Morphometric analysis of gap junctions in regenerating arterial endothelium

Gap junctions may provide the structural basis for communication between arterial and endothelial cells and modulate their response to injury. We have utilized autoradiography and freeze fracture techniques to correlate proliferative activity with changes in the organization, density, and surface area of gap junctions in healing arterial endothelium. A well-circumscribed, reproducible area of endothelial loss was produced in the common carotid artery of the rabbit by desiccation of the intima. The lesion healed in 15 days by centripetal proliferation and migration of endothelial cells from adjacent uninjured areas. As controls, we used the uninjured contralateral artery. In parallel experiments, the vascular endothelium was sampled either for autoradiography after administration of 3H-thymidine or for freeze fracturing. Proliferative activity was measured by calculating the labeling index in autoradiographs of endothelium. The surface areas of gap junctions and that of the lateral endothelial membranes was measured by planimetry in electron micrographs of freeze fracture replicas. Two days after injury, cells at the growing edge of the endothelium revealed a marked decrease in the density and surface area of gap junctions, loss of tight junctions, and high labeling index (232 +/- 55 S.E.M.). At seven days, the labeling index was lower (61 +/- 31 S.E.M.), gap junctions were small but numerous, and short segments of tight junctions were present. At fifteen days, the endothelial integrity was restored, the labeling index was at control levels (3.32 +/- 3 S.E.M.), and both gap and tight junctions were well developed and indistinguishable from controls. The study shows that loss of junctions between endothelial cells is associated with high proliferative activity. As a corollary, well-developed gap junctions may prevent the response of the uninjured endothelium to circulating mitogens.