Related Experiment Videos
Oxygen free radicals and calcium homeostasis in the heart
M Kaneko1, Y Matsumoto, H Hayashi
1Third Department of Internal Medicine, Hamamatsu University School of Medicine, Japan.
Insights
Oxygen free radicals cause heart cell calcium overload by disrupting calcium handling. Understanding these effects is crucial for treating oxidative stress in cardiac conditions.
Area of Science:
- Cardiology
- Cell Physiology
- Biochemistry
Background:
- Oxygen free radicals are implicated in cardiac dysfunction.
- Calcium homeostasis is critical for heart function.
- The precise role of oxygen free radicals in cardiac calcium handling remains incompletely understood.
Purpose of the Study:
- To investigate the impact of oxygen free radicals on calcium (Ca2+) homeostasis in cardiac myocytes.
- To elucidate the mechanisms by which oxygen free radicals induce Ca2+ overload.
- To clarify the role of the Na(+)-Ca2+ exchanger in Ca2+ influx under oxidative stress.
Main Methods:
- Review of existing experimental data on oxygen free radicals and cardiac Ca2+.
- Analysis of Ca2+ influx pathways, including Ca2+ channels and the Na(+)-Ca2+ exchanger.
- Examination of the effects on ion transport proteins like Na(+)-K+ ATPase and sarcolemmal Ca(2+)-pump ATPase.
- Assessment of Ca2+ handling by the sarcoplasmic reticulum.
Main Results:
- Excess oxygen free radicals lead to Ca2+ overload in heart cells.
- Ca2+ influx via Ca2+ channels does not increase, but ATP-independent binding rises.
- Oxygen free radicals inhibit Na(+)-K+ ATPase and Na(+)-H(+) exchange, with unclear effects on intracellular Na(+).
- Sarcolemmal Ca(2+)-pump ATPase activity is depressed, reducing Ca2+ extrusion.
- Ca2+ release from sarcoplasmic reticulum is promoted, while sequestration is inhibited.
Conclusions:
- Oxygen free radicals disrupt cardiac Ca2+ homeostasis, causing overload.
- Multiple mechanisms contribute to Ca2+ overload, including impaired Ca2+ extrusion and altered sarcoplasmic reticulum function.
- Further research is needed to fully understand the Na(+)-Ca2+ exchanger's role in oxidative stress-induced Ca2+ influx.
Abstract:
Many experiments have been done to clarify the effects of oxygen free radicals on Ca2+ homeostasis in the hearts. A burst of oxygen free radicals occurs immediately after reperfusion, but we have to be reminded that the exact levels of oxygen free radicals in the hearts are yet unknown in both physiological and pathophysiological conditions. Therefore, we should give careful consideration to this point when we perform the experiments and analyze the results. It is, however, evident that Ca2+ overload occurs when the hearts are exposed to an excess amount of oxygen free radicals. Through ATP-independent Ca2+ binding is increased, Ca2+ influx through Ca2+ channel does not increase in the presence of oxygen free radicals. Another possible pathway through which Ca2+ can enter the myocytes is Na(+)-Ca2+ exchanger. Although, the activities of Na(+)-K+ ATPase and Na(+)-H(+) exchange are inhibited by oxygen free radicals, it is not known whether intracellular Na(+) level increases under oxidative stress or not. The question has to be solved for the understanding of the importance of Na(+)-Ca2+ exchange in Ca2+ influx process from extracellular space. Another question is 'which way does Na(+)-Ca2+ exchange work under oxidative stress? Net influx or efflux of Ca2+?' Membrane permeability for Ca2+ may be maintained in a relatively early phase of free radical injury. Since sarcolemmal Ca(2+)-pump ATPase activity is depressed by oxygen free radicals, Ca2+ extrusion from cytosol to extracellular space is considered to be reduced. It has also been shown that oxygen free radicals promote Ca2+ release from sarcoplasmic reticulum and inhibit Ca2+ sequestration to sarcoplasmic reticulum. Thus, these changes in Ca2+ handling systems could cause the Ca2+ overload due to oxygen free radicals.