This project examines mitochondrial functioning in old age and in pathological states in which decreased energy transduction by mitochondria may compromise tissue survival. Experimental results this year derive from two paradigms relating to heart failure and death of cardiac myocytes. (1) We have studied heart contractile performance and mitochondrial metabolism of two strains (B10 14.6 and TO-2) of hamster which serve as models of genetically-determined dilated cardiomyopathy, as well as healthy control animals. The hearts from the B10 14.6 and TO-2 animals developed less pressure than the healthy hearts, as reported previously. In addition, a smaller fraction of pyruvate dehydrogenase was present in the active, dephosphorylated form (PDH A) in the B10 14.6 (45%) and TO-2 (20%) animals, compared to the controls (86%), when the substrate was glucose. The results suggest stable changes in the ratio of pyruvate dehydrogenase kinase: phosphatase activity in both cardiomyopathic strains: in addition, there is a markedly reduced alpha-ketoglutarate dehydrogenase, and thus potential for Krebs cycle oxidation, in the TO-2 animal. (2) We have also initiated a study into the role of mitochondrial energy transduction in ischemic failure, using rat cardiac myocytes as models. Fluorescence of rhodamine 1,2,3 is measured, as indicative of mitochondrial membrane potential (delta psi). Conditions for loading the cells with rhodamine 1,2,3 have been established with cell suspensions: fluorescence microscopy of single cells should allow correlation of changes in contractile state, mitochondrial free calcium and delta psi during simulated ischemia and reperfusion.
