Myocyte‐specific overexpression of NOS3 prevents endotoxin‐induced myocardial dysfunction in mice

To learn the impact of myocardial NOS3 during sepsis, effects of myocyte-specific overexpression of NOS3 (msNOS3TG) on endotoxin (ETX)-induced cardiac dysfunction were studied. In vivo cardiac function was examined with echocardiography after challenge with saline (C) or ETX (L: 0111:B4 E. coli LPS, 50 mg/kg) in wild type mice (WT) and mice with msNOS3TG (TG). Cell shortening (CS) and [Ca2+]i were measured in isolated myocytes. Myofilament sensitivity to Ca2+ was determined in skinned myocytes by measuring the change in sarcomere length (ΔSL) in response to pCa 5,5. Myocardial oxidative stress was estimated using fluoroprobe dihydroethidium (DHE). ETX decreased LV fractional shortening (FS) in WTL but not in TGL. While [Ca2+]i transients were depressed similarly by ETX in both genotypes, %CS was depressed only in WTL myocytes. ΔSL was greater in skinned TGL myocytes than in WTL myocytes suggesting greater myofilament sensitivity to Ca2+ in TGL. A thiol reducing agent, dithiothreitol, augmented the Ca2+ sensitivity in skinned WTL but not in TGL myocytes, suggesting that NOS3 prevents myofilament thiol modification. ETX increased the frequency of DHE stained nuclei in cardiac sections from WTL but not TGL. In conclusion, msNOS3TG prevented ETX-induced myocardial dysfunction by enhancing myofilament sensitivity to Ca2+ possibly via reduction of cardiac oxidative stress. Supported by NIH HL-71987.