Low dose of bradykinin selectively increases intracellular calcium in glioma cells

To investigate the underlying basis for the selective modulation of the permeability of the blood-brain barrier by small doses of bradykinin, we first established cell lines of rat brain microvascular endothelial cells (BMECs) and astrocytes by primary cultures from neonatal rats. BMECs, astrocytes and C6 glioma cells were treated with different concentrations of BK (range from 10- 8 M to 10- 4 M), and changes of intracellular calcium levels were measured by fluorescence spectrophotometry. Expression levels of B2 receptors were analyzed by Western blot analysis. We found that a low dose (10- 6 M) of BK could trigger an elevation of intracellular calcium level in C6 glioma cells, whereas astrocytes responded to a higher concentration of BK (10- 5 M), and the BMECs remained unresponsive to BK. Western blot results showed that C6 glioma cells expressed the highest level of B2 receptors compared with primary astrocytes or BMECs. B2 receptors are highly expressed in glioma cells and a low dose of BK selectively increases the intracellular calcium level in tumor cells which, in turn, could contribute to the selective increase in the permeability of the blood-tumor barrier by small doses of BK.