Abstract
We recently reported that a novel hetero-oligomeric P2X receptor is formed from the P2X1 and P2X5 isoforms when coexpressed in human embryonic kidney 293 cells (Torres et al., 1998). A more complete description of the pharmacology of this novel receptor is presented here. A brief application of ATP to a voltage-clamped cell transiently expressing P2X1/5 receptors resulted in a biphasic current that rapidly reached a peak and then decayed to a sustained plateau. Washout of ATP was accompanied by generation and fade of a pronounced tail of inward current. EC50 values were determined from concentration-response curves for a range of agonists. The rank order of agonist potency was ATP ≥ 2 methylthio ATP > adenosine 5′-O-(3-thiotriphosphate) > α,β-methylene ATP > ADP > CTP. α,β-methylene ADP, UTP, GTP, and AMP were ineffective. Only ATP and 2 methylthio ATP were full agonists. IC50 values were determined from concentration-response curves for three commonly used purinergic antagonists. Suramin and pyridoxal phosphate-6-azophenyl-2′, 4′-disulfonic acid were equipotent at P2X1 and P2X1/5 receptors; however, the P2X1/5 receptor was much less sensitive to TNP-ATP than was the P2X1 receptor. The amplitude of peak ATP-gated current was relatively insensitive to changes in [Ca2+]O (1–30 mM). Finally, plateau currents were potentiated by low concentrations of pyridoxal phosphate-6-azophenyl-2′, 4′-disulfonic acid and by raising [Ca2+]O. These results provide additional information on the pharmacological profile of the recombinant P2X1/5 receptor channel and provide a basis to further evaluate ATP-induced currents in native tissues.
Footnotes
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Send reprint requests to: Dr. William R. Haines, Department of Pharmacological and Physiological Science, St. Louis University School of Medicine, 1402 S. Grand Blvd., St. Louis, MO 63104. E-mail:haineswr{at}slu.edu
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This work was supported by National Institutes of Health Grants HL56236 (T.M.E.) and NS35534 (M.M.V.) and an American Heart Association Missouri Affiliate Predoctoral Fellowship 9804090X (W.R.H).
- Abbreviations:
- PPADS
- pyridoxal phosphate-6-azophenyl-2′,4′-disulfonic acid
- α,β-meADP, α,β-methylene ADP
- α,β-meATP,α,β-methylene ATP
- ATPγS
- adenosine 5′-O-(3-thiotriphosphate)
- TNP-ATP
- 2′,3′-O-(2,4,6-trinitrophenyl) ATP
- 2-meSATP
- 2-methylthio ATP
- HEK
- human embryonic kidney
- Received April 21, 1999.
- Accepted July 2, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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