6 research outputs found
Qualitatively different cross-bridge attachments in fast and slow muscle fiber types
Contractile properties differ between skeletal, cardiac and smooth muscles as well as between various
skeletal muscle fiber types. This functional diversity is thought to be mainly related to different speeds
of myosin head pulling cycles, with the molecular mechanism of force generation being essentially the
same. In this study, force-generating attachments of myosin heads were investigated by applying small
perturbations of myosin head pulling cycles in stepwise stretch experiments on skeletal muscle fibers of
different type. Slow fibers (frog tonic and rat slow-twitch) exhibited only a ‘slow-type’ of myosin head
attachment over the entire activation range, while fast fibers (frog and rat fast-twitch) displayed a
‘slow-type’ of myosin head attachment at low levels of activation, and an up to 30-times faster type at
high levels of activation. These observations indicate that there are qualitative differences between the
mechanisms of myosin head attachment in slow and fast vertebrate skeletal muscle fibers