Key result
Myosin from specialized bovine myocardial tissue exhibited Ca2+-activated ATPase activity intermediate between atrial and ventricular myosins and contained light chains of both.
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Warrants no clinical change; leaves open the role of hybrid myosin in specialized cardiac function.
The ATPase activity, light chains and isoenzymes of myosin from specialized myocardial tissue (the A-V node, bundle of His, and right and left bundle branches) of bovine heart were compared with those of atrial and ventricular myosins. The order of Ca2+-activated ATPase activity was atrial greater than specialized myocardial tissue greater than ventricular myosin. SDS-polyacrylamide gel electrophoresis showed that myosin from the specialized myocardial tissue contained the light chains of both atrial and ventricular myosins. On the other hand, the specialized myocardial tissue contained one V3 isomyosin and showed no difference from ventricular myocardial tissue on pyrophosphate gel.
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Tamura et al. (1984) studied this question. Specialized myocardial tissue (A-V node, bundle of His, bundle branches) vs. Atrial and ventricular myosins was evaluated on ATPase activity, light chains and isoenzymes of myosin. Myosin from specialized bovine myocardial tissue exhibited Ca2+-activated ATPase activity intermediate between atrial and ventricular myosins and contained light chains of both.
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