Ultrastructural localisation of carnitine acetyltransferase activity in mitochondria of rat myocardium.

The acetyl CoA/CoA ratio is an important regulating factor of beta-oxidation in mitochondria and hence of energy production in the myocardium. Carnitine acetyltransferase provides one of the control mechanisms for this ratio during changing energy demand in the heart muscle, possibly by buffering the CoA and carnitine concentration for sustained beta-oxidation. In search for a possible correlation between the activity of this enzyme and ultrastructural changes in heart mitochondria, carnitine acetyltransferase was cytochemically localised in rat myocardium, brought into different metabolic states. In this work we confirm previous observations, namely the formation of contact sites between inner and outer mitochondrial membranes upon catecholaminergic stimulation of the myocardium. It is further shown that this contact site formation might be a prerequisite for carnitine acetyltransferase to demonstrate enzymatic activity and hence control of beta-oxidation in myocardial mitochondria.