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Evidence that multiple P2X purinoceptors are functionally expressed in rat supraoptic neurones
Author(s) -
Shibuya Izumi,
Tanaka Keiko,
Hattori Yukio,
Uezono Yasuhito,
Harayama Nobuya,
Noguchi Jun,
Ueta Yoichi,
Izumi Futoshi,
Yamashita Hiroshi
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.351ae.x
Subject(s) - ppads , supraoptic nucleus , p2 receptor , purinergic receptor , suramin , agonist , extracellular , biology , adenosine triphosphate , antagonist , receptor , medicine , adenosine , in situ hybridization , endocrinology , microbiology and biotechnology , hypothalamus , biochemistry , gene expression , gene
1 The expression, distribution and function of P2X purinoceptors in the supraoptic nucleus (SON) were investigated by reverse transcription‐polymerase chain reaction (RT‐PCR), in situ hybridization, and Ca 2+ ‐imaging and whole‐cell patch‐clamp techniques, respectively. 2 RT‐PCR analysis of all seven known P2X receptor mRNAs in circular punches of the SON revealed that mRNAs for P2X 2 , P2X 3 , P2X 4 , P2X 6 and P2X 7 receptors were expressed in the SON, and mRNAs for P2X 3 , P2X 4 and P2X 7 were predominant. 3 In situ hybridization histochemistry for P2X 3 and P2X 4 receptor mRNAs showed that both mRNAs were expressed throughout the SON and in the paraventricular nucleus (PVN). 4 ATP caused an increase in [Ca 2+ ] i in a dose‐dependent manner with an ED 50 of 1.7 × 10 −5 m . The effects of ATP were mimicked by ATPγS and 2‐methylthio ATP (2MeSATP), but not by AMP, adenosine, UTP or UDP. αβ‐Methylene ATP (αβMeATP) and ADP caused a small increase in [Ca 2+ ] i in a subset of SON neurones. 5 The P2X 7 agonist 2′‐ & 3′‐O‐(4‐benzoylbenzoyl)‐ATP (BzATP) at 10 −4 m increased [Ca 2+ ] i , but the potency of BzATP was lower than that of ATP. In contrast, BzATP caused a more prominent [Ca 2+ ] i increase than ATP in non‐neuronal cells in the SON. 6 The effects of ATP were abolished by extracellular Ca 2+ removal or by the P2 antagonist pyridoxal phosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS), and inhibited by extracellular Na + replacement or another P2 antagonist, suramin, but were unaffected by the P2X 7 antagonist oxidized ATP, and the inhibitor of Ca 2+ ‐ATPase in intracellular Ca 2+ stores cyclopiazonic acid. 7 Two patterns of desensitization were observed in the [Ca 2+ ] i response to repeated applications of ATP: some neurones showed little or moderate desensitization, while others showed strong desensitization. 8 Whole‐cell patch‐clamp analysis showed that ATP induced cationic currents with marked inward rectification. The ATP‐induced currents exhibited two patterns of desensitization similar to those observed in the [Ca 2+ ] i response. 9 The results suggest that multiple P2X receptors, including P2X 3 , are functionally expressed in SON neurones, and that activation of these receptors induces cationic currents and Ca 2+ entry. Such ionic and Ca 2+ ‐signalling mechanisms triggered by ATP may play an important role in the regulation of SON neurosecretory cells.