Role of reactive oxygen species and Ca²⁺ dissociation from the myofilaments in determination of Ca²⁺ wave propagation in rat cardiac muscle

Ca²⁺ waves are initiated not only by Ca²⁺ leak from the sarcoplasmic reticulum (SR), but also by Ca²⁺ dissociation from the myofilaments in the myocardium with nonuniform contraction. We investigated whether contractile properties and the production of reactive oxygen species (ROS) affect Ca²⁺ wave propagation. Trabeculae were obtained from 76 rat hearts. Force was measured with a strain gauge, sarcomere length with a laser diffraction technique, and [Ca²⁺]_i with fura-2 and a CCD camera (24°C, 2.0mmol/L [Ca²⁺]_o). ROS production was estimated from 2',7'-dichlorofluorescein (DCF) fluorescence. Trabeculae were regionally exposed to a jet of solution containing 1) 10mmol/L Ca²⁺ to initiate Ca²⁺ waves by SR Ca²⁺ leak due to Ca²⁺ overload within the jet-exposed region, and 2) 0.2mmol/L Ca²⁺ or 5mmol/L caffeine to initiate such waves by Ca²⁺ dissociation from the myofilaments due to nonuniform contraction. Ca²⁺ waves were induced by stimulus trains for 7.5s. Ten-percent muscle stretch increased DCF fluorescence and accelerated Ca²⁺ waves initiated due to both Ca²⁺ overload and nonuniform contraction. Preincubation with 3μmol/L diphenyleneiodonium or 10μmol/L colchicine suppressed the increase in DCF fluorescence but suppressed acceleration of Ca²⁺ waves initiated only due to Ca²⁺ overload. Irrespective of preincubation with colchicine, reduction of force after the addition of 10μmol/L blebbistatin did not decelerate Ca²⁺ waves initiated due to Ca²⁺ overload, while it did decelerate waves initiated due to nonuniform contraction. These results suggest that Ca²⁺ wave propagation is modulated by ROS production through an intact microtubule network only during stretch and may be additionally modulated by Ca²⁺ dissociated from the myofilaments in the case of nonuniform contraction.