HUMAN MITOCHONDRIAL-FUNCTION DURING CARDIAC GROWTH AND DEVELOPMENT

Little information is presently available concerning mitochondrial res piratory and oxidative phosphorylation function in the normal human he art during growth and development. We investigated the levels of speci fic mitochondrial enzyme activities and content during cardiac growth and development from the early neonatal period (10-20 days) to adultho od (67 years). Biochemical analysis of enzyme specific activities and content and mitochondrial DNA (mtDNA) copy number was performed with l eft ventricular tissues derived from 30 control individuals. The level s of cytochrome c oxidase (COX) and complex V specific activity, mtDNA copy number and COX subunit II content remained unchanged in contrast to increased citrate synthase (CS) activity and content. The developm ental increase in CS activity paralleled increasing CS polypeptide con tent, but was neither related to overall increases in mitochondrial nu mber nor coordinately regulated with mitochondrial respiratory enzyme activities. Our findings of unchanged levels of cardiac mitochondrial respiratory enzyme activity during the progression from early childhoo d to older adult contrasts with the age-specific regulation found with CS, a Krebs cycle mitochondrial enzyme.