Peroxynitrite-induced cardiac depression:: role of myofilament desensitization and cGMP pathway

Objective: The oxidant species peroxynitrite, the reaction product of nitric oxide (NO.) and superoxide, has been implicated in several pathophysiological conditions of the heart. Here, we studied the mechanism of peroxynitrite-induced cardiac depression using specific drugs and simultaneous analyses of myocardial function and intracellular Ca2+ ([Ca2+](i)). Methods: Rat hearts were perfused retrogradely and left ventricular function (balloon method) and [Ca2+](i) transients were recorded on a beat-to-beat basis using the aequorin bioluminescence method. Peroxynitrite was infused at 10.8 +/- 0.93 muM via sideline for 10 min, followed by a 15-min recovery period to monitor irreversible effects. Test drugs were infused prior to and during peroxynitrite application. Results: Peroxynitrite depressed left ventricular developed pressure (LVDevP; - 40%), yet increased systolic and diastolic [Ca2+](i) (1.3 - and 2.3 - fold, respectively; n = 12). When Ca2+ entry through Ca2+ channels or Na+/Ca2+ exchange transport was blocked using nicardipine (1 muM, n = 3) or dichlorobenzamil (30 muM, n = 5), respectively, cells showed lower [Ca2+](i) and accentuated negative inotropic action in response to peroxynitrite. Peroxynitrite slowed left ventricular relaxation and [Ca2+](i) transients, both of which were not affected by extracellular Ca2+ restriction. Importantly, the oxidant greatly depressed myofilament responsiveness to Ca2+, which was partly antagonized by Rp-8-(4-chlorophenylthio)guanosine-3',5'-cyclic monophosphorothioate (Rp-cGMPS), an inhibitor of cGMP-dependent protein kinase. Also, the inhibitor partially restored left ventricular contractility (n = 6). Peroxynitrite stimulated cardiac cGMP production and coronary cGMP efflux (n = 6). Decomposed peroxynitrite had no effect in any of the tests. Conclusions: Peroxynitrite depresses myocardial contractility by decreasing the ability of Ca 21 to trigger contraction, and this effect is partly mediated by the cGMP/cGMP-dependent protein kinase pathway. (C) 2003 European Society of Cardiology. Published by Elsevier B.V. All rights reserved.