Copyright © 2005, European Society of Cardiology
Peroxynitrite-induced 
-actinin nitration and contractile alterations in isolated human myocardial cells
aDivision of Clinical Physiology, Institute of Cardiology, UD MHSC, P.O. Box 1, H-4004 Debrecen, Hungary
bDepartment of Medical Chemistry, UD MHSC, P.O. Box 1, H-4004 Debrecen, Hungary
cUSZ Department of Pharmacology and Pharmacotherapy, P.O. Box 427, H-6701 Szeged, Hungary
dLaboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, P.O. Box 7057, 1007 MB Amsterdam, The Netherlands
* Corresponding author. Tel./fax: +36 52 414928. Email address: pappz{at}jaguar.unideb.hu
Objective: Peroxynitrite-mediated myocardial protein nitration has been associated with a depressed cardiac pump function. In the present study, an attempt was made to elucidate the molecular background of peroxynitrite-evoked alterations in the human myocardium.
Methods: Isometric force generation was measured in permeabilized human ventricular myocytes and biochemical methods were employed to identify the proteins affected by peroxynitrite-induced nitrotyrosine formation.
Results: The maximal Ca2+-activated isometric force (pCa=4.75) decreased to zero with increasing concentrations of peroxynitrite in a concentration-dependent manner (IC50: 55 ± 4 µM; based on a total of 75 myocytes). However, there were no differences before and after the application of 50 µM peroxynitrite in the Ca2+-sensitivity of force production (pCa50: 5.89 ± 0.02 and 5.86 ± 0.04), in the steepness of the Ca2+-force relationship (nHill: 2.22 ± 0.11 and 2.42 ± 0.25), and in the actin–myosin turnover kinetics (ktr at saturating [Ca2+]: 1.14 ± 0.03 1/s and 1.05 ± 0.07 1/s) (P>0.05). Nevertheless, 50 µM peroxynitrite greatly deteriorated the cross-striation pattern and induced a slight, but significant, increase in the passive force component (from 2.1 ± 0.1 to 2.5 ± 0.2 kN/m2; n = 57 cells), reflecting ultrastructural alterations. Western immunoblots revealed that 50 µM peroxynitrite selectively induced the nitration of a protein with an apparent molecular mass of about 100 kDa. Subsequent immunoprecipitation assays identified this nitrated protein as 
-actinin, a major Z-line protein.
Conclusions: These results suggest -actinin as a novel target for peroxynitrite in the human myocardium; its nitration induces a contractile dysfunction, presumably by decreasing the longitudinal transmission of force between adjacent sarcomeres.
KEYWORDS Myocytes; Contractile function; Peroxynitrite; -Actinin; Human myocardium
Time for primary review 27 days
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