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Related Experiment Videos

Myofibrillar adaptations during cardiac hypertrophy

R L Toffolo1, C D Ianuzzo

  • 1Department of Physical Education, Faculty of Pure and Applied Science, York University, Toronto, Canada.

Molecular and Cellular Biochemistry
|February 23, 1994
PubMed
Summary

Compensatory hypertrophy in rat hearts involves adaptive changes in cell size and myosin isoforms, progressing transmurally from the endocardium to the epicardium. These adaptations help the left ventricle manage pressure overload.

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Area of Science:

  • Cardiovascular Physiology
  • Cardiac Remodeling
  • Molecular Cardiology

Background:

  • Compensatory hypertrophy is a critical adaptation to sustained pressure overload in the heart.
  • Understanding transmural differences in cellular adaptation is key to comprehending left ventricular (LV) function during hypertrophy.

Purpose of the Study:

  • To investigate transmural adaptive changes in cell size, myofibrils, and myosin isoforms within the rat LV during pressure-induced compensatory hypertrophy.
  • To determine the spatial and temporal progression of these changes from the endocardium (ENDO) to the epicardium (EPI).

Main Methods:

  • Induction of hypertrophy via supra-renal aortic constriction in rats.
  • Analysis of cardiac tissue at 2, 7, 15, and 30 days post-constriction.
  • Measurement of cell cross-sectional area, myofibril (MF) diameter, and myosin isoform distribution (V1 and V3).

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Main Results:

  • Significant left ventricular hypertrophy (63%) observed by 30 days.
  • A transmural gradient in V3 myosin isoform expression was evident early (7 days) and persisted (30 days), with higher levels in the ENDO compared to EPI.
  • Cell cross-sectional area was consistently greater in the ENDO than EPI from 7 to 30 days.
  • Myofibril diameter remained unchanged, but the number of myofibrils per myocyte increased by approximately 70% due to cell hypertrophy.

Conclusions:

  • The adaptive strategy to pressure overload involves initial increases in myocyte cross-sectional area.
  • A subsequent switch in myosin expression from V1 to V3 occurs, progressing transmurally from sub-endocardium to sub-epicardium.
  • These transmural adaptations are crucial for maintaining left ventricular function under chronic pressure overload.