Imaging ATP Consumption in Resting Skeletal Muscle: One Molecule at a Time

Abstract

Muscle contraction is driven by sarcomere shortening and powered by cyclic hydrolysis of ATP by myosin molecular motors. However, myosin in relaxed muscle continues to slowly hydrolyze ATP, analogous to an idling engine. Utilizing super-resolution microscopy to directly image single molecule fluorescent ATP turnover in relaxed rat soleus skeletal muscle sarcomeres, we observed two rates of myosin ATP consumption that differed 5-fold. These distinct hydrolysis rates were spatially segregated, with the slower or "super relaxed" rate localized predominantly to the sarcomere C-zone, where Myosin Binding Protein-C (MyBP-C), a known modulator of muscle contractile function, exists. This super relaxed hydrolysis rate and its location suggest that MyBP-C can sequester myosin motors to regulate muscle metabolism and heat production in resting muscle and force generation upon activation. One Sentence SummarySuper relaxed skeletal muscle myosin is stabilized by Myosin-Binding Protein C as imaged by single ATP molecule consumption.