Mitochondrial respiratory chain enzyme activities in tetralogy of Fallot

It has been suggested that myocardial ischemia is associated with a reduction in mitochondrial complex I activity. Respiratory chain enzyme activities were measured in right ventricular biopsies of eight infants with tetralogy of Fallot (TF), left ventricular biopsies of one of the infants with TF, right and left ventricular tissue of seven transplant recipients with atherosclerotic coronary artery disease (CAD), and in right ventricular biopsies of one infant without cardiac pathology (normal control). In right ventricular tissue the specific activity of complexes I+III was significantly lower in TF than in CAD (3.8 +/- 2.7 vs 23 +/- 12 nmol min-1 mg-1 non-collagen protein). In the right ventricular control specimen the activity of complexes I+III was 13.7-fold standard deviation higher than in TF and 1.5-fold higher than in CAD. Left ventricular respiratory chain enzyme activities measured in one patient with TF were lower than those in patients with CAD. Enzyme activities of left ventricular tissue were not significantly different from those of the right ventricle in CAD. The activity of the mitochondrial matrix enzyme citrate synthase did not differ between groups. The data indicate that the prominent reduction of complex I activity found in myocardial ischemia due to CAD is even more pronounced in myocardial hypoxemia due to TF.