Increased permeability is an early and universal response of the vasculature to radiation injury, yet the biological basis of this reaction is poorly understood. The present study determined the time course and the dose-response relationship of radiation-induced hyperpermeability in cultured bovine pulmonary artery endothelial (BPAE) cells. BPAE cells were grown to a confluent monolayer on microcarrier beads, and column chromatography methods were used to evaluate permeability to two low molecular weight compounds: sodium fluorescein (NaFlsc, mol. wt. = 342) and cyanocobalamin (B12, mol. wt. = 1355). This is a novel in vitro model to study mechanisms and modifiers of radiation-induced permeability of endothelial cells under flow conditions using nonradioactive tracers. Cell-covered beads were exposed to a single dose of 10 Gy Of 137Cs gamma rays and placed in the column, and permeability was measured every 30 min for 3 h. There was a time-dependent increase in permeability to both tracers, reaching significance by 2 h. Increased permeability was accompanied by perturbations in F-actin distribution in the BPAE cells as determined by rhodamine-phalloidin fluorescence microscopy. Neither catalase nor captopril ameliorated this hyperpermeability, but dibutyryl cAMP partially prevented it. At 3 h after 0, 1, 2, 5 and 10 Gy irradiation, permeability values of 11.8 +/- 2.1, 13.9 +/- 2.2, 20.9 +/- 3.6, 24.8 +/- 2.8 and 27.2 +/- 3.3 (10(-5) cm/s, +/- SEM), respectively, were observed using NaFlsc. The increase was significant (P < 0.05) at 2 Gy or higher. Permeability to B12 was significantly elevated after 5 or 10 Gy. These results suggest that permeability of endothelial cells to low molecular weight solutes increases within 3 h after therapeutic doses of radiation, and that cAMP ameliorates this response.