melitten and Muscular-Dystrophy--Animal

Duchenne muscular dystrophy is caused by deficiency of dystrophin and leads to progressive weakness. It has been proposed that the muscle degeneration occurring in this disease is caused by increased Ca2+ influx due to enhanced activity of cationic channels that are activated either by stretch of the plasma membrane (stretch-activated channels) or by Ca2+-store depletion (store-operated channels). Using both cytosolic Ca2+ measurements with Fura-2 and the manganese quench method, we show here that store-operated Ca2+ entry is greatly enhanced in dystrophic skeletal flexor digitorum brevis fibers isolated from mdx(5cv) mice, a mouse model of Duchenne muscular dystrophy. Moreover, we show for the first time that store-operated Ca2+ entry in these fibers is under the control of the Ca2+-independent phospholipase A2 and that the exaggerated Ca2+ influx can be completely attenuated by inhibitors of this enzyme. Enhanced store-operated Ca2+ entry in dystrophic fibers is likely to be due to a near twofold overexpression of Ca2+-independent phospholipase A2. The Ca2+-independent phospholipase A2 pathway therefore appears as an attractive target to reduce excessive Ca2+ influx and subsequent degeneration occurring in dystrophic fibers.

Topics: Anilides; Animals; Caffeine; Calcium Channels; Calcium Signaling; Group VI Phospholipases A2; Ion Transport; Manganese; Melitten; Mice; Mice, Inbred C57BL; Mice, Inbred mdx; Models, Biological; Muscle Fibers, Skeletal; Muscle, Skeletal; Muscular Dystrophy, Animal; Naphthalenes; Phospholipases A; Phospholipases A2; Potassium Chloride; Pyrones; Sarcoplasmic Reticulum Calcium-Transporting ATPases; Thiadiazoles

Focal lesions in the plasma membrane overlying wedge-shaped defects in muscle fibers ("delta lesions") are an early pathological change in Duchenne muscular dystrophy (DMD). Abnormalities in the plasma membrane have been suggested as a cause of these lesions and of the degeneration of muscle fibers in DMD. We investigated the role of plasma membrane defects in the production of delta lesions by examining the effects of a series of membrane-active agents--lysolecithin, deoxycholate, Triton X-100, and melittin--on the muscles of rats in vivo. Within minutes after treatment with these agents, the muscle fibers developed typical delta lesions. Identical morphological changes were produced by the calcium ionophore A23187, suggesting that calcium entry may play an important role in this process. We conclude that damage to the plasma membrane or calcium entry can reproduce characteristic features of the muscle pathology seen in DMD. This model should prove useful in elucidating the mechanisms of muscle fiber damage and degeneration in DMD.

Topics: Animals; Cell Membrane; Deoxycholic Acid; Female; Lysophosphatidylcholines; Melitten; Muscles; Muscular Dystrophy, Animal; Rats; Rats, Inbred Strains