Biphasic effect of SIN-1 is reliant upon cardiomyocyte contractile state

• Published in: Free radical biology & medicine Vol. 45; no. 1; pp. 73 - 80
• Main Authors: Kohr, Mark J., Wang, Honglan, Wheeler, Debra G., Velayutham, Murugesan, Zweier, Jay L., Ziolo, Mark T.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.07.2008
• Subjects: Animals; Calcium-Binding Proteins - deficiency; Calcium-Binding Proteins - genetics; Calcium-Binding Proteins - metabolism; Cardiac; Excitation–contraction coupling; Free radicals; Mice; Mice, Knockout; Molsidomine - analogs & derivatives; Molsidomine - pharmacology; Muscle Contraction - drug effects; Myocytes, Cardiac - drug effects; Myocytes, Cardiac - metabolism; Peroxynitrite; Phospholamban; Reactive nitrogen species; β-Adrenergic stimulation; L-NAME; Peroxynitrite; Free radicals; ISO; NOS2; EPR; Cardiac; PLB; Reactive nitrogen species; Phospholamban; SERCA; CONT; SIN-1; NOS; Excitation–contraction coupling; CP-H; FeTPPS; β-Adrenergic stimulation; PLB -; RCL; NOS1; WT; SR
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2008.03.019

Many studies have demonstrated a biphasic effect of peroxynitrite in the myocardium, but few studies have investigated this biphasic effect on β-adrenergic responsiveness and its dependence on contractile state. We have previously shown that high 3-morpholinosydnonimine (SIN-1) (source of peroxynitrite, 200 μmol/L) produced significant anti-adrenergic effects during maximal β-adrenergic stimulation in cardiomyocytes. In the current study, we hypothesize that the negative effects of high SIN-1 will be greatest during high contractile states, whereas the positive effects of low SIN-1 (10 μmol/L) will predominate during low contractility. Isolated murine cardiomyocytes were field stimulated at 1 Hz, and [Ca 2+] i transients and shortening were recorded. After submaximal isoproterenol (ISO) (β-adrenergic agonist, 0.01 μmol/L) stimulation, 200 μmol/L SIN-1 induced two distinct phenomena. Cardiomyocytes undergoing a large response to ISO showed a significant reduction in contractility, whereas cardiomyocytes exhibiting a modest response to ISO showed a further increase in contractility. Additionally, 10 μmol/L SIN-1 always increased contractility during low ISO stimulation, but had no effect during maximal ISO (1 μmol/L) stimulation. SIN-1 at 10 μmol/L also increased basal contractility. Interestingly, SIN-1 produced a contractile effect under only one condition in phospholamban-knockout cardiomyocytes, providing a potential mechanism for the biphasic effect of peroxynitrite. These results provide clear evidence for a biphasic effect of peroxynitrite, with high peroxynitrite modulating high levels of β-adrenergic responsiveness and low peroxynitrite regulating basal function and low levels of β-adrenergic stimulation.