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Cardiac myosin: preparation, ATPase in chronic heart hypertrophy
Insights
Chronic heart failure in rabbits shows decreased myosin CaATPase activity. This defect in cardiac myosin function is linked to heart hypertrophy but its cause remains unclear, suggesting myosin abnormality.
Area of Science:
- Biochemistry
- Cardiovascular Physiology
- Molecular Biology
Background:
- Chronic heart hypertrophy is associated with reduced myofibrillar ATPase activity.
- The underlying biochemical mechanisms of this cardiac defect are not fully understood.
Purpose of the Study:
- To investigate the biochemical basis of decreased cardiac myosin ATPase activity in chronic aortic insufficiency (CAI).
- To analyze the properties of myosin and its subunits in experimental heart hypertrophy.
Main Methods:
- Studied three different preparations of heart myosin, assessing purity via MgATPase activity and polyacrylamide gel electrophoresis.
- Measured heart myosin CaATPase activity at different ionic strengths (0.6 and 0.06) in rabbits with CAI.
- Analyzed myosin light subunits using gel electrophoresis to determine molecular weight and charge.
Main Results:
- Heart myosin CaATPase activity was significantly decreased in rabbits with CAI across all myosin preparations.
- Analysis revealed normal charge and molecular weight for two light myosin subunits in CAI.
- No evidence of myosin inhibitors or abnormalities in the nucleoprotein fraction was found.
Conclusions:
- The study indicates that myosin itself is abnormal in chronic aortic insufficiency, leading to reduced CaATPase activity.
- This myosin abnormality contributes to the pathogenesis of chronic heart hypertrophy.
- Further research is needed to elucidate the precise molecular alterations in cardiac myosin.
Abstract:
A low myofibrillar ATPase seems to be established definitely in several experimental models of chronic heart hypertrophy as well as in humans, but the biochemical pathogenesis of this defect is still unclear. Three different preparations of myosin were studied. Their purity was estimated by measuring MgATPase or by polyacrylamide gel electrophoresis. The first preparation was highly contaminated by actin and tropomyosin; the second was rather pure, and the third (chromatography on DEAE-Sephadex) was pure but slightly denaturated. Heart myosin CaATPase (ionic strength 0.6 or 0.06) was decreased in chronic aortic insufficiency in the rabbits (CAI) when all three preparations were tested. Two (molecular weight 18,000 and 26,000), sometimes three light subunits were found in heart myosin. Their charge and molecular weight are normal in CAI. The third subunit (molecular weight 15,500) was found in control as well as in CAI. Search for an inhibitor was unsuccessful since the two myosin ATPases are additive. The nucleoprotein peak separated from myosin during chromatography was identical in control and CAI. Therefore, myosin seems to be abnormal in CAI.