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MUSCLE CELL BIOLOGY AND CELL MOTILITY

Force transmission, compliance, and viscoelasticity are altered in the ₇-integrin-null mouse diaphragm

¹Department of Medicine, Baylor College of Medicine, Houston, Texas; and ²Wellcome Trust Center for Cell-Matrix Research, Manchester, United Kingdom

Submitted 26 August 2003 ; accepted in final form 20 August 2004

₇₁ integrin is a transmembrane structural and receptor protein of skeletal muscles, and the absence of ₇-integrin causes muscular dystrophy. We hypothesized that the absence of ₇-integrin alters compliance and viscoelasticity and disrupts the mechanical coupling between passive transverse and axial contractile elements in the diaphragm. In vivo the diaphragm is loaded with pressure, and therefore axial and transverse length-tension relationships are important in assessing its function. We determined diaphragm passive length-tension relationships and the viscoelastic properties of its muscle in 1-month-old ₇-integrin-null mice and age-matched controls. Furthermore, we measured the isometric contractile properties of the diaphragm from mutant and normal mice in the absence and presence of passive force applied in the transverse direction to fibers in 1-month-old and 5-month-old mutant mice. We found that compared with controls, the diaphragm direction of ₇-integrin-null mutants showed 1) a significant decrease in muscle extensibility in 1-year-old mice, whereas muscle extensibility increased in the 1-month-old mice; 2) altered muscle viscoelasticity in the transverse direction of the muscle fibers of 1-month-old mice; 3) a significant increase in force-generating capacity in the diaphragms of 1-month-old mice, whereas in 5-month-old mice muscle contractility was depressed; and 4) significant reductions in mechanical coupling between longitudinal and transverse properties of the muscle fibers of 1-month-old mice. These findings suggest that ₇-integrin serves an important mechanical function in the diaphragm by contributing to passive compliance, viscoelasticity, and modulation of its muscle contractile properties.

muscular dystrophy; respiratory muscles; transmembrane proteins

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