Skeletal Respiratory Muscle in a Model of Chronic Obstructive Pulmonary Disorder

Abstract

In Chronic Obstructive Pulmonary Disorder (COPD), mechanical deformations or work overload of the respiratory skeletal muscles may lead to adaptive or maladaptive muscle responses. Sarcomeric deletion, myosin type changes and metabolic alterations have all been observed in respiratory muscles. While the diaphragm has been extensively studied, other respiratory muscles have not been closely examined in this context. Here we apply a new technique for generating primary cultures of intercostal muscle (ITC) fibers to an established mouse model of COPD, thus isolating changes in individual muscle fibers from the general defects in pulmonary function known to occur in COPD. Single ITC fibers were enzymatically dissociated and either loaded with fluorescent calcium indicators or mounted using a novel muscle stretch tool to measure their length-tension relationship as well as passive tension over sarcomere length. Using the ratiometric indicator indo-1, we found a substantial reduction in peak calcium of action potential induced calcium transients in COPD ITC (405/485 ratio; 1.22 vs. 0.95, p=0.003 vs control), but no significant changes in resting calcium concentration (p=0.33). Data taken with MagFluo-4 agree qualitatively with the indo-1 data and show a shortening of the overall decay phase in the ITC fibers of COPD animals. To our knowledge, these data represent the first ex-vivo assessment of the intercostal muscles in COPD. Supported by NIH Grants R01-AR056477, R01-AR055099, T32-AR007592 and T32-HL072751.