Abstract
A recently developed instrument permits tension measurement and length control at such high resolution and frequency bandwidth that it is now possible to obtain static and dynamic mechanical properties of single myofibrils consisting of only 20 to 30 sarcomeres. Isometric tension vs. sarcomere length curves of bull-frog single or double myofibrils were constructed with intracellular solutions having pCa values of 9.0, 6.0, 5.5 and 5.0 at several sarcomere lengths from 2.2 µm to 3.6 µm. Every sarcomere of the myofibril preparation was observable and if a noticeable abnormality in sarcomere length uniformity and A-band misregistration developed, the data were rejected. Good quality single myofibrils produced up to 50 µg active tension which corresponds to about 5 Kg/cm2 (or 50 N/cm2). All active isometric tension vs. sarcomere length curves had positive slopes, i.e. active tension increased with sarcomere length up to 3.6 µm except when pCa was 5.0 in which case the tension measurements at greater sarcomere lengths than 3.0 µm were not possible without compromising the sarcomere uniformity and A-band registration. It was concluded that sarcomeres (both cardiac and skeletal) have an intrinsic property that the active tension increases with sarcomere length within the range of myofilament overlap so long as sarcomeres are activated by submaximal levels of Ca2+ concentration, and that excessive activation leads to misregistration of the A-band which appears to occur due to functional failure of myosin molecules.
Published Version
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