Studies on corneal endothelial growth and repair. II. Increased transcription as detected by incorporation of H-uridine and H-actinomycin D

Endothelial cells from injured frog corneas undergo increased ³H-uridine and ³H-actinomycin D (³H-AMD) incorporation as judged by autoradiography. The increase in ³H-AMD binding occurs when living endothelium is labeled in vitro or when fixed preparations are exposed to the drug. The changes in ³H-AMD incorporation detected by the two methods are comparable (55 and 62 % for living and pre-fixed tissue respectively). However, when fixed endothelium is also de-histonized with 2 N HCl, differential binding of ³H-AMD is eliminated. This result suggests that the enhanced incorporation of ³H-AMD into nuclei is at least partly due to a modification in the association of chromosomal proteins with DNA and not entirely to cell permeability changes that may accompany wound repair. This contrasts with observations of cells that are killed outright by the injury. Such cells bind very large amounts of ³H-AMD compared with their living neighbors. Here the difference in incorporation is eliminated by prefixation. Thus, in the dead cells increased binding may be due to a reduction of cell surface permeability barriers which accompanies cell morbidity.