Preliminary characterization of glial-secreted factors responsible for the induction of high electrical resistances across endothelial monolayers in a blood-brain barrier model.

Factors secreted by C6 glioma cells which induce electrical resistances across endothelial monolayers in an in vitro blood-brain barrier model have been partially characterised for the first time. These transendothelial electrical resistances (TEERs) were only evident when cell-free conditioned medium derived from C6 glioma cells was applied to the basolateral surfaces of confluent ECV304 or ECV304-9 cells which are both human umbilical vein endothelial cell lines (HUVEC). Electrical resistance values as high as 600 ohm. sq cm were obtained with this blood-brain barrier model and ultrafiltration techniques suggest that any factor(s) in the conditioned medium responsible for these TEERs have molecular masses of less than 1000 Da. Enzymic proteolysis and heat treatment carried out on the conditioned medium failed to inhibit its effect on the HUVEC monolayers suggesting that these C6 cell-secreted factors are unlikely to be proteins.