The actions of an intracellular
nitric oxide generator compound on the properties of a co-culture model of the blood-brain barrier are described. Addition of the
iron-sulphur cluster nitrosyl
Roussin's black salt (RBS, heptanitrosyl-tri-mu3-thioxotetraferrate (1-)) resulted in a rapid and dose-dependent (50-250 microM) decline in the electrical resistance displayed by co-cultures of vascular endothelial cells and C6
glioma cells. The breach in barrier integrity elicited by RBS (250 microM) could be prevented by either haemoglobin (100 microM),
methylene blue (200 microM), or by photon-induced inactivation of RBS. In contrast, the
nitric oxide synthase inhibitor nitro-
L-arginine methyl ester (250 microM) caused no inhibition in the decline in resistance of RBS-exposed cultures. Addition of 8-bromo-guanosine-cyclic monophosphate (500 microM) did not mimic the actions of RBS. Exposure to intense light of co-cultures manifesting a high transcellular electrical resistance resulted in a reduction in tissue resistance which could be prevented by the presence of haemoglobin (100 microM). We conclude that
nitric oxide liberated from RBS results in a reversible diminution in the integrity of the endothelial cell barrier in the co-culture system, and we suggest that light-sensitive endogenous
nitric oxide generator compounds may be present in intact cells. Possible roles of
nitric oxide in blood-brain-barrier function are considered.