This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Despite advances in biomedicine, the 5-year mortality of heart failure patients remains well above 50%. Mutations in the gene encoding cardiac myosin binding protein-C (cMyBP-C) is the most common cause of hypertrophic cardiomyopathies (HCM), a disease which affects 1 in 1,500 Americans. In addition, the altered phosphorylation of cMyBP-C in heart muscle cells (i.e., myocardium) can contribute to compensatory mechanisms and contractile dysfunction in heritable and acquired myocardial disease. Thus, understanding cMyBP-C's role in modulating contraction could lead to development of new treatments such as gene therapy and drugs controlling the structural dynamics of cMyBP-C to enhance force and pressure generation. We believe cMyBP-C acts to "put the breaks" on the speed of the contracting cycle and releases the break on contraction when phosphorylated. Using the approach of synchrotron x-ray diffraction, we will probe for changes in molecular structure that arises from removing or altering cMyBP-C in genetically-engineered mice. In support of our hypothesis, we have already found profound effects on the myosin protein structure when cMyBP-C is lacking or modified using de-membrantaed myocardium. Our present project efforts focus on using membrane-intact myocardium as it beats in the living heart, in which we will record twitch force and diffraction patterns in between twitches and near maximum twitch force in trabeculae isolated from mouse myocardium electrically stimulated in the presence and absence of a beta-adrenergic-stimulating drug. We hypothesize that treatment will move cross-bridges towards the thin filament before the twitch to accelerate contraction kinetics on contraction.