Inhibition of matrix metalloproteinases prevents peroxynitrite‐induced contractile dysfunction in the isolated cardiac myocyte

Background and purpose: The potent oxidant peroxynitrite (ONOO − ) induces mechanical dysfunction in the intact heart in part through activation of matrix metalloproteinase‐2 (MMP‐2). This effect may be independent of the proteolytic actions of MMPs on extracellular matrix proteins. The purpose of this study was to examine the effects of ONOO − on contractile function at the level of the single cardiac myocyte and whether this includes the action of MMPs. Experimental approach: Freshly isolated ventricular myocytes from adult rats were superfused with Krebs–Henseleit buffer at 21 °C and paced at 0.5 Hz. Contractility was measured using a video edge‐detector. ONOO − or decomposed ONOO − (vehicle control) were co‐infused over 40 min to evaluate the contraction cease time (CCT). The effects of ONOO − on intracellular [Ca 2+ ] were determined in myocytes loaded with calcium green‐1 AM. MMP‐2 activity was measured by gelatin zymography. Key results: ONOO − (30‐600 μ M ) caused a concentration‐dependent reduction in CCT. Myocytes subjected to 300 μ M ONOO − had a shorter CCT than decomposed ONOO − (14.9 + 1.5 vs 32.2 + 3.5 min, n =7–8; P <0.05) and showed increased MMP‐2 activity. The MMP inhibitors doxycycline (100 μ M ) or PD 166793 (2 μ M ) reduced the decline in CCT induced by 300 μ M ONOO − . ONOO − caused shorter calcium transient cease time and significant alterations in intracellular [Ca 2+ ] homoeostasis which were partially prevented by doxycycline. Conclusions and implications: This is the first demonstration that inhibition of MMPs protects the cardiac myocyte from ONOO − ‐induced contractile failure via an action unrelated to proteolysis of extracellular matrix proteins. British Journal of Pharmacology (2008) 153 , 676–683; doi: 10.1038/sj.bjp.0707621 ; published online 10 December 2007