A new cardiac myosin characterized from the canine atria.

Canine atrial myosin light chains were electrophoretically distinct from myosins of canine ventricles on 5–20% polyacrylamide gradient slab gels (SDS), giving molecular weights of 26,000 and 21,000 as compared to 28,000 and 18,500 for ventricular myosin light chains. While atrial myosin heavy chains were immunologically identical with ventricular myosin heavy chains, in contrast, there was 8.0% relative cross-reactivity of atrial myosin light chains with left ventricular myosin light chains by radioimunoassay. According to charge separation on two-dimensional polyacrylamide urea gels, atrial myosin light chains were different from those of ventricular myosins. Variances in ATPase activities between atrial and ventricular myosins were strongly demonstrated. There was a lower K⁺ activated ATPase activity in atrial myosin, however the Ca²⁺ activated ATPase activity, at ATP saturation levels, was higher in atrial myosin as compared to ventricular myosins.