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.