title: ATP, an agonist at the rat P2Y(4) receptor, is an antagonist at the human P2Y(4) receptor.
abstract: The nucleotide selectivities of the human P2Y(4) (hP2Y(4)) and rat P2Y(4) (rP2Y(4)) receptor stably expressed in 1321N1 human astrocytoma cells were determined by measuring increases in intracellular [Ca(2+)] under conditions that minimized metabolism, bioconversion, and endogenous nucleotide release. In cells expressing the hP2Y(4) receptor, UTP, GTP, and ITP all increased intracellular [Ca(2+)] with a rank order of potency of UTP (0.55) > GTP (6.59) = ITP (7.38), (EC(50), microM). ATP, CTP, xanthine 5'-triphosphate (XTP), and diadenosine 5',5"'-P(1), P(4)-tetraphosphate (Ap(4)A), all at 100 microM, were inactive at the hP2Y(4) receptor. In cells expressing the rP2Y(4) receptor, all seven nucleotides increased intracellular [Ca(2+)] with similar maximal effects and a rank order of potency of UTP (0.20) > ATP (0. 51) > Ap(4)A (1.24) approximately ITP (1.82) approximately GTP (2. 28) > CTP (7.24) > XTP (22.9). Because ATP is inactive at the hP2Y(4) 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 pA(2) value of 6.15 (K(B) = 708 nM) and a slope near unity. Additionally, CTP and Ap(4)A (each at 100 microM) inhibited the response to an EC(50) concentration of UTP by approximately 40 and approximately 50%, respectively, whereas XTP had no effect. The inhibitory effects of ATP, CTP, and Ap(4)A were reversible on washout. Thus, ATP is a potent agonist at the rP2Y(4) receptor but is a competitive antagonist with moderate potency at the hP2Y(4) receptor.
authors.affiliation: Department of Physiology and Pharmacology, University of Strathclyde, Glasgow, Great Britain.
authors.forename: C
authors.initials: C
authors.lastname: Kennedy
authors.forename: A D
authors.initials: AD
authors.lastname: Qi
authors.forename: C L
authors.initials: CL
authors.lastname: Herold
authors.forename: T K
authors.initials: TK
authors.lastname: Harden
authors.forename: R A
authors.initials: RA
authors.lastname: Nicholas
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D015226:Dinucleoside Phosphates / Q000494:pharmacology; D006801:Humans; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D013045:Species Specificity; D014407:Tumor Cells, Cultured; D014530:Uridine Diphosphate / Q000494:pharmacology
chemical_list: D015226:Dinucleoside Phosphates; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; C104749:purinoceptor P2Y4; C020733:diadenosine tetraphosphate; D014530:Uridine Diphosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate