In vivo left ventricular functional capacity is compromised in cMyBP-C null mice

Cardiac myosin binding protein-C (cMyBP-C) is a thick filament-associated protein that binds tightly to myosin and has a potential role for modulating myocardial contraction. We tested the hypothesis that cMyBP-C 1) contributes to the enhanced in vivo contractile state following [beta]-adrenergic stimulation and 2) is necessary for myocardial adaptation to chronic increases in afterload. In vivo pressure-volume relations demonstrated that left ventricular (LV) systolic and diastolic function were compromised under basal conditions in cMyBP-[C.sup.-/-] compared with WT mice. Moreover, whereas [beta]-adrenergic treatment significantly improved ejection fraction, peak elastance, and the time to peak elastance in WT mice, these functional indexes remained unchanged in cMyBP-[C.sup.-/-] mice. Morphological and functional changes were measured through echocardiography in anesthetized mice following 5 wk of aortic banding. Adaptation to pressure overload was diminished in cMyBP-[C.sup.-/-] mice as characterized by a lack of an increase in posterior wall thickness, increased LV diameter, deterioration of fractional shortening, and prolonged isovolumic relaxation time. These results suggest that the absence of cMyBP-C significantly diminishes in vivo LV function and markedly attenuates the increase in LV contractility following [beta]-adrenergic stimulation or adaptation to pressure overload. aortic handing; pressure-volume relations; dobutamine