Effects of hydroxyl radical induced-Injury in atrial versus ventricular myocardium of dog and rabbit

Aim: Despite the widespread use of ventricular tissue in the investigation involving hydroxyl-radical (OH*) injury, one of the most potent mediators in ischemia-reperfusion injury, little is known about the impact on atrial myocardium. In this study we thus compared the OH*-induced injury response between atrial and right ventricular muscles from both rabbits and dogs under identical experimental conditions. Methods: Small, contracting ventricular and atrial rabbit and dog trabeculae were directly exposed to OH*, and contractile properties were examined and quantified. Results: A brief OH* exposure led to transient rigor like contracture with marked elevation of diastolic tension and depression of developed force. Although the injury response showed similarities between atrial and ventricular myocardium, there were significant differences as well. In rabbit atrial muscles, the development of the contracture and its peak was much faster as compared to ventricular muscles. Also, at the peak of contracture, both rabbit and dog atrial muscles show a lesser degree of contractile dysfunction. Conclusion: These results indicate that both atrial and ventricular muscles develop a rigor like contracture after acute OH*-induced injury, and atrial muscles showed a lesser degree of contractile dysfunction. Comparison of dog versus rabbit tissue shows that the response was similar in magnitude, but slower to develop in dog tissue

Impairment of Diastolic Function by Lack of Frequency-Dependent Myofilament Desensitization in Rabbit Right Ventricular Hypertrophy

Background-Ventricular hypertrophy is a physiological response to pressure overload that, if left untreated, can ultimately result in ventricular dysfunction, including diastolic dysfunction. The aim of this study was to test the hypothesis that frequency-dependent myofilament desensitization, a physiological response of healthy myocardium, is altered in hypertrophied myocardium. Methods and Results-New Zealand white rabbits underwent a pulmonary artery banding procedure to induce pressure overload. After 10 weeks, the animals were euthanized, hearts removed, and suitable trabeculae harvested from the free wall of the right ventricle. Twitch contractions, calibrated bis-fura-2 calcium transients, and myofilament calcium sensitivity (potassium contractures) were measured at frequencies of 1, 2, 3, and 4 Hz. The force frequency response, relaxation frequency response, and calcium frequency relationships were significantly blunted, and diastolic tension significantly increased with frequency in the pulmonary artery banding rabbits compared with sham-operated animals. Myofilament calcium sensitivity was virtually identical at 1 Hz in the treatment versus sham group (pCa 6.11 ± 0.03 versus 6.11 ± 0.06), but the frequency-dependent desensitization that takes place in the sham group (ΔpCa 0.14±0.06, P\u3c0.05) was not observed in the pulmonary artery banding animals (ΔpCa 0.02±0.05). Analysis of myofilament protein phosphorylation revealed that the normally observed frequency-dependent phosphorylation of troponin-I is lost in pulmonary artery banding rabbits. Conclusions-The frequency-dependent myofilament desensitization is significantly impaired in right ventricular hypertrophy and contributes to the frequency-dependent elevation of diastolic tension in hypertrophy