The role of extracellular matrix of retinal pigment epithelial cells (RPE-ECM) in the regulation of the survival of choriocapillaris endothelial cells (CCE) was investigated in vitro. The CCE survival was evaluated by trypan blue staining, neutral red uptake, and the counting of viable cells. Results showed that CCE cells survived on RPE-ECM. Pre-treatment of RPE-ECM individually with neutralizing antibodies to acidic fibroblast growth factor, vascular endothelial growth factor, platelet-derived growth factor, or transforming growth factor beta(pan specific to TGFbeta1, TGFbeta1.2, TGFbeta2 and TGFbeta5), did not alter the survival rate of CCE cells on RPE-ECM, as compared to that of the control (CCE survival rates on RPE-ECM pretreated with normal rabbit IgG). However, the treatment of RPE-ECM with neutralizing antibody to basic fibroblast growth factor (bFGF) caused CCE death by 77.1+/-15.7%. The CCE death was defined as apoptosis based on the morphological markers (shrinkage in cell size with blebbing of plasma membranes, condensation and fragmentation of nuclei, and DNA fragmentation in multiples of approximately 200 bp). The addition of phorbol 12-myristate 13-acetate (PMA) (2 nM) to the culture medium was effective for complete prevention of CCE apoptosis; the protecting effect of PMA on CCE apoptosis can be abolished by H7 (25 microM), but not HA1004 (50 microM), suggesting the involvement of PKC in protecting CCE from apoptosis. The inhibition of protein synthesis of CCE cells by cycloheximide (0.1 microM) did not affect the apoptotic process of the cells. In a separate experiment, when CCE cells were cultured in a medium saturated with bFGF (5 ng ml-1) without RPE-ECM, the cells also died by apoptosis. However, this apoptotic process was not affected by PMA. Cycloheximide also failed to affect the apoptotic process. These results suggest that both RPE-ECM insoluble molecules and RPE-ECM-bound bFGF modulate choriocapillaris survival by suppressing CCE apoptosis.