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Remodeling of myocyte dimensions in hypertrophic and atrophic rat hearts
S E Campbell1, B Korecky, K Rakusan
1Department of Physiology, University of Ottawa Health Sciences Center, Ontario, Canada.
Insights
Cardiac remodeling varies with load changes. Smaller heart cells (myocytes) grow most, while larger ones shrink most, affecting ventricular wall structure and function.
Area of Science:
- Cardiovascular Biology
- Cardiac Physiology
- Cellular Remodeling
Background:
- Hemodynamic load significantly impacts cardiac myocyte size and distribution.
- Regional variations in myocyte dimensions exist within the ventricular wall.
- Understanding these changes is crucial for comprehending cardiac adaptation and disease.
Purpose of the Study:
- To investigate regional changes in cardiac myocyte size and distribution under different load conditions (hypertrophy and atrophy).
- To compare the effects of volume-pressure overload (T3 treatment) and pressure overload (aortic constriction) on myocyte dimensions.
- To analyze the cellular basis of cardiac atrophy induced by heterotopic isotransplantation.
Main Methods:
- Induction of cardiac hypertrophy via 3,3',5-triiodo-L-thyronine (T3) treatment and aortic constriction in rats.
- Induction of cardiac atrophy through heterotopic isotransplantation in rats.
- Isolation of ventricular myocytes using in vitro collagenase perfusion.
- Measurement of cell volume, cell length (image analysis), and estimation of cross-sectional area.
Main Results:
- Myocyte hypertrophy (aortic constriction, T3) primarily increased cross-sectional area, with greater response in the right ventricle and epimyocardium of the left ventricle.
- Smaller myocytes showed the greatest increase in size during hypertrophy.
- Cardiac atrophy led to proportional decreases in cell length and cross-sectional area, predominantly affecting larger myocytes in the left ventricular endomyocardium.
Conclusions:
- Diverse hemodynamic alterations induce distinct myocyte population remodeling patterns across the ventricular wall.
- Smaller myocytes possess greater growth potential, whereas larger myocytes are more susceptible to atrophy.
- These findings highlight the differential cellular responses contributing to cardiac adaptation and maladaptation.
Abstract:
Changes in hemodynamic load cause alterations in cardiac myocyte size, with regional variations in myocyte size distribution possible within the ventricular wall. We studied regional changes in cellular dimensions and their distribution in two models of cardiac hypertrophy and in cardiac atrophy in the rat. Combined volume-pressure overload was produced by 3,3',5-triiodo-L-thyronine (T3) treatment; atrophy was produced by heterotopic isotransplantation. Our previous data from long-term pressure overload after aortic constriction were used for comparison. Isolated ventricular myocytes were obtained after in vitro coronary perfusion with collagenase. Cell volume and its distribution were determined; cell length was directly measured by image analysis, and cross-sectional area was estimated from the cell volume/cell length ratio, assuming a cylindrical model. Myocyte hypertrophy resulting from hyperthyroidism and aortic constriction was primarily due to increased cross-sectional area. In both cases, the relative response was greater in the right ventricle than in the left ventricle. Within the left ventricle, epimyocardial myocytes enlarged the most. Aortic constriction and T3 treatment predominantly increased the size of smaller myocytes. Heterogeneity in myocyte size increased after constriction but remained relatively unaffected after T3 treatment. Atrophy of left ventricular myocytes was due to a proportional decrease in cell length and cross-sectional area, with the greatest decrease in the left ventricular endomyocardium. Atrophy predominantly affected larger myocytes, resulting in a more homogeneous overall population of smaller myocytes. We conclude that various alterations in load lead to diverse remodeling in the myocyte population throughout the ventricular wall. In general, smaller myocytes show the highest growth potential, whereas larger myocytes exhibit the highest potential to atrophy.