A characterization of pervanadate, an inducer of cellular tyrosine phosphorylation and inhibitor of gap junctional intercellular communication

Gap junctional intercellular communication (GJIC), phosphorylation status of the gap junction protein, connexin43 (Cx43), and cellular tyrosine phosphorylation in Syrian hamster embryo cells have been employed for a biological characterization of pervanadate (a mixture of H2O2 and vanadate). In addition, electron paramagnetic resonance (EPR) spectroscopy was used to follow the appearance and disappearance of vanadyl (V(IV)). It has previously been suggested that pervanadate is vanadyl hydroperoxide (V(4+)OOH). This assumption was tested by using mixtures with different molar ratios of H2O2 and orthovanadate, metavanadate or vanadyl sulfate. The maximal biological activity of the mixtures were found at a molar ratio of 2:1 (H2O2:orthovanadate or metavanadate) or 2.5:1 (H2O2:alkaline vanadyl sulfate). No V(IV) EPR spectrum appeared upon mixing orthovanadate or metavanadate and H2O2. The V(IV) EPR spectrum disappeared when vanadyl sulfate was incubated with H2O2 in a 0.5:1 molar ratio (H2O2:alkaline vanadyl sulfate). Spectrophotometrically, a V(V)-like peak at 265 nm had its optimum at this ratio. These results are consistent with pervanadate being diperoxovanadate. The individual compounds were prominently less active than the per-compound mixtures in affecting the biological parameters. The decreases in GJIC showed a concentration-dependent correlation with the onset of the alterations of the Cx43 band pattern and the amount of phosphotyrosine in cellular proteins, but the correlation was not absolute. All the studied biological parameters were reversible, also under continuous exposure to pervanadate.