INCREASED COMPLIANCE IN DIAPHRAGM MUSCLE OF THE CARDIOMYOPATHIC SYRIAN-HAMSTER

We investigated the hypothesis that diaphragm compliance was abnormal in cardiomyopathic Syrian hamsters (CSH), an experimental model of myo pathy. The passive elastic properties of isolated diaphragm muscles we re analyzed at both the muscle and sarcomere levels. We used the follo wing passive exponential relationship between stress (sigma) and strai n (epsilon): sigma = (E-o/beta) (e(beta epsilon) - 1), where E-o is th e initial elastic modulus and beta is the stiffness constant. Immunocy tochemistry procedures were used to analyze the distribution of two ke y elastic components of muscle, extracellular collagen and intracellul ar titin elastic components, as well as the extracellular matrix glyco protein laminin. Muscle and sarcomere values of beta were nearly twofo ld lower in CSH (8.7 +/- 1.9 and 8.3 +/- 1.4, respectively) than in co ntrol animals (19.7 +/- 1.7 and 16.8 +/- 2.1, respectively) (P < 0.01 for each). Compared with controls, E-o was higher in CSH. Sarcomere sl ack length was significantly longer in CSH than in control animals (2. 1 +/- 0.1 vs. 1.9 +/- 0.1 mu m, P < 0.05). The surface area of collage n I was significantly larger in CSH (17.4 +/- 1.8%) than in control an imals (12.4 +/- 0.7%, P < 0.05). There was no change in the distributi on of titin or laminin labelings between the groups. These results dem onstrate increased diaphragm compliance in cardiomyopathic hamsters. T he increase in CSH diaphragm compliance was observed despite an increa se in the surface area of collagen and was not associated with an abno rmal distribution of titin or laminin.