Increased mechanical extraction of T-tubule/junctional SR from cardiomyopathic hamster heart.
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.
Department of Molecular Physiology, National Cardiovascular Center Research Institute, Osaka, Japan.
Y
Y
Tawada-Iwata
T
T
Imagawa
A
A
Yoshida
M
M
Takahashi
H
H
Nakamura
M
M
Shigekawa
D000818:Animals; D015220:Calcium Channels / Q000378:metabolism; D009202:Cardiomyopathies / Q000378:metabolism* / Q000473:pathology; D006224:Cricetinae; D006352:Heart Ventricles; D006652:Histological Techniques; D015151:Immunoblotting; D008024:Ligands; D008647:Mesocricetus; D008861:Microsomes / Q000378:metabolism / Q000648:ultrastructure; D009124:Muscle Proteins / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure; D012016:Reference Values; D019837:Ryanodine Receptor Calcium Release Channel; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D015220:Calcium Channels; D008024:Ligands; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel