Utilizing a model system for cardiomyopathy a detailed study of the pathophysiology of cardiomyopathy will be studied. The development of cardiomyopathy will be studied temporally by correlating the nature and extent of microvascular lesions with the development of focal myonecrosis and fibrosis in a murine model. Cardiac membranes from each stage of disease will be examined with regard to their functional state and quantity of the B-adrenergic receptor complex. Evidence has been presented to show that B-receptors are altered in cardiomyopathy. Previously we have demonstrated in a continuous line of muscle cells (L6E9) that there is alteration in myogenesis. These observations have led to the present proposal in which we plan to determine the temporal relationship between myocardial injury and B receptor changes; reversibility will be assessed; the precise locus of the effect on the B-adrenergic cyclase unit will be determined. The studies to be carried out will use cell homogenate to determine receptor density and affinity; cyclase activity in response to isoproteronol or forskolin and the IC50 using ICYP will be determined. Studies will be carried out to determine whether these effects are reversible by employing high temperature permissive myoblasts that are restrictive to intracellular parasites. In vivo we will study B-receptor by determining basal and agent stimulated cyclase activity; B-receptor density and affinity; the IC50 for isoproteronol and the effect of GTP on these values. Once we have demonstrated an effect on B-receptor function we will identify the molecular locus of that effect, i.e., R, C, or N units, utilizing a variety of techniques to accurately assess the patency of each structure in the receptor-cyclase complex. These studies may relate to cardiomyopathy in general and may provide a basis for rational therapy.
