Effect of reduced energy metabolism and reperfusion on the permeability and morphology of the capillaries of an isolated rete mirabile.

Abstract

The effects of reduction in energy metabolism were explored in the eel rete mirabile, an organ composed predominantly of capillaries. In vitro experiments showed that glycolysis is the major pathway of energy production in this capillary tissue, and that iodoacetate, KCN, and low PO j in combination markedly reduce its ATP generation. When in situ energy generation was inhibited by this combination during countercurrent perfusion of the arterial and venous capillaries of the rete, an approximate doubling of the intercapillary barrier permeability for human [lu I]albumin, [ l4 C]sucrose, and n Na was found. Structural damage was evident, but the intercellular junctions remained intact. The effect of cessation of flow for 30 minutes, followed by reperfusion, was then explored. Stasis alone altered the structure, chiefly of the venous capillary endothelium, but not the permeability of the intercapillary barrier. Stasis with a hypoxic medium containing the inhibitors of energy generation, followed by reperfusion with oxygenated control medium, resulted in a progressive breakdown of the intercapillary barrier, with a threefold to fourfold increase in solute (labeled albumin, sucrose, and sodium) permeability, evolving during early reperfusion, but no change for labeled water permeability. Morphologically, the endothelial cells, especially those in venous capillaries, showed substantial damage; they appeared vacuolated, their cytoplasm was extracted, and cytoplasmic and membrane debris were found in the lumen; intercellular junctions remained intact. Local pericyte detachment with interstitial edema also appeared. Thus, stasis and reperfusion amplified the effects of reduction in energy generation and hypoxia on both permeability and morphological change.

Changes in the Actin Cytoskeleton of Cardiac Capillary Endothelial Cells during Ischaemia and Reperfusion: The Effect of Phalloidin on Cell Shape

“…We were able to inhibit the development of the double ring pattern by perfusing the capillary bed with phalloidin prior to ischaemia. Phalloidin enhances actin polymerisation, stabilises actin filaments [20, 21, 34]and has been shown not to affect endothelial cell viability, growth or metabolism [16, 17, 22]. Phalloidin does not target β-actin [8, 28, 35].…”

“…Other evidence, including the initiation of a reorganisation of the cell surface area by various vasoactive substances, suggests that capillary endothelial cells possess the potential to contribute to changes in luminal dimensions [10, 11, 12, 13, 14, 15]. Reorganisation of the endothelial microfilament system may be induced by many vasoactive chemicals [16, 17, 18]. Glyn and Ward [19]demonstrated focal narrowings in resin casts of capillaries and used phalloidin to prevent the changes of capillary dimensions which occur during reperfusion.…”

“…Glyn and Ward [19]demonstrated focal narrowings in resin casts of capillaries and used phalloidin to prevent the changes of capillary dimensions which occur during reperfusion. Phalloidin stabilises the contractile system by enhancing actin polymerisation [20, 21]but does not affect growth or metabolism [16, 17, 22]. The possibility of changes to the endothelial contractile cytoskeleton during conditions which induce narrowing of the capillary lumen [5]has not, however, been investigated.…”

Effect of phalloidin on structure and permeability of rete capillaries in the normal and hypoxic state.

“…We have reported that inhibition of energy metabolism and arrest of flow, followed by reperfusion, induces substantial structural and functional changes in the rete. 6 Other in vitro studies have suggested that reduced ATP generation results in restructuring and loss of actin filaments in endothelial cells. 14 -15 Therefore, normal and reperfused rete preparations were used in this study, with the idea that phalloidin might maintain the microvascular barrier through stabilization of cellular cytoskeletal micronlaments.…”

“…We have shown that this procedure combines the effects of arrest of both energy generation and flow. 6 Finally, the retia were reperfused with oxygenated control medium for 1 hour. The protocol was then repeated with six other retia in similar fashion, except that the perfusion medium throughout the experiment contained 10" 6 M phalloidin.…”