An industrial collaboration to develop new microscopy tools to image ATP usage in muscle

Cardiac muscle contraction occurs when myosin II in the thick
filament uses ATP to power the relative movement of the actincontaining thin filament. Given the vast numbers of myosin
motors, if all were active, the heart would be rapidly drained of
ATP. Therefore, to save energy, myosin can enter the 'super
relaxed (SRX)' state when detached from actin, which has an
inhibited ATPase. When needed, e.g., during exercise, these
SRX myosins can be reactivated. Hypertrophic cardiomyopathy
(HCM), the most common genetic heart disease, is thought to be
due to hypercontractility, which may be caused by underpopulation of SRX. We will investigate how SRX is regulated in
both relaxed and active conditions.
Our approach is to study myosin and actin in their native
myofibril environment. This highly ordered structure is capable of
contracting in the presence of calcium and ATP. In this project,
we will construct a device that uses glass microneedles to grab
either end of a myofibril, this will enable the contractile force to
be measured. Uniquely, we will combine this with single
molecule imaging of ATP being turned over in the myofibrils of
porcine/human cardiac muscle, and stem-cell derived
cardiomyocytes. This has not been achieved before and opens
up a huge possibility for understanding how muscle is affected
by calcium, phosphorylation, force, pharmacological
interventions, and disease-associated mutations. By the end of
this project, we will provide a comprehensive understanding of
the role and regulation of myosin's SRX states in normal and
diseased tissue.