Reduced Unloaded Sarcomere Shortening Velocity and a Shift to a Slower Myosin Isoform

Abstract We developed a mouse myocardial preparation to study cellular dysfunction in acute coxsackievirus myocarditis. Thin right ventricular papillary muscles from normal mice (n=8) were compared with muscles from mice 7 days after coxsackievirus infection (n=7). Sarcomere shortening was studied with laser diffraction (HeNe, A=623.8 nm). A servo-motor was used to shorten a muscle until slack early in isometric contraction. Unloaded sarcomere shortening veloc-ity (VJ) was measured at the start of zero force at slack length. VO was independent of the extent of slack release and was the same as that estimated with an isotonic force-sarcomere shortening velocity relation. Resting muscle stiffness was cal-culated from shortening perturbations in resting muscles. The histology of some papillary muscles (normal, n=4; infected, n=3) was studied. There was no ventricular hypertrophy