title: The role of proteases in excitation-contraction coupling failure in muscular dystrophy.
abstract: Duchenne muscular dystrophy (DMD) is one of the most frequent types of muscular dystrophy. Alterations in intracellular calcium (Ca(2+)) handling are thought to contribute to the disease severity in DMD, possibly due to the activation of Ca(2+)-activated proteases. The purpose of this study was twofold: 1) to determine whether prolonged excitation-contraction (E-C) coupling disruption following repeated contractions is greater in animals lacking both dystrophin and utrophin (mdx/Utr(-/-)) compared with mice lacking only dystrophin (mdx); and 2) to assess whether protease inhibition can prevent E-C coupling failure following repeated tetani in these dystrophic mouse models. Excitation-contraction coupling was assessed using Fura-2 ratio, as an index of intracellular free Ca(2+) concentration, in response to electrical stimulation of single muscle fibers from the flexor digitorum brevis muscle. Resting Fura-2 ratio was higher in dystrophic compared with control (Con) fibers, but peak Fura-2 ratios during stimulation were similar in dystrophic and Con fibers. One hour after a series of repeated tetani, peak Fura-2 ratios were reduced by 30 ± 5.6%, 23 ± 2%, and 36 ± 3.1% in mdx, mdx/Utr(+/-), and mdx/Utr(-/-), respectively, with the greatest reduction in mdx/Utr(-/-) fibers (P < 0.05). Protease inhibition attenuated this decrease in peak Fura-2 ratio. These data indicate that E-C coupling impairment after repeated contractions is greatest in fibers lacking both dystrophin and utrophin and that prevention of protease activation can mitigate the prolonged E-C coupling impairment. These data further suggest that acute protease inhibition may be useful in reducing muscle weakness in DMD.
authors.affiliation: Department of Kinesiology, School of Public Health, University of Maryland, College Park, Maryland; and.
authors.forename: Davi A G
authors.initials: DA
authors.lastname: Mázala
authors.affiliation: Department of Human Nutrition, Foods and Exercise, Virginia Polytechnic Institute and State University, Blacksburg, Virginia.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Grange
authors.affiliation: Department of Kinesiology, School of Public Health, University of Maryland, College Park, Maryland; and erchin@umd.edu.
authors.forename: Eva R
authors.initials: ER
authors.lastname: Chin
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004195:Disease Models, Animal; D004558:Electric Stimulation; D056966:Excitation Contraction Coupling / Q000187:drug effects; D018101:Mice, Inbred mdx; D018345:Mice, Knockout; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000201:enzymology*; D053580:Muscle Strength; D018908:Muscle Weakness; D018482:Muscle, Skeletal / Q000187:drug effects / Q000201:enzymology* / Q000503:physiopathology; D020388:Muscular Dystrophy, Duchenne / Q000188:drug therapy / Q000201:enzymology* / Q000235:genetics / Q000503:physiopathology; D010447:Peptide Hydrolases / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D013997:Time Factors; D049411:Utrophin / Q000172:deficiency / Q000235:genetics
chemical_list: D011480:Protease Inhibitors; D049411:Utrophin; D010447:Peptide Hydrolases; D002118:Calcium
keywords: Duchenne muscular dystrophy; excitation-contraction coupling; intracellular Ca2+; protease(s)