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  • 1
    Electronic Resource
    Electronic Resource
    2,4-dinitrophenol, lysosomal breakdown and rapid myofilament degradation in vertebrate skeletal muscle (1980)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 315 (1980), S. 77-82 
    Details
    ISSN: 1432-1912
    Keywords: Muscle ; Lysosomes ; Calcium ; Muscular dystrophy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. The possibility that rapid Ca2+-uptake by skeletal muscle mitochondria may cause local reductions in pH i (by H+/Ca2+ exchange) and so promote lysosomal breakdown has been explored using amphibian and mammalian preparations. Recent studies suggested that such a sequence of events is possible in cardiac muscle. 2. However, extensive muscle damage can still be initiated in skeletal muscle when the mitochondria are uncoupled so that Ca2+-uptake is prevented. 3. DNP alone induces extensive myofilament degradation which is similar to that produced by A 23187 and caffeine and described previously. 4. It is suggested that (a) the known action of DNP in promoting lysosomal labilization in living cells is produced by mitochondrial uncoupling and the release of stored Ca2+, (b) raised [Ca2+] i promotes lysosomal breakdown in skeletal muscle, so that the hydrolases released effect myofilament dissolution rapidly. 5. DNP also rapidly causes septation and division of the mitochondria in mammalian skeletal muscle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00504233
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  • 2
    Electronic Resource
    Electronic Resource
    The action of caffeine in promoting ultrastructural damage in frog skeletal muscle fibres (1978)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 305 (1978), S. 159-166 
    Details
    ISSN: 1432-1912
    Keywords: Caffeine ; Muscle ; Muscular dystrophy ; Calcium ; A23187
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Caffeine at concentrations above 5 mM was shown to cause rapidly extensive ultrastructural damage to the myofibrils of frog skeletal muscle. 2. The effect was promoted at lower temperatures, whereas the myofibrils were protected by prior exposure to procaine. 3. It is argued that caffeine causes a Ca2+-induced release of Ca2+ (the CROC) from the S.R. and that the consequent rise in [Ca2+]i promotes the ultrastructural damage observed. 4. Myofibril degradation is also produced by treatment of the muscle with the divalent cation ionophore A23187; this effect is not protected by either procaine or Dantrolene sodium. 5. It is suggested that A23187 causes the release of Ca2+ from the S.R. by a mechanism that differs from both excitation and the CROC; the resultant rise in [Ca2+]i again causes myofibril degradation. 6. The ways in which a marked rise in [Ca2+]i could cause muscle damage and the possible relevance of these findings to the sequence of events in the development of myopathies of human skeletal muscle are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00508287
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  • 3
    Electronic Resource
    Electronic Resource
    Stimulation of the frequency of MEPPs at the frog neuromuscular junction by extracellular EGTA (1980)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 315 (1980), S. 29-35 
    Details
    ISSN: 1432-1912
    Keywords: Calcium ; Neuromuscular junction ; Spontaneous release ; MEPP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Exposure of the frog neuromuscular junction at 17° C or 23° C to salines with low [Ca2+], buffered with EGTA, causes mepp frequency to fall after 4–6 min to about 20% of the control rate. Results obtained in the presence of verapamil suggest that this fall is a consequence of a lower Ca2+-influx coupled with the action of the extracellular EGTA in promoting Ca2+-efflux from the terminals. These findings confirm the suggestion that [Ca2+]i has a major role in determining mepp frequency. At 13° C, the fall in mepp frequency after addition of EGTA is preceded by a transient (1–2 min) rise in mepp rate which is not present at 17° C or in the presence of verapamil. This transient acceleration in spontaneous release is believed to be because EGTA promotes the emptying of a Ca2+-reservoir on or beneath the inner face of the membrane, thus causing a rapid Ca2+-efflux via the Ca2+-sensitive sites that trigger exocytosis of transmitter. The significance of the sensitivity of the response to temperature is discussed. The suppressive effect of higher temperatures can be reversed to some extent by hyperosmotic salines, an effect that may reflect the action of hypertonicity on the plasmalemma. It is concluded that the characteristics of the release system may change markedly at about 16° C. Ca2+-EGTA buffers are widely used; it is suggested that extracellular EGTA can also modify [Ca2+]i in cellular systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00504227
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of the ionophore A23187 on the ultrastructure and electrophysiological properties of frog skeletal muscle (1976)
    Springer
    Cell & tissue research 173 (1976), S. 193-209 
    Details
    ISSN: 1432-0878
    Keywords: Muscle ; Ionophore A23187 ; Calcium ; Muscular dystrophy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The divalent cation ionophore A23187 has three major effects on the thin cutaneous pectoris muscle of frog: (1) The membrane potential is depolarized, an action that is found only when the [Ca2+] of the bathing saline is very low. (2) It causes an increase in resting tension and the development of contraction. This action is produced at both normal and low values of [Ca2+]o and is, therefore, independent of Ca2+ entry and of changes in Em. The ionophore is believed to act primarily by releasing Ca2+ from intracellular stores. (3) It causes major ultrastructural damage to the muscle filaments. It is believed that this damage is the result of the action of A23187 on the sarcoplasmic reticulum and the elevation of [Ca2+]i and we suggest that the action of this ionophore may serve as a useful model for the study of certain myopathies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00221375
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  • 5
    Electronic Resource
    Electronic Resource
    Are lysosomal enzymes involved in rapid damage in vertebrate muscle cells? (1988)
    Springer
    Cell & tissue research 253 (1988), S. 447-455 
    Details
    ISSN: 1432-0878
    Keywords: Lysosomes ; Muscle damage ; Calcium ; Lysosomotropic agents ; Phospholipase A2 ; Frog (Rana temporaria) ; Guinea pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Experiments with lysosomotropic agents suggest that the sarcotubular system subserves some of the functions of the lysosomal apparatus in frog skeletal muscle. Dinitrophenol or A23187 trigger lysosome labilization and myofilament damage in mammalian cardiac muscle. Lysolecithin labilizes isolated liver lysosomes, but has no action following phospholipase A2 activation in vivo. Zinc ions or a pHi of 7.5 do not protect against myofilament damage. In fractions from mammalian cardiac muscle, calcium and calmodulin do not cause lysosomal labilization whereas cGMP does but only at high concentration (10-4 M). It is concluded that lysosomal hydrolases play no significant part in rapid muscle damage. It is suggested that rises in [Ca]i activate two separate pathways causing (i) myofilament damage; (ii) sarcolemmal (and possibly lysosomal) membrane damage via phospholipase A2 and lipoxygenase activity. Dinitrophenol triggers both pathways independently and thus may cause lysosome labilization. The possibility that the sarcoplasmic reticulum is the site generating myofilament damage is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00222302
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  • 6
    Electronic Resource
    Electronic Resource
    The role of phospholipase A2 in calcium-induced damage in cardiac and skeletal muscle (1988)
    Springer
    Cell & tissue research 253 (1988), S. 457-462 
    Details
    ISSN: 1432-0878
    Keywords: Muscle damage ; Cardiac muscle ; Calcium ; Phospholipase A2 ; Lipoxygenase ; Cyclo-oxygenase ; Rana ttemporaria ; Mouse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary This study compares the action of inhibitors of the eicosanoid cascade on calcium-induced myofilament damage in cardiac muscle of the perfused frog heart and incubated frog ventricle slices, and in skeletal muscle of incubated mammalian diaphragm and isolated and saponin-skinned amphibian pectoris cutaneous muscle. Mepacrine (10-5M) and indomethacin (3×10-6M) protected completely against myofilament damage induced by entry of calcium in the ‘calcium-paradox’ in frog heart. However, inhibition of phospholipase A2 (PLA2) (with chlorpromazine, 2×10-4M, or mepacrine, 10-5M, 5x10-5M), of cyclo-oxygenase enzymes (with indomethacin, 3x10-6M to 10-5M or BW755C, 3.8x10-4M), or of lipoxygenase enzymes (with BW755C, 3.8x10-4M or nordihydroguaiaretic acid, 2x10-6M or 5x10-6M) all failed in intact cardiac or skeletal muscle cells to prevent the myofilament damage that is rapidly triggered by 10-2M caffeine, 6x10-6M ruthenium red, 10-4M DNP or 5 μg ml-1 A23187. These agents also failed completely to protect against myofilament damage in saponin-skinned amphibian skeletal muscle when [Ca]i was raised to 8x10-6M. Thus, inhibition of PLA2 does not protect the myofilament apparatus against calcium released intracellularly, and it is suggested that mepacrine and indomethacin can block entry of calcium in the calcium-paradox in the amphibian heart. Chlorpromazine (2x10-4M) and mepacrine (10-3M) at zero [Ca] caused severe myofilament damage in skinned muscle, possibly due to an effect on membranes. Since inhibitors of PLA2 and of lipoxygenases prevent efflux of creatine kinase and sarcolemma damage in mammalian skeletal muscle, it is evident that experimentally-induced rises in [Ca]i (by caffeine or A23187) can trigger two separate pathways: (i) PLA2 and the arachidonic acid cascade which culminate in membrane damage, and (ii) a different, Ca-activated system that causes rapid damage of myofilaments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00222303
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