Unveiling the agonistic properties of Preyssler-type Polyoxotungstates on purinergic P2 receptors.

The Preyssler-type polyoxotungstate ({PW}) belongs to the family of polyanionic metal-oxides formed by group V and VI metal ions, such as V, Mo and W, commonly known as polyoxometalates (POMs). POMs have demonstrated inhibitory effect on a significant number of ATP-binding proteins in vitro. Purinergic P2 receptors, widely expressed in eukaryotic cells, contain extracellularly oriented ATP-binding sites and play many biological roles with health implications. In this work, we use the immortalized mouse hippocampal neuronal HT-22 cells in culture to study the effects of {PW} on the cytosolic Ca concentration. Changes in cytosolic Ca concentration were monitored using fluorescence microscopy of HT-22 cells loaded with the fluorescent Ca indicator Fluo3. P-Nuclear magnetic resonance measurements of {PW} indicate its stability in the medium used for cytosolic Ca measurements for over 30 min. The findings reveal that addition of {PW} to the extracellular medium induces a sustained increase of the cytosolic Ca concentration within minutes. This Ca increase is triggered by extracellular Ca entry into the cells and is dose-dependent, with a half-of-effect concentration of 0.25 ± 0.05 μM {PW}. In addition, after the {PW}-induced cytosolic Ca increase, the transient Ca peak induced by extracellular ATP is reduced up to 100% with an apparent half-of-effect concentration of 0.15 ± 0.05 μM {PW}. Activation of metabotropic purinergic P2 receptors affords about 80% contribution to the increase of Fluo3 fluorescence elicited by {PW} in HT-22 cells, whereas ionotropic receptors contribute, at most, with 20%. These results suggest that {PW} could serve as a novel agonist of purinergic P2 receptors.