Functional expression of V-ATPases in the plasma membrane of glial cells

Vacuolar H(+) ATPase (V-ATPase) activity is essential for many cellular processes, including intracellular membrane traffic, protein processing and degradation, and receptor-mediated endocytosis. Proton transport by V-ATPases could also play a role during cell transformation, tumorigenesis, and cell metastasis, and V-ATPase c-subunit overexpression was reported to be correlated with invasiveness of pancreatic tumors (Ohta et al., 1996). In the present work, we found that mRNAs encoding V-ATPase subunits are not overexpressed in C6 tumoral glioma cells when compared with immortalized astrocytes DI TNC1 and astrocytes in primary cultures. Accordingly, V-ATPase subunit mRNA levels are similar in human gliomas (grade II or IV) and in peritumoral tissues. A significant proportion (25%) of V-ATPase is present in the plasma membrane of both the C6 and the DI TNC1 astrocytic cells in culture. A bafilomycin-sensitive hyperpolarizing pump current through the plasma membrane was detected and measured after ionic channel inhibition, which corresponds most probably to an electrogenic transport of protons. This suggests that the plasma membrane V-ATPase is active. It could contribute to cytoplasmic pH regulation in astrocytic cells.