Fig. 4. (A ) Representative saturation binding of 3H-ryanodine to a homogenate of left ventricular tissue of a patient with dilated cardiomyopathy as a function of increasing 3H-ryanodine concentrations. Binding was performed at 7 concentrations of 3H-ryanodine ranging from 0.5 to 38 nm in the absence (total binding) and in the presence (nonspecific binding) of 10 μm unlabeled ryanodine to determine specific binding. Free Ca2+concentration was 10−5m. (B ) Scatchard analysis of specific 3H-ryanodine binding of the experiment shown in (A ). The ratio of specifically bound 3H-ryanodine to free 3H-ryanodine is plotted as a function of specifically bound 3H-ryanodine. (C ) Bell-shaped pattern of Ca2+-dependent 3H-ryanodine binding to a homogenate of the same specimen. Binding was performed at a saturating concentration of 3H-ryanodine (12 nm).