Polyamines mediate coronary transcapillary macromolecular transport in the calcium paradox

This study addresses the role of polyamines and their rate limiting enzyme, ornithine decarboxylase in regulation of macromolecular transport of two macromolecules, fluorescein and horseradish peroxidase, across coronary capillaries. Rat hearts were isolated and retrogradely perfused through the aorta (Langendorff method), stabilized by 10 min perfusion with Krebs-Henseleit medium containing Ca2+, followed by 5 min perfusion with Krebs-Henseleit medium without Ca2+ and an additional 30 s to 2 min with Krebs-Henseleit medium containing 1 mg/ml horseradish peroxidase. alpha-Difluoromethylornithine, the only known function of which is inhibition of ornithine decarboxylase, and putrescine were added as needed. Perfusion with Krebs-Henseleit medium without Ca2+ caused a two-fold increase in fluorescein transport but a decrease in horseradish peroxidase transport. Reperfusion with Krebs-Henseleit medium caused a four-fold increase in fluorescein transport and a ten-fold increase in horseradish peroxidase positive intraendothelial cell vesicles over control values. alpha-Difluoromethylornithine inhibited these increases and putrescine negated the alpha-difluoromethylornithine effect. Other morphological measures of horseradish peroxidase transport and associated membrane activities including modulation of endothelial cells luminal and abluminal pits were effected in the same manner. Transport of macromolecules through coronary capillaries, over the short term studied, appears to be regulated by the ornithine decarboxylase/polyamine pathway.