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Biomedical subjects

S Michel

Publications and source records attributed to S Michel.

At least 109 records · Page 6Linked to original sources
PubMed1993

The effects of lithium on a neuronal in vitro circadian pacemaker.

Previous studies have suggested a causal connection between abnormalities of the circadian system and affective disorders. The effectiveness of lithium or rubidium as a treatment for affective disorders and the ability of lithium or rubidium to influence circadian pacemakers has stimulated research into the mechanism of lithium's action on circadian systems. In this study we used a neuronal in vitro circadian pacemaker preparation, the eye of the mollusc Bulla, to examine the cellular effects of lithium and rubidium. Continuous extracellular LiCl application lengthens the period of the circadian rhythm of the Bulla pacemaker in a concentration-dependent manner. Rubidium was found to be more effective than lithium in period lengthening. Stable phase delays were generated by 2-h pulses of 395 mM LiCl applied extracellularly from zeitgeber time (ZT) 5-7 (mid subjective day). Concomitant continuous application of 16 mM LiCl and light (a depolarizing agent) generated period lengthening substantially greater than the arithmetic sum of the modest period lengthening of each treatment alone. Furthermore, LiCl pulses, applied together with depolarizing extracellular KCl concentrations, yielded an increasing magnitude of phase delays with increasing KCl concentration. These data suggest that LiCl acts intracellularly on the circadian pacemaker cells by entering through a voltage-dependent channel, most likely a sodium channel.

Animals↗
PubMed1992

Phase shifting of the circadian rhythm in the eye of Bulla by inhibition of chloride conductance.

Inhibition of Cl- conductance has been previously found to shorten the free-running period of the circadian eye rhythm of the marine snail Bulla gouldiana. In this study, we describe a phase-response curve for 6-h pulses of Cl(-)-free seawater, consisting only of phase advances with the largest in the late subjective night (1.5 h) and smaller phase shifts in the late subjective day. Intracellular recordings revealed that at both circadian times retinal pacemaker neurons hyperpolarized in response to the removal of extracellular chloride. Since previous studies indicate that membrane potential generates both phase advances and delays it seems unlikely that the action of chloride removal is mediated exclusively by the change in membrane potential.

Animals↗
PubMed1992

Evidence that potassium channels mediate the effects of serotonin on the ocular circadian pacemaker of Aplysia.

The eye of the marine mollusk Aplysia californica contains a photo-entrainable circadian pacemaker that drives an overt circadian rhythm of spontaneous compound action potentials in the optic nerve. Serotonin is known to influence the phase of this ocular rhythm. The aim of the present study was to evaluate whether potassium channels are involved in effects on the ocular circadian rhythm. Our experimental approach was to study the effect of the potassium channel antagonist barium on serotonin-induced phase shifts of this rhythm. The application of barium was found to block serotonin-induced phase shifts whereas barium alone did not cause significant phase shifts. The effects of barium were found to be dose dependent. In addition, barium blocked forskolin-induced phase advances but did not interfere with serotonin-induced increases in cAMP content. Finally, barium antagonized serotonin-induced suppression of compound action potential activity. These results are consistent with a model in which the application of serotonin phase shifts the ocular pacemaker by causing a membrane hyperpolarization which is mediated by a cAMP-dependent potassium conductance.

Action Potentials↗
PubMed1992

Quantitative correlation between the residual activity of beta-hexosaminidase A and arylsulfatase A and the severity of the resulting lysosomal storage disease.

A previously suggested model for the correlation between residual activity of a lysosomal enzyme and the turnover rate of its substrate(s) has been extended to a discussion of substrate accumulation rates in individual cells and whole organs. With these considerations, much of the observed variability in age of onset and clinical phenotype, as well as the phenomenon of pseudo-deficiency, can be understood as the consequences of small differences in the residual activity of the affected enzyme. In order to experimentally verify the basic assumptions on which this model rests, studies were performed in cell culture. The radiolabeled substrates ganglioside GM2 and sulfatide were added to cultures of skin fibroblasts with different activities of beta-hexosaminidase A or arylsulfatase A, respectively, and their uptake and turnover measured. In both series of experiments, the correlation between residual enzyme activity and the turnover rate of the substrate was essentially as predicted: degradation increased steeply with residual activity, to reach the control level at a residual activity of approximately 10-15% of normal. All cells with an activity above this critical threshold had a normal turnover. Comparison of the results of these feeding studies with the clinical status of the donor of each cell line basically confirmed our notions but also revealed the limitations of the cell culture approach.

Cells, Cultured↗
PubMed1992

Expression of keratinocyte transglutamine mRNA revealed by in situ hybridization.

Plasma membrane-bound transglutaminase (TGm) catalyzes the formation of cornified envelopes (CE) in terminally differentiating keratinocytes. The recent cloning of cDNA encoding rabbit TGm allows detailed studies of its gene expression and regulation. In the present paper, we describe the localization of TGm mRNA in rabbit tissues, as well as in normal and psoriatic human skin, as assessed by in situ hybridization. Furthermore, we correlate TGm mRNA localization with the distribution of the TGm protein detected by immunohistochemistry with a specific monoclonal antibody. In rabbit epidermis, TGm mRNA was expressed in suprabasal cells. The TGm protein was detected in the upper stratum spinosum and stratum granulosum. In rabbit esophagus, TGm mRNA and protein were already expressed to a high level in the first suprabasal cell layer, and their expression decreased in the more differentiated cells. In normal human skin, a small amount of TGm mRNA, restricted to the stratum granulosum, was found, whereas psoriatic skin samples contained high amounts of TGm mRNA in the suprabasal layers with a decreasing gradient into the rete ridges, i.e., the involutions of the epidermis into the dermal compartment. The TGm protein was absent from the rete ridges and confined to several cell layers expressing high levels of mRNA. There was virtually no difference between uninvolved psoriatic and normal epidermis.

Animals↗
PubMed1992

Differential expression of calgranulin A and B in various epithelial cell lines and reconstructed epidermis.

The monoclonal antibody F12, raised against epidermal cells from a psoriatic lesion, decorated antigens highly expressed in psoriatic epidermis and in cultured normal human keratinocytes. In normal human skin, F12 reacted only with follicular keratinocytes. Characterization of the immunoprecipitated antigens by two-dimensional gel electrophoresis revealed their identity with calgranulin A and B. A semiquantitative study with various established epithelial cell lines demonstrated that the expression of calgranulin A and B in hyperproliferative keratinocytes correlates with their potential to undergo terminal differentiation. In epidermis reconstructed in vitro, the antigen expression was stimulated by retinoids and suppressed under vitamin A starvation.

Antibodies, Monoclonal↗
PubMed1991

Intra- and inter-individual variations in cornified envelope peptide composition in normal and psoriatic skin.

Cornified envelopes from the stratum corneum of healthy volunteers and from the involved and uninvolved skin of psoriatic patients were electrophoretically purified, and their peptide composition analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS PAGE) after cyanogen bromide cleavage. The resulting envelope peptide patterns (EPPs) were compared. In normal subjects, mainly quantitative minor differences in the EPPs were observed between different individuals. In the same individual, palms and soles could be distinguished from other body sites by their EPPs. The palm and sole samples presented identical patterns which were different from the patterns found with samples from other body sites. In psoriatic patients, EPPs of uninvolved skin resembled closely those of healthy epidermis, but showed striking differences from those of lesional skin. The EPPs of psoriatic lesional skin showed a characteristic accumulation of small peptides with molecular weights of 3-11 kDa. The EPP of lesional skin returned to normal during PUVA therapy, indicating that the changes in the biochemical composition of the cornified envelope are correlated with the clinical status of the disease.

Adolescent↗
PubMed1991

Determination of retinoid activity by an enzyme-linked immunosorbent assay.

In normal human keratinocytes, retinoic acid suppresses the expression of the plasma membrane associated enzyme transglutaminase (TGm) at the pretranslational level. This finding led us to develop an enzyme-linked immunosorbent assay (ELISA) for the evaluation of the biological activity of retinoids, i.e., natural and synthetic derivatives of vitamin A. In this assay, keratinocytes are cultured in a 96-well cluster in the presence of different retinoid concentrations. The expression of TGm is then quantified, without any extraction or purification step, using a TGm-specific monoclonal antibody and a peroxidase-conjugated secondary antibody. The dose-response curves obtained show this ELISA to be a sensitive and reproducible assay to determine the potency of retinoids.

Animals↗
PubMed1991

Modulation of cellular cholesterol and its effect on cornified envelope formation in cultured human epidermal keratinocytes.

When cultured human epidermal keratinocytes (NHK) reach confluence they start to differentiate and an increase in the total cellular cholesterol content is observed. This increase parallels the appearance of a characteristic feature of terminal keratinocyte differentiation, the spontaneous formation of cornified envelopes (CE). Synthesis of CE is catalyzed by the plasma membrane-associated transglutaminase (TGm). Supplementation of the medium with inhibitors of cholesterologenesis suppressed increase in cholesterol levels and CE formation but did not interfere with TGm expression or TGm activity. Modulation of the plasma membrane cholesterol-phospholipid ratio of confluent NHK cultures using either pure phospholipid liposomes or liposomes enriched in cholesterol strongly affected spontaneous CE formation. Pure phospholipid liposomes completely inhibited CE formation, whereas cholesterol-enriched liposomes ensured envelope formation, even in the presence of inhibitors of cholesterol synthesis. From these results we conclude that in differentiating NHK an increase in the cellular cholesterol level is part of the differentiation program and is essential for the spontaneous CE formation.

Cell Aggregation↗
PubMed1991

Molecular anatomy of the neuro-immune connection.

Light microscopic immunohistochemistry was employed to elucidate and compare the presence, distribution, and coexistence of various peptides, neuroendocrine markers and enzymes of the catecholamine pathway in nerves supplying lymphoid tissues in a variety of mammalian species. All lymphoid organs and tissues receive innervation by fibers containing dopamine-beta-hydroxylase and/or tyrosine hydroxylase, neural markers like protein gene product 9.5, synaptophysin and neurofilament and a varied spectrum of peptides. The prominent peptides were tachykinins (substance P, neurokinin A), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), and vasoactive intestinal polypeptide/peptide histidine isoleucine (VIP/PHI). Opioid innervation was variable. Double immunofluorescence revealed coexistence of tachykinins and CGRP and of tyrosine hydroxylase and NPY. A minor proportion of fibers showed coexistence of NPY and tachykinins and of VIP/PHI and tachykinins. The possible importance of the complex peptidergic innervation of lymphoid tissues in inflammation, allergy, inflammatory pain and psycho-neuro-immuno-endocrine network function is discussed. A special immunomodulatory role of the sensory neurons is suggested.

Animals↗
PubMed1991

[Double-blind study of the comparative action of indomethacin 0.1% and placebo on the breakdown of the blood-retinal barrier].

The oral fluorophotometric exploration is able to simultaneously quantify the permeability of the blood aqueous (KIN, KOUT) and blood-retinal (PVPR) barriers. It is possible to detect the breakdown of the blood aqueous barrier 3 days after cataract surgery with this fluorophotometric method. Ocular inflammation is responsible for this leakage and non steroidal anti-inflammatory drugs prevent this breakdown. In this paper, we studied the effect of 0.1% indomethacin treatment to patients before and after cataract surgery. This double-blind study was performed in 34 patients: 18 patients in the indomethacin group and 16 patients in the placebo group. We showed that the apparent transfer coefficient of fluorescein in the anterior chamber (KIN) was statistically lower in the indomethacin group (0.0220 +/- 0.0179 hr-1) than in the placebo group (0.0371 +/- 0.0187 hr-1) on the 3rd postoperative day (p = 0.027).

Adult↗
PubMed1990

Cornified envelopes in congenital disorders of keratinization.

A morphological and biochemical analysis was made of cornified envelopes isolated from patients with different congenital disorders. Nomarski contrast microscopy of the envelopes showed that their morphology was not greatly altered in several types of keratoderma and parapsoriasis, but it was grossly modified in ichthyotic disorders. The various types of ichthyoses, keratoderma palmoplantare, KID syndrome and parapsoriasis showed, after cyanogen-bromide cleavage, peptide patterns similar to those obtained from healthy subjects. In contrast, envelopes from patients with Darier's disease, congenital pachyonychia and erythrokeratoderma variabilis showed markedly different peptide patterns.

Adolescent↗
PubMed1990

Reconstructed skin from cultured human keratinocytes and fibroblasts on a collagen-glycosaminoglycan biopolymer substrate.

A lattice prepared from biopolymer substrate bovine skin collagen and chondroitin-6-sulfate (glycosaminoglycan) served as a support for normal human keratinocytes and fibroblasts. Air exposure of the lattice on an agarose block gave rise to reconstructed epidermis, the histological features of which are very similar to normal human epidermis. Indirect immunofluorescence staining of the plasma membrane-associated transglutaminase, the enzyme responsible for the synthesis of the cornified envelope, revealed the same tissue distribution as observed in vivo. Cell cycle analysis showed a large shift of the normal human keratinocyte population into S-phase and cell division during the 1st week postinoculation. Furthermore, the effects of two modulators of differentiation (25-hydroxycholesterol and sodium butyrate) on the reconstruction of the epidermis were evaluated.

Animals↗
PubMed1989

Retinoic acid controls expression of epidermal transglutaminase at the pre-translational level.

Human epidermal keratinocytes were cultured until sub-confluence in low Ca2+ (0.15 mM) serum-free synthetic MCDB 153 medium. Raising the Ca2+ concentration to 1.15 mM caused an increase in envelope competence as well as plasma membrane associated transglutaminase (TGm) activity. This increase was not observed when the high Ca2+ medium contained retinoic acid. Immunofluorescence studies as well as immunoblotting with the TGm-specific monoclonal antibody B.C1 revealed that retinoic acid inhibits expression of TGm. Isolation and in vitro translation of mRNA with subsequent immunoprecipitation showed that retinoic acid inhibits TGm expression at the pretranslational level.

Antibodies, Monoclonal↗