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  • 1
    Electronic Resource
    Electronic Resource
    Low concentrations of formaldehyde induce DNA damage and delay DNA repair after UV irradiation in human skin cells (2004)
    Oxford, UK; Malden, USA : Munksgaard International Publishers
    Experimental dermatology 13 (2004), S. 0 
    Details
    ISSN: 1600-0625
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract:  Long-term occupational exposure to formaldehyde (FA) increases the risk for nasopharyngeal squamous cell carcinoma. As the skin is also in contact with FA by environmental exposure, we tested the genotoxic properties of appropriate low concentrations (〈100 µM) of FA on cultured keratinocytes and fibroblasts of human skin. The initial DNA damage was assessed by comet assay. The induction of DNA protein crosslinks was measured by the ability of FA to reduce DNA migration induced by methyl-methane-sulfonate. Upon 4 h of exposure to FA, significant (P 〈 0.05) crosslink formations were observed in fibroblasts (50 µM FA) and in keratinocytes (25 µM FA). Upon 8 h of exposure to FA (25 µM FA), significant crosslink formations were observed in both the cell types. FA is known to inhibit different DNA repair pathways. Therefore, we studied the effect of FA on UV-induced repair. Human keratinocytes and fibroblasts exposed to 10 µM FA prior to UV irradiation showed disturbed repair kinetics after UVC and UVB, but not after UVA irradiation. Single-strand breaks (SSBs) derived from nucleotide excision repair disappeared 6 h after solely UVC (3 mJ/cm2) or 3 h solely UVB (30 mJ/cm2) exposure in both the cell types. In the presence of FA, SSBs were still present at these time points containing a reference to a delay in DNA resynthesis/ligation. FA at a concentration not inducing micronuclei (12.5 µM) caused significant increase of UVC-induced (4 mJ/cm2) chromosomal damage. Proliferation of keratinocytes and fibroblasts was in parallel to observed DNA damages. In conclusion, our data suggest that environmental exposure to FA may contribute to UV-induced skin carcinogenesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0906-6705.2004.00157.x
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  • 2
    Electronic Resource
    Electronic Resource
    Proliferative Merkel cells were not detected in human skin (1996)
    Springer
    Archives of dermatological research 288 (1996), S. 184-187 
    Details
    ISSN: 1432-069X
    Keywords: Key words Merkel cells ; Cytokeratins ; Cell proliferation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The fetal development of Merkel cells – neuroendocrine cells of the skin – has been a matter of debate for a long time. Recent results have helped to confirm their intraepidermal development in humans. Simple epithelial cytokeratins (CK) nos. 8, 18, 19 and 20 are well established markers at the light microscopic level. These cells could be detected from fetal week 8 within the epidermis with an enormous increase during the following weeks. This gives rise to the question as to whether Merkel cells are undergoing mitoses or whether they are derived from basal keratinocytes. We studied fetal and adult skin using antibodies to simple epithelial CK and to Ki67, a human nuclear cell proliferation-associated antigen in an attempt to answer these questions. In human adult and fetal skin of various stages we could not detect any Merkel cells undergoing cell division. These results suggest that Merkel cells are postmitotic cells to be renewed from undifferentiated keratinocytes with stem cell characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004030050044
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  • 3
    Electronic Resource
    Electronic Resource
    Magnesium und die Hemmung der Actin-Myosin-Interaktion in isolierten contractilen Strukturen der fibrillären Insektenmuskeln (1969)
    Springer
    Pflügers Archiv 311 (1969), S. 256-264 
    Details
    ISSN: 1432-2013
    Keywords: Flight Muscle ; Ca2+−Mg2+-Dependence ; Stretchactivation of ATPase ; Oscillation ; Actin-Myosin-Interaction-Inhibition ; Insekten-Flugmuskeln ; Ca2+−Mg2+-Einfluß ; Dehnungsaktivierung der ATPase ; Oscillation ; Actin-Myosin-Interaktionsinhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Die Wirkung von verschiedenen Inhibitoren der Actin-Myosin-Interaktion (EGTA1, PES, Harnstoff, Thioharnstoff, Äthylakohol und Mg-Ionen) wurde untersucht, um zu prüfen, ob die Dehnungsaktivierung und Oscillationsfähigkeit von wasserglycerinextrahierten, asynchronen Flugmuskeln (DLM) der tropischen Wasserwanze (Lethocerus maximus) an die Actin-Myosin-Interaktion gebunden ist. Die chemisch heterogenen Interaktionshemmer wirken im Gegensatz zu früheren Befunden nicht einheitlich. EGTA und PES reaktivieren den strukturgebundenen Kontraktionshemmer (Troponin), indem sie die freien Ca-Ionen binden. Thioharnstoff, Harnstoff und Äthylalkohol sind von Ca-Ionen unabhängig und umgehen in ihrr Wirkung den Ebashi-Faktor. Freies Magnesium oder Mg-ATP ist ein für den contractilen Mechanismus der fibrillären Insektenmuskeln spezifischer Interaktionsinhibitor, der für die Dehnungsaktivierung und Oscillation der Fasern in einer optimalen (partielle Hemmung hervorrufenden) Konzentration vorhanden sein muß. Mg2+ hemmen die Spannungsentwicklung, ATPase und die Verkürzung extrahierter Insektenflugmuskeln. Die Fasern können nur dann oscillieren, wenn sie sich in einem Zustand der mittleren Aktivierung und mittleren Hemmung befinden, aus welchem sie durch Dehnung aktiviert und durch Entdehnung deaktiviert werden können.
    Notes: Summary The effect of different inhibitors of the actin-myosin interaction (EGTA, PES, urea, thiourea, ethanol and magnesium-ions) was studied to find out whether the stretch-activation and the ability of oscillation of glycerol-extracted, fibrillar dorsal-longitudinal flight muscle of the tropical water bug Lethocerus is based on the actin-myosin-interaction. In contrast to previous findings these chemically heterogeneous inhibitors do not react according to an uniform mechanism. EGTA and PES reactivate a structure bound contraction inhibitor (troponin) by complexing with the free Ca2+. Thiourea, urea and ethanol act independantly of Ca2+; they by-pass troponin. Free magnesium or Mg-ATP is an interaction inhibitor specific for the contractile mechanisms of the fibrillar insect muscle. Mg2+ partly inhibits the development of tension, ATPase-activity and shortening of extracted insect flight muscle. For oscillation it has to be present in an optimal concentration in order to maintain a state of medium activity from which the muscle can be further activated by stretch or deactivated by release.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00590529
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