Vanadate inhibition of rat cerebral cortex Na+,K+-ATPase during postnatal development

Tetra-quinolinium ditelluro(VI)octa-vanadate(V) octa-hydrate

In the title compound, (C₉H₈N)₄[Te₂V₈O₂₈]·8H₂O, the com­plete heteropolyanion is generated by a crystallographic inversion centre. One of the two quniolinium ions forms an N—H⋯O_p (p = polyoxidometallate) hydrogen bond and the other an N—H⋯O_w (w = water) hydrogen bond. The water mol­ecules further link the components by O—H⋯O_p and O—H⋯O_w hydrogen bonds. A number of C—H⋯O inter­actions and aromatic π–π stacking inter­actions [shortest centroid–centroid separation = 3.541 (7) Å] are also observed. Together, these generate a three-dimensional network.

Na+, K+-ATPase activity in cultured C6 glioma cells

Rat C6 glioma cells were cultured for 4 days in MEM medium supplemented with 10% bovine serum and Na+, K+-ATPase activity was determined in homogenates of harvested cells. Approximately 50% of enzyme activity was attained at 1.5 mM K+ and the maximum (2.76 +/- 0.13 mumol Pi/h/mg protein) at 5 mM K+. The specific activity of Na+, K+-ATPase was not influenced by freezing the homogenates or cell suspensions before the enzyme assay. Ten minutes' exposure of glioma cells to 10(-4) or 10(-5) M noradrenaline (NA) remained without any effect on NA+, K+-ATPase activity. Neither did the presence of NA in the incubation medium, during the enzyme assay, influence the enzyme activity. The nonresponsiveness of Na+, K+-ATPase of C6 glioma cells to NA is consistent with the assumption that alpha (+) form of the enzyme may be preferentially sensitive to noradrenaline. Na+, K+-ATPase was inhibited in a dose-dependent manner by vanadate and 50% inhibition was achieved at 2 x 10(-7) M concentration. In spite of the fact that Na+, K+-ATPase of glioma cells was not responsive to NA, the latter could at least partially reverse vanadate-induced inhibition of the enzyme. Although the present results concern transformed glial cells, they suggest the possibility that inhibition of glial Na+, K+-ATPase may contribute to the previously reported inhibition by vanadate of Na+, K+-ATPase of the whole brain tissue.