Abstract
We have reported that externally applied ATP induces non selective cation currents in pregnant rat myometrial cells and suggested the currents contribute to spontaneous depolarization leading to uterine contraction (Pflügers Arch. 447, 457-64, 2004). However, the channel that carries the ATP sensitive non selective cation currents have not been molecularly identified in rat uterus. Thus, expression of P2X receptor in mRNA levels was screened with RT-PCR method using cDNA library from pregnant rat myometrium at day 21. Most abundantly expressed P2X4 (more than 99% sequence homology to that of rat brain) among other subtypes (P2X1 through P2X7) was cloned, and functionally expressed in COS-7 or CHO cells. The expressed channels were activated by externally applied ATP as well as other nucleotides (ATP>GTP>UTP>ADP). The activated channels were non selectively permeable to various monovalent cations (K+>Cs+>Na+>Li+) and were blocked by non selective P2 receptor antagonist, suramin and selective P2X blocker, PPADS. These properties resembles to those of ATP sensitive non selective cation currents previously reported in pregnant rat uterus. These results, therefore, indicate that P2X4 receptor is the most probable candidate for carrying the ATP sensitive non selective cation currents in pregnant rat myometrium. [Jpn J Physiol 54 Suppl:S123 (2004)]
