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 f rom 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 two fold with the alpha1-subunit of LCC, the ryanodine receptor calsequest rin, and Na+-K+-adenosinetriphosphatase (ATPase), whereas the contents of these proteins in ventricular homogenates were not different. In c ontrast, Na+-H+ antiporter and sarcoplasmic reticulum (SR) Ca2+-ATPase showed no difference in their contents in both homogenates and micros omes. Radioligand binding assay further showed no significant differen ce in the number of binding sites for [H-3]prazosin, [I-125]iodocyanop indolol, and [H-3]saxitoxin between myopathic and normal microsomes. T hese results suggest that whereas membrane densities of LCC and the ot her 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 m icrosomal fractions from myopathic heart muscle, shows that abnormalit y exists in the mechanical property of cell membrane in the myopathic heart.