Meeting Abstract

28.3  Wednesday, Jan. 5  The Relative Contributions of Titin and Collagen to Passive Tension POWERS, KL*; MONROY, JA; GILMORE, LA; NISHIKAWA, KC; Northern Arizona University krysta.powers@nau.edu

Passive tension in an intact muscle has been attributed primarily to titin and collagen. This study aims to quantify the relative contributions of titin and collagen to passive tension in the intact mouse soleus muscle. Trypsin readily digests titin but has negligible effects on collagen, making this enzyme ideal for quantification of the contributions of these proteins to muscle elasticity. We used mice with the muscular dystrophy with myositis (mdm) mutation, resulting in a ~779 bp deletion in the N2A region of titin. Passive tension was measured at 30 minutes and 16 hours after trypsin digestion and compared among heterozygous, wild-type, and homozygous mutant B6C3Fe-a/a-mdm mice. Mdm genotypes differ in passive elasticity of the soleus muscle. Passive tension is greater in mdm mice than in wild-type mice, and intermediate in heterozygotes. After 30 minutes trypsin digestion, passive tension decreased substantially in all genotypes by an average of 73% (p =0.19), suggesting that titin is a major contributor to passive tension in the intact mouse soleus. After 16 hours trypsin digestion, all proteins except collagen are degraded, leaving a collagen ghost. In all genotypes, collagen contributed an average of 11% to passive tension (p=0.77). There was no difference in collagen or titin contribution across genotypes. This study suggests that titin is the major contributor to passive tension in the intact mouse soleus muscle, and differences in gait and passive elastic properties among genotypes are not due to variations in collagen. Research supported by NSF IOS-0732949, II5-0827688, IOS-1025806.