AMP stimulation of endocytotic transport from canine coronary circulation into myocytes.

Provision of ATP precursors before, during, and after an episode of myocardial ischaemia accelerates repletion of ATP levels and functional recovery of the tissue. To investigate ultrastructural effects of such provision, canine hearts were perfused in situ with sham and AMP solutions. Perfusion was begun 15 min before induction of ischaemia and continued during the 15 min ischaemic and 15 min reperfusion period. Some hearts were then treated with LaOH to label endocytotic vesicles, and the hearts were fixed for electron microscopy. A dramatic and significant increase was found in the number and size of capillary endothelial and subsarcolemmal vesicles in hearts treated with AMP, but not in hearts treated with sham additives. Endocytosis and exocytosis across capillary endothelia, and endocytosis into myocytes is suggested as a mechanism for rapid transport of ATP precursors from the coronary circulation into myocytes.