title: Purinergic P2X(2) receptor desensitization depends on coupling between ectodomain and C-terminal domain.
abstract: The wild-type P2X(2) purinergic receptor (P2X(2a)R) and its splice form lacking the intracellular Val(370)-Gln(438) C-terminal sequence (P2X(2b)R) respond to ATP stimulation with comparable EC(50) values and peak current/calcium responses but desensitize in a receptor-specific manner. P2X(2a)R desensitizes slowly and P2X(2b)R desensitizes rapidly. We studied the effects of different agonists, and of substituting the ectodomain, on the pattern of calcium signaling by P2X(2a)R and P2X(2b)R. Both receptors showed similar EC(50) values (estimated from the peak calcium response) and IC(50) values (estimated from the rate of calcium signal desensitization) for agonists, in the order 2-MeS-ATP <or= ATP <or= ATPgammaS < BzATP << alphabeta-meATP, and the IC(50) values for agonists were shifted to the right compared with their EC(50) values. Furthermore, the ATP-induced receptor-subtype specific pattern of desensitization was mimicked by high- but not by low-efficacy agonists, suggesting a ligand-specific desensitization pattern. To test this hypothesis, we generated chimeric P2X(2a)R and P2X(2b)R containing the Val(60)-Phe(301) ectodomain sequence of P2X(3)R and Val(61)-Phe(313) ectodomain sequence of P2X(7)R instead the native Ile(66)-Tyr(310) sequence. The mutated P2X(2a)+X(3)R and P2X(2b)+X(3)R exhibited comparable EC(50) values for ATP, BzATP, and alphabeta-meATP in the submicromolar concentration range and desensitized in a receptor-specific and ligand-nonspecific manner. On the other hand, the chimeric P2X(2)+X(7)R exhibited decreased sensitivity for ATP and desensitized in a receptor-nonspecific manner. These results suggest that efficacy of agonists for the ligand-binding domain of P2X(2)Rs reflects the strength of desensitization controlled by their C-terminal structures.
authors.affiliation: Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510, USA.
authors.forename: Mu-Lan
authors.initials: ML
authors.lastname: He
authors.forename: Taka-Aki
authors.initials: TA
authors.lastname: Koshimizu
authors.forename: Melanija
authors.initials: M
authors.lastname: Tomić
authors.forename: Stanko S
authors.initials: SS
authors.lastname: Stojilkovic
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D051379:Mice; D017434:Protein Structure, Tertiary; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2 / Q000737:chemistry; D058476:Receptors, Purinergic P2X2; D014162:Transfection
chemical_list: C546401:P2RX2 protein, human; C546402:P2rx2 protein, mouse; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2; D058476:Receptors, Purinergic P2X2; D000255:Adenosine Triphosphate; D002118:Calcium