubMed1992

In vivo modulation of total and mitochondrial glutathione in rat liver. Depletion by phorone and rescue by N-acetylcysteine.

The aim of the present work was to modulate in vivo the level of hepatic mitochondrial glutathione (GSH). Rats were given phorone (diisopropylidene acetone), which in vivo becomes enzymatically conjugated to GSH, and were subsequently treated with N-acetylcysteine (NAC) to rescue GSH. In liver homogenate, a rapid and biphasic (T1/2 less than or equal to 15 min and 1.5 hr) drop of GSH was observed upon phorone administration. NAC treatment led to a restoration (T1/2 about 1 hr) of GSH in the homogenate above control values within 3 hr. The mitochondrial GSH level decreased with T1/2 of about 1.5 hr upon phorone treatment, and was 75% restored by NAC treatment within 3 hr. Hydroperoxide-induced mitochondrial pyridine nucleotide oxidation and Ca2+ release were impeded in GSH-depleted organelles, and NAC treatment restored these processes. The GSH status had no influence on mitochondrial pyridine nucleotide oxidation and Ca2+ released induced by alloxan, which reacts directly and non-enzymatically with pyridine nucleotides. It is concluded that NAC is able to rescue mitochondrial GSH in vivo and restore important mitochondrial functions. The data suggest that NAC may be a useful antidote in oxidative stress-related diseases.

Acetylcysteine↗
PubMed1992

Reactive oxygen and DNA damage in mitochondria.

During the last decade the importance of reactive oxygen species as major contributors to various types of cancer, heart diseases, cataracts, Parkinson's and other degenerative diseases that come with age, and to natural aging has become apparent. Mitochondria are the most important intracellular source of reactive oxygen. Mitochondrial DNA is heavily damaged by reactive oxygen at the bases, as indicated by the high steady-state level of 8-hydroxydeoxyguanosine, the presence of which causes mispairing and point mutations. Mitochondrial DNA is also oxidatively fragmented to a certain extent. Conceivably, such fragmentation relates to deletions found in mitochondrial DNA. Point mutations and deletions have recently been shown to be etiologically linked to several human diseases and natural aging. Future studies should address the causal relationship between mitochondrial dysfunction, production of reactive oxygen species, and aging.

Aging↗
PubMed1992

Herpes zoster as an indicator of HIV infection in Africa.

In areas where resources for health information are limited, the incidence of herpes zoster can usefully be monitored as an indicator of HIV infection. A sudden parallel rise of the number of symptomatic HIV cases and herpes zoster cases was observed in a northern district of Zimbabwe. Herpes zoster was made locally reportable. Three years later the incidence of herpes zoster and HIV in the hospital and of herpes zoster in the surrounding rural health centres was analysed. The herpes zoster attack rate and the HIV seropositivity rate of herpes zoster patients resembled those elsewhere in Africa. The distribution of cases of zoster was comparable with that of HIV infection.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Pattern of HIV-infection in Hurungwe district, Mashonaland West, Zimbabwe.

After the first case of HIV-infection had been diagnosed in 1986 in a Northern district of Zimbabwe, a local hospital based surveillance system, was introduced. In order to monitor the spread of the epidemic in the district, residence, age, sex and clinical presentation of all newly diagnosed HIV-patients were recorded. After three years, the data were compiled and analysed with the following results. Altogether 887 symptomatic HIV-patients (0.5 pc of the district population) were diagnosed. The most common HIV-associated signs and symptoms were PGL (47 pc), chest infection (29 pc), herpes zoster (24 pc) and chronic STDs (15 pc). The female-to-male ratio in adults was 1.4. The average age on diagnosis in women was 26.0 +/- 6.7 years and in men 30.7 +/- 8.6 years. The three years' cumulative incidence of HIV-cases was 27.2/1,000 in the urban area and 3/1,000 in the rural areas of the district.

Adolescent↗
PubMed1991

Isoelectric focusing of cytochrome P450: isolation of six phenobarbital-inducible rat liver microsomal isoenzymes.

A procedure for the isolation of native proteins from membranes by isoelectric focusing is described. It was used to resolve into six components the major fraction of cytochrome P450, obtained from liver microsomes of phenobarbital-treated rats, after chromatography on DE-52 cellulose. When eluted from the gel, these proteins are in a native form as shown by (a) the light absorption spectra of the Soret region of their reduced carbonyl derivatives, all characterized by maxima around 450 nm, and (b) their enzymatic activities toward three different substrates. Characterization by a monoclonal antibody and partial sequence analysis of tryptic peptides reveal that three of the IEF-purified proteins have P450IIB1 character, whereas the other three are related to P450IIB2.

Amino Acids↗
PubMed1991

Inhibition by cyclosporine A of the prooxidant-induced but not of the sodium-induced calcium release from rat kidney mitochondria.

The use of the immunosuppressive drug cyclosporine A (CSA) is restricted by its nephrotoxicity. Perturbation of Ca2+ homeostasis has been implicated in chemical toxicity. Mitochondria, a key regulator of Ca2+ homeostasis, may be a target of the drug. Here we show that CSA inhibits at low concentrations the prooxidant-induced but not the sodium-induced Ca2+ release from rat kidney mitochondria. CSA does not affect Ca2+ uptake by mitochondria. Inhibition of Ca2+ release is due to inhibition of intramitochondrial enzymatic hydrolysis of NAD+ to ADP-ribose and nicotinamide. These findings suggest a very specific effect of CSA on mitochondrial Ca2+ release by which the drug interferes with cellular Ca2+ homeostasis. This is possibly the basis of CSA nephrotoxicity.

Adenosine Diphosphate Ribose↗
PubMed1991

Rotation and interaction with epoxide hydrase of cytochrome P-450 in proteoliposomes.

Purified rat liver cytochrome P-450MC or P-450PB was co-reconstituted with epoxide hydrase in liposomal vesicles made of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine at a lipid to protein weight ratio of 5 by the cholate dialysis procedure. Rotational diffusion of the cytochromes was measured by observing the decay of absorption anisotropy, r(t), after photolysis of the heme.CO complex by a vertically polarized laser flash. Analysis of r(t) was based on a "rotation-about-membrane-normal" model. The measurements were used to investigate interactions of cytochrome P-450MC or P-450PB with epoxide hydrase. Different rotational mobilities of the two cytochromes were observed. The amount of mobile molecules was 78% for cytochrome P-450MC and 91% for P-450PB, and the rest was immobile within the experimental time range of 1 ms. In the presence of epoxide hydrase 85% of cytochrome P-450MC and 96% of P-450PB were mobile. Cross-linking of epoxide hydrase by anti-epoxide hydrase antibodies resulted in a drastic immobilization of the cytochromes, reducing the mobile population to 49% for P-450MC and to 60% for P-450PB. The rotational relaxation times phi of the mobile populations ranged from 210 to 283 microseconds. These results imply that both cytochromes P-450MC and P-450PB transiently associate with epoxide hydrase in liposomal membranes. Further analysis of the data showed that the angle between the heme plane of P-450MC and the membrane is 48 degrees or 62 degrees, different from the value of 55 degrees reported previously for P-450PB (Gut, J., Richter, C., Cherry, R. J., Winterhalter, K. H., and Kawato, S. (1983) J. Biol. Chem. 258, 8588-8594).

Animals↗
PubMed1991

Chemical modification of rat liver microsomal cytochrome P-450: study of enzymic properties and membrane topology.

Isolated rat liver cytochrome P-450IIB1 was alkylated and acetylated at primary amino groups, and the position of the modified amino acids in the protein was identified. Alkylation of up to nine amino groups did not disturb the interaction of reconstituted P-450 and NADPH-cytochrome-P-450 reductase in a way that hydroxylation of benzphetamine was altered, whereas deethylation of 7-ethoxycoumarin was gradually reduced in parallel with impaired 7-ethoxycoumarin binding. Acetylation of four lysine residues completely inhibited binding and metabolism of 7-ethoxycoumarin but not of benzphetamine. These results suggest the presence of different substrate binding sites on P-450. Exhaustive proteolysis of modified P-450 in proteoliposomes liberated all but the N-terminal modified peptide and 85 to 90% of the cytochrome's mass from intact proteoliposomes. These findings further support our previously proposed model of P-450 topology (Vergères, G., Winterhalter, K.H. and Richter, C. (1989) Biochemistry 28, 3650-3655), in which P-450 is anchored to the membrane with the N-terminal peptide only, the N-terminal methionine facing the lumenal interior.

Alkylation↗
PubMed1991

Localization of the N-terminal methionine of rat liver cytochrome P-450 in the lumen of the endoplasmic reticulum.

Recent cumulative evidence suggests that liver microsomal cytochrome P-450 (P-450) is exposed to the cytosol with the exception of the N-terminal peptide (amino acid residues 1 to 21), or two peptides (residues 1 to 60). We tested the localization of the N-terminal methionine residue of P-450IIB1 of rat liver microsomes in the natural membrane with the site-specific reagent fluorescein isothiocyanate. The N-terminus of isolated P-450 was stoichiometrically modified in solution with fluorescein isothiocyanate. In intact microsomes, the N-terminus was not modified but became accessible to the reagent when the membrane was dissolved with Triton X-100. Our results indicate that the N-terminus faces the lumen of the endoplasmic reticulum, and we propose that P-450 spans the membrane only once with amino acid residues 1 to 21.

Animals↗
PubMed1991

Oxidative stress in mitochondria: its relationship to cellular Ca2+ homeostasis, cell death, proliferation, and differentiation.

A variety of chemically different prooxidants causes Ca2+ release from mitochondria. This prooxidant-induced Ca2+ release occurs from intact mitochondria via a route which is physiologically relevant and may be regulated by protein monoADP-ribosylation. When the released Ca2+ is excessively 'cycled' by mitochondria (continuously taken up and released) the inner membrane is damaged. This leads to a decreased ability of mitochondria to retain Ca2+, uncoupling of mitochondria, and an impairment of ATP synthesis, which in turn deprives the cell of the energy necessary for the proper functioning of the Ca2+ ATPases of the endoplasmic (sarcoplasmic) reticulum, the nucleus and the plasma membrane. The ensuing rise of the cytosolic Ca2+ level cannot be counterbalanced by the damaged mitochondria which, under normoxic conditions, act as a safety device against an increase of the cytosolic Ca2+ concentration. The impaired ability of mitochondria to retain Ca2+ may lead to cell death. However, there is also evidence emerging that release of Ca2+ from mitochondria may be physiologically important for cell proliferation and differentiation.

1-Methyl-4-phenylpyridinium↗
PubMed1991

Continuously active sodium channels in osteoblastic ROS 17/2.8 cells.

Cell-attached patch clamp experiments revealed 13-20 pS Na(+)-conducting channels active at normal resting potentials (-28 +/- 1 mV; +/- SEM; 7 cells) in the rat osteosarcoma cell line, ROS 17/2.8. These channels were not blocked by tetrodotoxin, Cd2+, verapamil, or nifedipine. Replacing all cations in the patch pipette except Ca2+ with tetraethylammonium (TEA+) abolishes channel activity; but adding TEA+ to a pipette solution containing only Na+ does not. Depolarization was not necessary to activate these channels, and the open times were much longer than the millisecond open times characteristic of Na+ channels in excitable cells. Current-voltage curves reconstructed from mean single channel currents and mean channel open times resemble L-type Ca2+ current-voltage curves obtained from whole-cell experiments, with current peaks shifted to resting or more hyperpolarized potentials. The voltage sensitivity of these channels has implications on membrane potential stability and on the hyperpolarizing membrane potential spiking activity exhibited by ROS 17/2.8 cells.

Animals↗
PubMed1991

Enzyme-linked immunosorbent assay using monoclonal antibodies for identification of mycobacteria from early cultures.

A simple enzyme-linked immunosorbent assay (ELISA) for the identification of cultured mycobacteria belonging to the Mycobacterium tuberculosis complex, the Mycobacterium avium complex, and Mycobacterium kansasii has been developed (R. Schöningh, C. P. H. J. Verstijnen, S. Kuijper, and A. H. J. Kolk. J. Clin. Microbiol. 28:708-713, 1990). The test for the routine identification of cultured mycobacteria was introduced in five clinical laboratories located in Tanzania, Thailand, Vietnam, and The Netherlands. The ELISA can be conducted without an ELISA reader since the test can be read visually. The results of identification of 255 strains of the M. tuberculosis complex by microbiological means and by ELISA were compared; the specificity and the sensitivity were 100%. For the M. avium complex, the specificity was 100% and the sensitivity was 64%. All 26 M. kansasii strains tested could be identified as M. kansasii. The ELISA described here proved to be useful in both well- and modestly equipped laboratories and may replace the microbiological method of identification of M. tuberculosis and M. kansasii.

Antibodies, Monoclonal↗
PubMed1991

An experimental test of a model for repeated Ca2+ spikes in osteoblastic cells.

A model for cytosolic Ca2+ spikes is presented that incorporates continual influx of Ca2+, uptake into an intracellular compartment, and Ca(2+)-induced Ca2+ release from the compartment. Two versions are used. In one, release is controlled by explicit thresholds, while in the other, release is a continuous function of cytosolic and compartmental [Ca2+]. Some model predictions are as follows. Starting with low Ca2+ influx and no spikes: (1) induction of spiking when Ca2+ influx is increased. Starting with spikes: (2) increase in magnitude and decrease in frequency when influx is reduced; (3) inhibition of spiking if influx is greatly reduced; (4) decrease in the root-mean-square value when influx is increased; and (5) elimination of spiking if influx is greatly increased. Since there is good evidence that hyperpolarizing spikes reflect cytosolic Ca2+ spikes, we used electrophysiological measurements to test the model. Each model prediction was confirmed by experiments in which Ca2+ influx was manipulated. However, the original spike activity tended to return within 5-30 min, indicating a cellular resetting process.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1991

Antibodies against central nervous system tissue (anti-CNS) detected by ELISA and western blotting: marker antibodies for neuropsychiatric manifestations in connective tissue diseases.

Organ specific antibodies against epitopes of the central nervous system (CNS) tissue were detected by ELISA and Western blotting (WB) in sera from patients with ANA positive collagen disorders using a 100,000 g supernatant from beef or rat brain. The corresponding CNS-antigens consist of six major determinants at molecular weights 29, 48, 56, 68 kD and six minor determinants at 130, 110, 86, 60, 38, 34 kD. All except the 38 kD polypeptide were organ specific. Forty-six of 91 patients with ANA positive collagen disorders reacted with at least one of these determinants; 43 of them had cerebral symptoms in contrast to only three of the 43 anti-CNS negative patients. Sera from patients with other disorders did not react with these epitopes. We conclude that anti-CNS antibodies detected by Western blotting may be marker for neuropsychiatric manifestations in patients with collagen disorders.

Adolescent↗