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[Biologist's view on diastolic dysfunction]
1U 127, INSERM, hôpital Lariboisière, Paris.
Insights
Ventricular filling relies on active relaxation, passive wall compliance, and atrial contraction. Impaired relaxation in hypertrophy is linked to reduced ATP and altered calcium handling, affecting cardiac function.
Area of Science:
- Cardiology
- Molecular Biology
- Physiology
Background:
- Ventricular filling is crucial for cardiac function, involving relaxation and diastolic phases.
- Abnormalities in these phases can lead to various cardiovascular pathologies.
- Understanding the molecular mechanisms governing these processes is key to addressing cardiac dysfunction.
Purpose of the Study:
- To elucidate the key factors regulating ventricular filling.
- To explain the molecular basis of diastolic dysfunction, particularly in cardiac hypertrophy.
- To identify the roles of ATP, calcium, collagen, and atrial myosine in cardiac adaptation.
Main Methods:
- Review of modern biological explanations for relaxation and diastolic abnormalities.
- Analysis of the roles of ATP concentration and cytoplasmic calcium in active relaxation.
- Examination of passive wall compliance influenced by collagen, aldosterone, and angiotensin II.
- Investigation of atrial contraction mechanisms, including atrial size and isomyosine content.
Main Results:
- Ventricular filling depends on active relaxation (ATP-dependent calcium elimination), passive wall compliance (collagen-regulated), and atrial contraction (atrial size and myosine content).
- In cardiac hypertrophy, reduced ATP and impaired sarcoplasmic reticulum Ca2+ ATPase and Na+/Ca2+ pump activity hinder active relaxation.
- Atrial overload adapts through changes in isomyosine, leading to a slower myosine form.
Conclusions:
- Active relaxation is primarily governed by ATP levels and efficient calcium handling via sarcoplasmic reticulum Ca2+ ATPase and Na+/Ca2+ pump.
- Passive wall compliance is modulated by myocardial collagen content, influenced by hormones like aldosterone and angiotensin II.
- Atrial contraction adapts to overload by altering isomyosine, demonstrating a compensatory mechanism in cardiac function.
Abstract:
Modern biology provides satisfactory explanations for the abnormalities of the different phases of relaxation and diastole. Ventricular filling depends on three factors: active relaxation; the only factor is the concentration of ATP which has to re-increase. This requires elimination of the cytoplasmic calcium which activates ATP-ase by the Ca2+ ATPase of the sarcoplasmic reticulum and the Na+/Ca2+ pump. In hypertrophy, the concentration of the first and the activity of the second are decreased; passive wall compliance, which depends on the quantity and quality of parietal collagen. This factor is partially regulated in the myocardium by the concentration of aldosterone and angiotensin II; atrial contraction, which depends on the size of the atria and their isomyosine content. This changes in atrial overload to a slow form of myosine, one of the mechanisms of adaptation.