Abstract 12806: Ca2+ Wave Propagation was Modulated by ROS Generation and Ca2+ Dissociation from the Myofilaments During Stretching in Intact Rat Cardiac Trabeculae
Background: Propagation velocity (Vp) of Ca2+ waves determines delayed afterdepolarization and affects the occurrence of arrhythmias in cardiac muscle. We focused on the initiation mechanism of Ca2+ waves, investigating whether their Vp shows different responses to the changes in force by muscle stretching or by the addition of a paralyzing agent.
Methods: Trabeculae were obtained from 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, 2.0 mM [Ca2+]o). Generation of reactive oxygen species (ROS) was measured with 2’,7’-dichlorofluorescein diacetate (DCF) fluorescence. Ca2+ waves were induced by 2.5-Hz stimulus trains for 7.5 s. Trabeculae were exposed to a jet of solution containing 1) 10 mM Ca2+ (JHC) for the induction of spontaneous Ca2+ release from the sarcoplasmic reticulum in its exposed region, and 2) 5 mM caffeine (JCF) or 0.2 mM Ca2+ (JLC) for Ca2+ dissociation from the myofilaments due to the regional reduction of contractile strength. Ten-percent muscle stretching was applied 10 ms after the last stimulus of the train.
Results: The JHC caused spatially uniform contraction, while the JCF and the JLC caused nonuniform contraction. Muscle stretching increased the rate of change (slope) in the DCF fluorescence and further increased the Vp of Ca2+ waves by the JHC (P<0.05, n=9), the JCF (P<0.05, n=6), and the JLC (P<0.05, n=8). After preincubation with 3 μM diphenyleneiodonium, an inhibitor of NOX generation, or 10 μM colchicine, an inhibitor ofmicrotubule assembly, muscle stretching did not increase the DCF slope nor the Vp of Ca2+ waves only caused by the JHC (n=12), while stretching did increase the Vp by the JCF (P<0.05, n=13) and the JLC (P<0.05, n=7). The addition of 10 μmol/L blebbistatin, a myosin II ATPase inhibitor, reduced developed force to 19.9 ± 2.1%. This reduction did not change the Vp by the JHC (n=17), while it decreased it by the JCF (P<0.01, n=8) and the JLC (P<0.01, n=9) irrespective of preincubation with colchicine.
Conclusions: These results suggest that during stretching, Ca2+ wave propagation can be modulated by ROS generation and be additionally modulated by Ca2+ dissociation from the myofilaments in the case of nonuniform contraction.
- © 2012 by American Heart Association, Inc.