Whole-cell lysates were isolated from the homogenized skeletal muscle samples with a ristocetin-induced platelet agglutination buffer (Boston Bioproducts, Worcester, Massachusetts) and centrifuged at 12 000g for 10 minutes at 4°C to separate soluble fractions from insoluble fractions. Protein concentration was measured spectrophotometrically at a 595-nm wavelength with a DC protein assay kit (Bio-Rad Laboratories, Inc, Hercules, California). Forty to eighty micrograms of total protein was fractionated by a 4% to 20% gradient in sodium dodecyl sulfate–polyacrylamide gel electrophoresis (Invitrogen, San Diego, California) and transferred to polyvinylidene difluoride membranes (Millipore, Bedford, Massachusetts). Each membrane was incubated with specific antibodies as follows: antiplasminogen antibody (dilution, 1:500) (Calbiochem, San Diego, California), antiangiostatin antibody (dilution, 1:2500) (BD Biosciences, San Jose, California), anti–collagen XVIII antibody (dilution, 1:300) (Santa Cruz Biotech, Santa Cruz, California), antiendostatin antibody (dilution, 1:1000) (Upstate, Chicago, Illinois), anti–MMP-2 antibody (dilution, 1:500) (Calbiochem), anti–MMP-9 antibody (dilution, 1:500) (Millipore), and anti–tissue inhibitor of metalloproteinase 2 (TIMP-2) antibody (dilution, 1:300) (Calbiochem). The membranes were subsequently incubated for 1 hour in diluted appropriate secondary antibody (Jackson Immunolab, West Grove, Pennsylvania). Immune complexes were visualized with the enhanced chemiluminescence detection system (Amersham, Piscataway, New Jersey). Bands were quantified by densitometry of radioautograph films. Ponceau S staining was performed to confirm equivalent protein loading.