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Increased mechanical extraction of T-tubule/junctional SR from cardiomyopathic hamster heart
Y Tawada-Iwata1, T Imagawa, A Yoshida
1Department of Molecular Physiology, National Cardiovascular Center Research Institute, Osaka, Japan.
Insights
Myopathic hamster hearts show altered membrane protein content in specific cell fractions, suggesting mechanical property abnormalities in cardiomyopathic heart cells. This impacts L-type calcium channels and other key proteins.
Area of Science:
- Cardiovascular Biology
- Cellular Physiology
- Biochemistry
Background:
- Cardiomyopathy involves cellular and molecular changes affecting heart function.
- Membrane protein composition is crucial for cardiomyocyte excitation-contraction coupling.
Purpose of the Study:
- To investigate the differential expression of L-type calcium channels (LCC) and other membrane proteins in cardiomyopathic versus normal hamster hearts.
- To explore potential alterations in membrane mechanical properties contributing to cardiomyopathy.
Main Methods:
- Quantitative immunoblot assay to determine protein content in ventricular homogenates and microsomes.
- Radioligand binding assays to assess receptor binding sites.
- Comparison between Syrian cardiomyopathic (Bio 14.6) and normal hamsters.
Main Results:
- Myopathic microsomes showed a twofold enrichment of LCC alpha 1-subunit, ryanodine receptor calsequestrin, and Na(+)-K(+)-adenosinetriphosphatase (ATPase) compared to normal controls.
- Ventricular homogenates did not show differences in these proteins.
- No significant differences were observed for Na(+)-H+ antiporter and SR Ca(2+)-ATPase, or in radioligand binding sites.
Conclusions:
- Increased yield of microsomal fractions from myopathic hearts suggests altered mechanical properties of the cell membrane.
- T-tubule/junctional SR membranes are more easily extracted from cardiomyopathic cardiomyocytes.
- These findings indicate abnormalities in the mechanical properties of the myopathic heart cell membrane, rather than increased membrane protein density.
Abstract:
We determined the contents of L-type calcium channels (LCC) and other membrane proteins in ventricular homogenates and microsomes prepared from hearts of 30- to 70-day-old Syrian cardiomyopathic (Bio 14.6) and normal hamsters. Quantitative immunoblot assay revealed that myopathic microsomes, as compared with normal controls, were enriched about twofold with the alpha 1-subunit of LCC, the ryanodine receptor calsequestrin, and Na(+)-K(+)-adenosinetriphosphatase (ATPase), whereas the contents of these proteins in ventricular homogenates were not different. In contrast, Na(+)-H+ antiporter and sarcoplasmic reticulum (SR) Ca(2+)-ATPase showed no difference in their contents in both homogenates and microsomes. Radioligand binding assay further showed no significant difference in the number of binding sites for [3H]prazosin, [125I]iodocyanopindolol, and [3H]saxitoxin between myopathic and normal microsomes. These result suggest that whereas membrane densities of LCC and the other proteins examined are not increased in myopathic cardiomyocytes, T-tubule/junctional SR membranes are more easily extracted from them by mechanical disruption. This, together with 1.5-fold higher yield of microsomal fractions from myopathic heart muscle, shows that abnormality exists in the mechanical property of cell membrane in the myopathic heart.