MYOCARDIAL FUNCTIONAL CORRELATES OF CARDIAC MYOSIN LIGHT CHAIN-2 PHOSPHORYLATION

In vitro and in situ studies have proposed a potentiation of submaximal force production after myosin light chain 2 (p-light chain) phosphorylation in mammalian striated muscle. The purpose of this study was to ascertain the relationship between the augmentation in left ventricular pressure development and cardiac myosin P-light chain phosphorylation at different times during and after submaximal treadmill exercise involving adult female Sprague-Dawley rats. In vivo hemodynamic measurements were monitored with an indwelling high-fidelity solid-state pressure transducer. Exercise heart rate, peak left ventricular (LV) pressure, and rate of LV pressure development/relaxation (LV ± dP/dt) were significantly elevated compared with a normal sedentary group (P < 0.001). Peak LV pressure remained significantly elevated throughout 20 min of postexercise recovery (P < 0.01), and heart rate, LV end-diastolic pressure, and LV ± dP/dt returned rapidly to preexercise values. Corresponding to these in vivo hemodynamic changes, increased levels of P-light chain phosphorylation were observed during both exercise (16%, P < 0.01) and subsequent recovery periods (14%, P < 0.02) compared with the NC group. A quasi-temporal relationship was observed between postexercise peak LV pressure potentiation and P-light chain phosphorylation. These results demonstrate that cardiac myosin P-light chain phosphorylation is associated, in part, with the augmentation of peak LV pressure observed during both exercise and recovery.