RT Journal Article
SR Electronic
T1 ATP, an Agonist at the Rat P2Y<sub>4</sub> Receptor, Is an Antagonist at the Human P2Y<sub>4</sub> Receptor
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 926
OP 931
VO 57
IS 5
A1 Charles Kennedy
A1 Ai-Dong Qi
A1 Christopher L. Herold
A1 T. Kendall Harden
A1 Robert A. Nicholas
YR 2000
UL http://molpharm.aspetjournals.org/content/57/5/926.abstract
AB The nucleotide selectivities of the human P2Y4(hP2Y4) and rat P2Y4 (rP2Y4) receptor stably expressed in 1321N1 human astrocytoma cells were determined by measuring increases in intracellular [Ca2+] under conditions that minimized metabolism, bioconversion, and endogenous nucleotide release. In cells expressing the hP2Y4 receptor, UTP, GTP, and ITP all increased intracellular [Ca2+] with a rank order of potency of UTP (0.55) &gt; GTP (6.59) = ITP (7.38), (EC50, μM). ATP, CTP, xanthine 5′-triphosphate (XTP), and diadenosine 5′,5‴-P1,P4-tetraphosphate (Ap4A), all at 100 μM, were inactive at the hP2Y4 receptor. In cells expressing the rP2Y4receptor, all seven nucleotides increased intracellular [Ca2+] with similar maximal effects and a rank order of potency of UTP (0.20) &gt; ATP (0.51) &gt; Ap4A (1.24) ≈ ITP (1.82) ≈ GTP (2.28) &gt; CTP (7.24) &gt; XTP (22.9). Because ATP is inactive at the hP2Y4 receptor, we assessed whether ATP displayed antagonist activity. When coapplied, ATP shifted the concentration-response curve to UTP rightward in a concentration-dependent manner, with no change in the maximal response. A Schild plot derived from these data gave a pA2 value of 6.15 (KB = 708 nM) and a slope near unity. Additionally, CTP and Ap4A (each at 100 μM) inhibited the response to an EC50 concentration of UTP by ∼40 and ∼50%, respectively, whereas XTP had no effect. The inhibitory effects of ATP, CTP, and Ap4A were reversible on washout. Thus, ATP is a potent agonist at the rP2Y4receptor but is a competitive antagonist with moderate potency at the hP2Y4 receptor. The American Society for Pharmacology and Experimental Therapeutics