Rho kinase-mediated reduction in cardiac capillary endothelial cell dimensions, in situ, against flow

Objective: We previously showed that ischemia, induced by interrupting vascular Row, reduced cardiac capillary caliber. This was accomplished by a reduction in endothelial cell dimensions which was sensitive to Rho kinase (ROK) inhibition and stabilization of the actin cytoskeleton. Here, we investigated whether similar changes in endothelial cells, in situ, could be elicited in the presence of flow through the capillary bed. Methods: Langendorffs perfused rat: hearts were subjected to vasoactive agents., ischemia, and reperfusion. Luminal and abluminal perimeters of capillary cross-sections and their areas were measured from electron micrographs to monitor changes in endothelial cell dimensions. Results: Histamine (100 AM) reduced capillary endothelial cell dimensions., in situ, without endothelial injury While cross-sectional areas of endothelial cells were not altered by histamine, all other parameters measured were significantly reduced in comparison to controls. These changes were prevented by ROK inhibition. Conclusions: Cardiac capillary endothelial cells, in situ, are able to change shape against continuous flow. One hundred (100) AM histamine induces morphometric changes in these endothelial cells, in. situ, without cell damage. These cell-shape changes require ROK and mimic those observed following Invocardial ischemia. Targeting the actomyosin contractile system may be useful in ameliorating effects of ischemia on the myocardium.