Regular Article
Ascorbate/Iron Activates Ca2+-Release Channels of Skeletal Sarcoplasmic Reticulum Vesicles Reconstituted in Lipid Bilayers

https://doi.org/10.1006/abbi.1994.1030Get rights and content

Abstract

Ca2+-release channel or ryanodine receptor is known to be involved in physiologic Ca2+-release from sarcoplasmic reticulum in skeletal and cardiac muscle. A variety of chemical oxidants and in particular SH-oxidizing reagents have been shown to activate Ca2+ release. However, the role of the oxidative modification of the channel in the physiologic mechanism(s) of Ca2+ release and in pathologic states of the muscle remains to be elucidated. Ascorbate/iron redox couple is known to be an efficient generator of oxygen radicals and semidehydroascorbyl radicals. Ascorbate/iron was shown to be released from cardiomyocytes during ischemia-reperfusion and was suggested to be involved in the ischemia-reperfusion injury and cardiomyocyte death. To understand the potential contribution of ascorbate/iron to Ca2+ release mechanism(s), calcium release channels from skeletal sarcoplasmic reticulum (SR) were reconstituted in artificial planar bilayers to examine the effects of this redox couple on the channel activity. Ascorbate elicited a transient (about 2 min) but dramatic increase of open-time probability of the channel. At pCa = 7.0, the presence of EGTA blocked ascorbate induced activation of release channels. However, when exogenous iron was added, ascorbate activated Ca2+ release channels, even in the presence of EGTA. ESR measurements demonstrated that semidehydroascorbyl radicals were generated from ascorbate in the absence of EGTA. The semidehydroascorbyl radical ESR signal was quenched by EGTA in the absence (but not in the presence) of exogenous iron. Thus, the production of ascorbyl radicals was associated with increased channel activity. In the presence of heparin, ascorbate plus iron elicited a long-lasting activation of the channel which had conductance gCa2+ = 100 pS characteristic for the ryanodine receptor and which could be blocked by the ryanodine channel inhibitor, ruthenium red. In conclusion the physiologically relevant redox couple - ascorbate/iron - at physiologic concentrations can activate Ca2+ channels in sarcoplasmic reticulum vesicles.

References (0)

Cited by (43)

  • Iron catalysis of lipid peroxidation in ferroptosis: Regulated enzymatic or random free radical reaction?

    2019, Free Radical Biology and Medicine
    Citation Excerpt :

    However, the question of whether Fe-Lb-oxo complexes are formed in cells and contribute to the toxicity of iron remains to be resolved. It should also be mentioned that triggering of lipid peroxidation in ferroptotic cells may be preceded or paralleled by Fe-Ln- or Fe(iv)-Lb-oxo-induced modification of the enzymatic activities of redox-sensitive proteins [125–127]. The nature of the immediate lipid peroxidation products acting as proximate pro-ferroptotic signals still remains to be elucidated.

  • Left Ventricular Systolic Function During Stress Echocardiography Exercise in Subjects With Asymptomatic Hereditary Hemochromatosis

    2006, American Journal of Cardiology
    Citation Excerpt :

    The mechanisms responsible for the finding are not clear at this point. Experimental studies have shown that iron overload15–17 and increased oxidative stress18,19 can alter ion channels and be associated with cardiac arrhythmias. Further investigation of the clinical relevance and mechanistic considerations of this abnormality is warranted.

  • ROS in the local and systemic pathogenesis of COPD

    2003, Free Radical Biology and Medicine
View all citing articles on Scopus
View full text