Intracellular ATP modulates vascular distinctive P2X receptors in rat arterial smooth muscle

Abstract

The extracellular nucleotide sensitive P2 receptor comprises two different groups: ionotropic P2X and metabotropic P2Y receptors. It is generally considered that the P2X receptor lacks intracellular ATP binding sites.In rat arterial myocytes, however, we identified that P2X1 and 5 receptors form a heteromultimer and found that its activation kinetics is modulated by cytosolic ATP, since a significant decrease was observed in desensitization of P2X receptor current evoked by repeated application of α,β‐methylene ATP (10μM) at 5 minute intervals with increasing intracellular ATP concentration (0, 2 and 5mM to 52.4±6.0%, 45.7±5.4% and 33.5±3.0%, respectively: n=5–13). In contrast, ADP and AMP did not modulate the current. Similar effects were observed in rat cerebral and mesenteric artery myocytes.Therefore, we performed a homology search for ATP‐binding motifs in P2X receptors, and found P2X1 and 5 receptors have the motifs at the pore‐forming transmembrane regions. In addition, we confirmed the co‐localization of P2X1 and 5 receptor proteins in each arterial tissue by RT‐PCR, western blot and immunostaining analyses.These results suggest that P2X1 and 5 receptors may play important roles in metabolic regulation in conditions such as hypoxia.