Glioma cells induce gamma-glutamyl transpeptidase activity in cultured blood but not lymphatic endothelial cells.

Glial cells have been shown to induce enzyme activities, which are characteristically high in brain capillaries, in cerebral and non cerebral endothelial cells in culture. We evaluated the activity of gamma-glutamyl transpeptidase (gamma GT) in freshly isolated (ex vivo) bovine blood (BEC) and lymphatic (LEC) endothelial cells. We also tested the effect of C6 glioma cell conditioned medium (GCM) on gamma GT activity of BEC and LEC in primary culture. Ex vivo BEC had a high gamma GT activity, only 9% of which was retained in culture. After exposure to GCM, however, gamma GT activity of cultured BEC was twofold higher than with control medium. By contrast gamma GT activity was extremely low in ex vivo LEC and did not significantly increase in cultured LEC exposed to GCM. These data show that the basal levels of gamma GT are markedly different in BEC and LEC and also that, unlike BEC, LEC are not capable of producing more gamma GT in response to glial stimulation.