calcimycin and Muscular-Diseases

It is suggested that various muscle diseases and examples of experimentally-induced muscle damage arise because of a high calcium level in the myoplasm. When [Ca2+]i is raised experimentally in amphibian or mammaliam muscle by treatment with A23187 or caffeine, myofilament degradation follows quickly. Such a rapid action suggests the involvement of a sequence of proteolytic activity that is stimulated by a rise in [Ca2+]i. Ca2+ might either trigger protease activity directly or indirectly, or promote the release of lysosomal enzymes. A high [Ca2+]i in dystrophic muscle is believed to be the resultant of a sequence of events that is summarized in the figure. Suggestions are presented for different ways in which the steady-state position of [Ca2+]i might ultimately be controlled for the clinical amelioration of some dystrophic conditions.

Topics: Animals; Caffeine; Calcimycin; Calcium; Cell Membrane; Humans; Magnesium; Muscular Diseases; Muscular Dystrophies; Nucleotides, Cyclic; Osmolar Concentration; Peptide Hydrolases; Sarcoplasmic Reticulum

The role of Ca(2+)-dependent phospholipase A2 (PLA2) in the mechanism of skeletal muscle damage in broiler chickens was examined in vitro using a novel, synthetic, PLA2-specific inhibitor Ro31-499/001 (Ro31). Muscle damage was assessed by measurement of creatine kinase (CK) efflux from isolated muscles into the incubation medium. Treatment with the specific Ca(2+)-ionophore 4-Br-A23187 (5 microM) caused a 72% elevation (P<0.05) in muscle 45Ca2+ accumulation, which was associated with a marked increase (P<0.001) in muscle CK efflux (7.6-fold). Incubation with Ro31 (50 microM) reduced (P<0.001) CK efflux from muscles treated with ionophore (45%) but was without effect on 45Ca accumulation. Treatment with the Na+ ionophore monensin (100 microM) induced 55% (P< 0.05) elevation in 45Ca2+ accumulation with a concomitant 2.5-fold increase (P<0.001) in CK loss. Muscles incubated with monensin in the presence of Ro31 exhibited a 49% reduction (P<0.001) in CK leakage but showed no change in 45Ca2+ uptake. The results indicate that increasing external Ca2+ entry, directly or indirectly, and elevation of intracellular Ca2+, significantly alters sarcolemmal integrity resulting in increased CK efflux from broiler skeletal muscle. This process is, at least in part, dependent upon activation of PLA2 activity and thus inhibitable by Ro31. It is further proposed that muscle damage in poultry induced by a range of stresses, and insults may also be mediated by a Ro31 sensitive, PLA2-dependent component. The findings have implications for strategies to reduce or prevent myopathies in poultry affecting bird welfare and product quality.

Topics: Animals; Calcimycin; Calcium; Chickens; Creatine Kinase; Enzyme Activation; Enzyme Inhibitors; Female; Ionophores; Muscle, Skeletal; Muscular Diseases; Phospholipases A; Phospholipases A2; Poultry Diseases

1. Incubation of rat diaphragm muscles in the presence of Ca(2+)-ionophore A23187, which causes accumulation of free intracellular Ca2+, induced severe myofibrils damage. Electron microscopic studies have revealed that calmodulin (CaM) antagonists, trifluoperazine, thioridazine, pimozide and CGS 9343B, were most effective in preserving muscle structure. 2. The CaM antagonists raised the decreased glucose-1,6-bisphosphate levels, induced by high Ca2+, with a concomitant activation of the reduced cytosolic phosphofructokinase (the rate limiting enzyme of glycolysis) and thereby cytosolic glycolysis. 3. All four CaM inhibitors also prevented solubilization of cytoskeleton-bound glycolytic enzymes by high Ca2+. 4. The protective effect of these compounds on cytosolic and cytoskeletal glycolysis, was also expressed by their action in preserving muscle ATP levels. 5. The present experiments suggest that CaM antagonists may be effective drugs in treatment of muscle damage and various muscle diseases, which are characterized by a high pathological increase in intracellular Ca2+.

Topics: Adenosine Triphosphate; Animals; Calcimycin; Calcium; Calmodulin; Cytosol; Glucose-6-Phosphate; Glucosephosphates; In Vitro Techniques; Microscopy, Electron; Muscular Diseases; Myofibrils; Phosphofructokinase-1; Rats; Respiratory Muscles

The role of arachidonic acid metabolism in the efflux of intracellular enzymes from damaged skeletal muscle has been examined in vitro using inhibitors of cyclo-oxygenase and lipoxygenase enzymes. Damage to skeletal muscle induced by either calcium ionophore A23187 (25 microM) or dinitrophenol (1 mM) caused an increase in the efflux of prostaglandins E2 and F2 alpha together with a large efflux of intracellular creatine kinase. Use of a cyclo-oxygenase inhibitor completely prevented the efflux of prostaglandins, but had no effect on creatine kinase efflux. However, several agents having the ability to inhibit lipoxygenase enzymes dramatically reduced creatine kinase efflux following damage. These data suggest that a product or products of lipoxygenase enzymes may be mediators of the changes in plasma membrane integrity which permit efflux of intracellular enzymes as a consequence of skeletal muscle damage.

Topics: 2,4-Dinitrophenol; 4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyrazol-3-amine; Animals; Arachidonate Lipoxygenases; Arachidonic Acid; Arachidonic Acids; Calcimycin; Creatine Kinase; Cyclooxygenase Inhibitors; Dinitrophenols; Female; In Vitro Techniques; Masoprocol; Muscles; Muscular Diseases; Phenylacetates; Prostaglandins; Pyrazoles; Rats; Rats, Inbred Strains

[Ca2+]i was raised experimentally in mammalian and amphibian skeletal and cardiac muscles by A23187, DNP, anoxia or the Ca2+ -paradox. Trifluoperazine (TFP) at 10(-5) M failed to protect against the characteristic and rapid damage triggered by elevated [Ca2+]i in any of the preparations. It is concluded that calmodulin is not implicated in this rapid ultrastructural damage. TFP alone also causes identical patterns of damage. It may be acting to raise [Ca2+]i in skeletal and cardiac muscle cells.

Topics: Animals; Calcimycin; Calcium; Coronary Disease; Dinitrophenols; Hypoxia; Mice; Muscular Diseases; Rana temporaria; Subcellular Fractions; Trifluoperazine

We evaluated the possible role of prostaglandin E2 (PGE2) in the calcium(Ca++)-mediated damage of skeletal muscle by a calcium ionophore (A23187) that induces excessive Ca++ influx. Twitch and tetanus of rat diaphragms were depressed with either PGE2 or A23187. A23187-induced depression was reduced by PG synthesis inhibitors, aspirin, or indomethacin, though less than that by a protease inhibitor, leupeptin. PGE2-induced depression was also inhibited by leupeptin. Damage of the muscle cell by excessive intracellular free Ca++ may thus be mediated via a PGE2 pathway besides other mechanisms including non-lysosomal, Ca++-activated proteases.

Topics: Animals; Calcimycin; Male; Muscle Contraction; Muscular Diseases; Prostaglandins E; Rats

Electron micrographs show that treatment of mouse diaphragm with the divalent cation ionophore A23187 causes major ultrastructural damage in the muscle. During the first 30 min of exposure to A23187, the mitochondria swell markedly but after 40 min they undergo further ultrastructural changes and a rapid dissolution of the myofilaments is also seen at this time. In place only remnants of the filaments remain. It is suggested that the ionophore causes the release of Ca2+ from the sarcoplasmic reticulum which, initially, is taken up by the mitochondria, causing then to swell; after 40 min the mitochondria release the accumulated Ca2+. It is argued that the rise in [ca2+]i stimulates neutral proteases in the myoplasm and that the sequence of events following ionophore treatment may act as a model for the involvement of Ca2+ in various myopathies. We have shown previously (29) that treatment of the cutaneous pectoris muscle of the frog with the divalent cation ionophore A23187 has three major effects: (i) The membrane potential (Em) is depolarized, an action that is found only when the Ca2+ -concentration of the bathing saline is very low. (ii) It causes an increase in resting tension and the development of contraction. This effect is found at both normal (1.8 mM) 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. (iii) It causes major ultrastructural damage to the muscle filaments. The evidence suggests that A23187 acts at the sarcoplasmic reticulum of frog muscle, causing the release of stored Ca2+ , and the consequent rise in [Ca2+]i stimulates a Ca2+ -activated protease which is responsible for the myofilament degradation. A calcium-activated factor has been isolated from rabbit skeletal muscle; this enzyme operates at neutral pH, hydrolyses denatured casein, and specifically removes the Z-lines and alpha-actinin from skeletal muscle (24). A Ca2+ -activated protease with a pH optimum of 7.5 has also been purified from porcine skeletal muscle; it removes Z-discs, degrades troponin and tropomyosin and partly degrades M lines, and it has been suggested that it may have a physiological role in the disassembly of intact myofibrils during the metabolic turnover of myofibrillar proteins (6, 7). This protases is not localized in membrane-bounded sub-cellular particles, but is believed to be in direct contact with the cytoplasm (26). Th

Topics: Animals; Anti-Bacterial Agents; Calcimycin; Calcium; Mice; Microscopy, Electron; Mitochondria, Muscle; Muscles; Muscular Diseases; Myofibrils; Organoids; Sarcoplasmic Reticulum; Time Factors