USE OF RHODAMINE-123 TO EXAMINE THE FUNCTIONAL-ACTIVITY OF P-GLYCOPROTEIN IN PRIMARY CULTURED BRAIN MICROVESSEL ENDOTHELIAL-CELL MONOLAYERS

The fluorescent dye, rhodamine 123, was used to evaluate the functiona l activity of the P-glycoprotein (P-gp) efflux transport system in pri mary cultured bovine brain microvessel endothelial cell (BBMEC) monola yers. Rhodamine 123 accumulation was increased significantly in BBMEC monolayers treated with the P-gp modifying agent, cyclosporin A (CSA). Rhodamine 123 accumulation was also increased by other P-gp modifying agents. The rank effectiveness of these agents in increasing rhodamin e 123 accumulation in BBMEC monolayers was CSA=dipyridamole>verapamil= quinidine. The maximal increase in rhodamine 123 accumulation in CSA t reated BBMEC monolayers was approximately 3 fold greater than in contr ol monolayers and was qualitatively similar to that observed with 3H-v incristine. Comparison of functional activity with the biochemical exp ression of P-gp in BBMEC monolayers and in an established tumor cell l ine that over-expresses P-gp indicate that functional activity may be a more descriptive measure of the importance of this drug efflux syste m than protein expression. Furthermore, these studies suggest that acc umulation of rhodamine 123 in BBMEC monolayers can be used to quantita tively examine P-gp activity in the blood-brain barrier.