Accessibility of Myofilament Cysteines and Effects on ATPase Depend on the Activation State during Exposure to Oxidants
Figure 9
ATPase depends on the contractile state in which myofibrils are exposed to oxidants.
A. ATPase-pCa relationships of rat ventricular myofibrils treated with DTDP (150 µmol/L DTDP) in relaxing or rigor solutions, or untreated (Control). Curves fit to a Hill equation. Values are mean ± SEM; n = 4. Myofibrils treated with DTDP in rigor solution had a markedly higher basal ATPase and significantly higher pCa50 than control values, but maximum ATPase rates were not significantly different from controls. Myofibrils treated with DTDP in relaxing solution had a markedly lower maximum ATPase. B. Normalized ATPase-pCa relationships from control myofibrils and myofibrils treated in activating solution with 75 µmol/L DTDP, 75 µmol/L NEM, or 2 mmol/L SNAP an NO Donor (mean ± SEM; n = 4). NEM induced changes in calcium sensitivity indicating that the changes in ATPase from DTDP treatment were not due to the formation of a disulfide bond. SNAP: the increased calcium sensitivity and basal ATPase from SNAP were due to the modification of cysteines.
