Comparison of contractile state and myosin isozymes of rat right and left ventricular myocardium

We compared myocardial mechanics and myosin isozymes of right and left ventricular papillary muscles from adult (6 to 8 month old) male rats. Analysis of force velocity relations indicate that right ventricular papillary muscles contract more rapidly than left at light loads (2.68±0.13 vs 2.18±0.07 muscle lengths/s measured 75 ms following stimulation, at 0.5 g/mm²; P<0.01). Right ventricular papillary muscles had significantly more of the α heavy chain containing V₁ myosin isozyme and less of the V₃ containing β heavy chain myosin isozyme than left ventricular preparations (P<0.05). Papillary muscle and ventricular free wall myosin isozyme distribution were not significantly different within their respective chambers. The presence of a relatively larger proportion of the α heavy chain containing myosin isozyme (V₁) in right ventricle papillary muscles relative to left correlated with the more rapid velocities of shortening seen in right ventricular papillary muscles (r=0.60; P<0.01).