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Sliding velocity of isolated rabbit cardiac myosin correlates with isozyme distribution



Sliding velocity of isolated rabbit cardiac myosin correlates with isozyme distribution



American Journal of Physiology 263(2 PART 2): H464-H472



To investigate the relationship between the mechanical and biochemical properties of cardiac myosin, the sliding velocity of isolated cardiac myosin obtained from both euthyroid and hyperthyroid rabbits on actin cables was measured with an in vitro motility assay system. Ten rabbits (T) were treated with L-thyroxine to induce hyperthyroidism, and eight nontreated animals (N) were used as controls. Myosin was purified from the left ventricles of anesthetized animals. Myosins isozyme content was analyzed by the pyrophosphate gel electrophoresis method, and myosin adenosinetriphosphatase (ATPase) activity was determined on the same sample. Long well-organized actin cables of green algae, Nitellopsis, were used in the in vitro motility assay. Small latex beads were coated with purified cardiac myosin and introduced onto the Nitellopsis actin cables. Active unidirectional movement of the beads on the actin cables was observed under a photomicroscope, and the velocity was measured. The velocity was dependent on ATP concentrations, and the optimal pH for bead movement was .apprx.7.0-7.5. The mean velocity was higher in T than in N (0.66 .+-. 0.12 vs. 0.32 .+-. 0.09 .mu.m/s, P < 0.01). Both Ca2+-activated ATPase activity and the percentage of .alpha.-myosin heavy chain were also higher in T than in N (0.691 .+-. 0.072 vs. 0.335 .+-. 0.072 .mu.M Pi .cntdot. mg-1 .cntdot. min-1, P < 0.01, and 79 .+-. 12 vs. 26 .+-. 7%, P < 0.01, respectively). The velocity of myosin closely correlated with both Ca2+-activated myosin ATPase activity (r = 0.87, P < 0.01) and the percentage of .alpha.-myosin heavy chain (r = 0.87, P < 0.01).

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Accession: 007798486

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PMID: 1387292



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