Protein oxidation, tyrosine nitration, and inactivation of sarcoplasmic reticulum Ca2+-ATPase in low-frequency stimulated rabbit muscle.

Sustained contractile activity by chronic low-frequency stimulation in rabbit fast-twitch muscle causes a partial (40-50%) inactivation of the sarcoplasmic reticulum (SR) Ca2+-ATPase and, with prolonged stimulation, a SERCA1a to SERCA2a transition. To investigate the underlying mechanism of the inactivation which precedes the isoform transition, we analyzed SR from 4-day stimulated muscles for Ca2+-ATPase activity, lipid peroxidation, SH and carbonyl groups, and nitrotyrosine. At unaltered SH group and malondialdehyde contents, carbonyl groups were elevated 50% in the SR from stimulated muscles. Immunoblotting with anti-dinitrophenyl and anti-nitrotyrosine antibodies revealed strong labeling of the Ca2+-ATPase, suggesting the inactivation of the enzyme to result from protein oxidation and peroxynitrite-mediated tyrosine nitration.