Vanadare and phosphate ions reduce tension and increase cross-bridge kinetics in chemically skinned heart muscle

Tension development, immediate stiffness and ATPase of chemically skinned myocardial strips were measured in solutions with varying concentrations of phosphate (P_i) or vanadate (predominantly H₂VO₄^? at pH 7) ion. Vanadate and P_i decreased stiffness in proportion to tension. The results show that, like P_i, vanadate accelerates the turnover rate of cross-bridges, but is effective at about 1/500 the concentration required for the P_i effect. Both P_i and vanadate increased the energy cost of isometric tension maintenance (that is, the ratio of ATPase to tension) and increased the velocity of delayed tension development following quick stretch of the chemically skinned myocardial strips. The results also show that changes in the rate of rise of delayed tension during stretch activation probably reflect changes in the kinetics of the biochemical cycle of the cross-bridges.