Meeting Abstract
20.1 Monday, Jan. 4 Using trypsin digestion to determine the relative contributions of titin and collagen to passive elastic properties of whole muscles. POWERS, KL*; GILMORE, LA; MONROY, JA; UYENO, TA; NISHIKAWA, KC; Northern Arizona University Krysta.Powers@nau.edu
Several elastic proteins contribute to spring properties of resting muscle, including the giant titin protein, located within muscle sarcomeres, and collagen which constitutes the endomysium, perimysium, epimysium and tendinous attachments of muscle to bone. In this study, we investigated the relative contributions of collagen and titin to elastic recoil of passive muscle using trypsin digestion. Titin is particularly sensitive to digestion by trypsin. In a single muscle fiber or cardiac myocyte, nearly all titin is digested after incubation in trypsin for 30 min. In contrast, collagen is highly resistant to digestion by trypsin, and no measurable digestion of collagen can be detected after 16 hours of incubation with trypsin. After incubating a whole soleus muscle in trypsin for 16 hr, only a collagen ghost remains, allowing quantification of the contribution of collagen to muscle elastic properties. To test for a contribution of titin to passive elastic recoil, whole soleus muscles from mouse were incubated in trypsin for 1 hr or 16 hr prior to stretch and/or passive load clamp tests. We compared the elastic properties of individual soleus muscles during passive stretch and passive elastic recoil in load clamp tests before trypsin digestion, after 1 hour of trypsin digestion, and after 16 hours of trypsin digestion. Preliminary data suggest that titin contributes significantly to passive tension of whole soleus muscles, and that the contribution of titin to passive stretch is greatest at resting length, and declines relative to the contribution of collagen with increasing stretch. These data will be used to estimate parameters for a constitutive model of mouse soleus muscle that can be used to predict the contributions of these elastic proteins to active as well as passive stretch and recoil.
