リガンドや流れ刺激により誘導されるP2X4チャネルの細胞膜への移行

抄録

Purinergic P2X4 receptor is a non-selective ATP-gated channel, and is distributed in various tissues including vascular endothelial cells (ECs). Our previous studies demonstrated that P2X4 in ECs mediates flow-induced Ca²⁺ influx and subsequent NO production, and regulates vascular remodeling. Our fluorescence microscopic observation showed that P2X4 channels are predominantly localized on the intracellular vesicles, and that a very small fraction is present at the cell surface where P2X4s should sense extracellular ATP. The mechanisms involved in the up-regulation of cell surface P2X4 remains unclear. To address this issue, we investigated the intracellular dynamics of P2X4 during sensing stimulus. We found that ligand treatment or flow shear stress increased the amount of channels biotinylated by membrane-impermeable reagents, namely P2X4 at the cell surface, by a factor of 1.5–2. Consistently, we observed massive Ca²⁺-dependent exocytosis of GFP-tagged P2X4 on the plasma membrane in response to ligand treatment or shear stress using total internal reflection fluorescence microscopy. Furthermore P2X4 currents evoked by ATP were increased after a second repetitive ligand treatment. These results suggest that the number of cell surface P2X4 of ECs is up-regulated by shear stress, leading to an apparent increase in the sensitivity to external ATP. [J Physiol Sci. 2008;58 Suppl:S84]