Water channels in platelet volume regulation

The regulation of platelet volume significantly affects its function. Because water is the major molecule in cells and its active transport via water channels called aquaporins (AQPs) have been implicated in cellular and organelle volume regulation, the presence of water channels in platelets and their potential role in platelet volume regulation was investigated. G-protein–mediated AQP regulation in secretory vesicle swelling has previously been reported in neurons and in pancreatic acinar cells. Mercuric chloride has been demonstrated to inhibit most AQPs except AQP6, which is stimulated by the compound. Exposure of platelets to HgCl(2)-induced swelling in a dose-dependent manner, suggesting the presence of AQP6 in platelets. Immunoblot analysis of platelet protein confirmed the presence of AQP6, and also of G(αo), G(αi–1) and G(αi–3) proteins. Results from this study demonstrate for the first time that in platelets AQP6 is involved in cell volume regulation via a G-protein–mediated pathway.