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Altered myosin isozyme patterns from pressure-overloaded and thyrotoxic hypertrophied rabbit hearts
Insights
Altered myosin isozyme proportions in cardiac hypertrophy impact heart performance. Pressure overload increases slow myosin (V3), while thyroxine increases fast myosin (V1), affecting cardiac function.
Area of Science:
- Cardiovascular Biology
- Molecular Cardiology
- Protein Biochemistry
Background:
- Cardiac hypertrophy alters myocardial contractility and energy production.
- Myosin isozymes are critical determinants of cardiac muscle performance.
- Previous studies suggest myosin structure changes contribute to altered cardiac function.
Purpose of the Study:
- To investigate myosin isozyme composition in pressure-overloaded and thyrotoxic cardiac hypertrophy in rabbits.
- To analyze structural differences in myosin heavy chains between these hypertrophy models.
- To correlate myosin isozyme changes with functional alterations in cardiac performance.
Main Methods:
- Rabbit models of pressure-overloaded and thyrotoxic cardiac hypertrophy were established.
- Myosin isozymes were separated and quantified using pyrophosphate polyacrylamide gel electrophoresis.
- Alpha-chymotryptic digestion and 14C-iodoacetamide labeling were used to analyze myosin heavy chain structure.
Main Results:
- Normal rabbit hearts predominantly expressed slow myosin (V3).
- Pressure-overload hypertrophy led to a decrease in fast (V1, V2) and an increase in slow (V3) myosin.
- Thyrotoxic hypertrophy resulted in a predominance of fast myosin (V1) with reduced V2 and V3 components.
- Peptide mapping confirmed distinct structural differences in myosin heavy chains between the models.
Conclusions:
- Altered proportions of myosin isozymes are a key feature of different cardiac hypertrophy types.
- Changes in myosin isozyme composition likely underlie the functional deficits observed in pressure-overloaded hearts and enhancements in thyrotoxic hearts.
- Myosin isozyme shifts represent an adaptive or maladaptive response to distinct cardiac stress stimuli.
Abstract:
Cardiac hypertrophy, induced by pressure overload, leads to a depression in the rate of force development, velocity of shortening, tension-dependent heat generation, and myosin ATPase activity, whereas cardiac hypertrophy, induced by thyroxine administration, leads to an increase in these parameters. These changes have been attributed, in part, to structural changes in myosin. In this study, we have investigated changes in the relative content of myosin isozymes and differences in primary structure of the isozymes in pressure-overloaded and thyrotoxic cardiac hypertrophy in the rabbit. Three myosin isozymic forms (V1 = fastest, V2 = intermediate, V3 = slowest mobility) were observed in pyrophosphate polyacrylamide gels from normal hearts with the V3 component being the predominant species. In the pressure-overloaded model, the V1 and V2 components disappeared or were present in reduced amounts leaving the V3 more predominant. The most striking difference was the isozymic profile produced in thyrotoxic hearts where the V1 became the predominant component and V2 and V3 the minor components. alpha-Chymotryptic digestion of myosin heavy chains produced characteristic, reproducible peptide patterns for each of the animal models, as did fluorographic analyses of alpha-chymotryptic digests of 14C-iodoacetamide (IAA)-labeled SH1 peptides of myosin. Our results suggest that altered proportions of myosin isozymes may be responsible for altered cardiac performance.