Neelands Torben R, Burgard Edward C, Uchic Marie E, McDonald Heath A, Niforatos Wende, Faltynek Connie R, Lynch Kevin J, Jarvis Michael F
Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, R04PM, AP9A, Abbott Park, IL 60064-6123, USA.
Br J Pharmacol. 2003 Sep;140(1):202-10. doi: 10.1038/sj.bjp.0705411. Epub 2003 Jul 29.
(1) Rapid desensitization of ligand-gated ion channel receptors can alter the apparent activity of receptor modulators, as well as make detection of fast-channel activation difficult. Investigation of the antagonist pharmacology of ATP-sensitive homomeric P2X3 receptors is limited by agonist-evoked fast-desensitization kinetics. (2) In the present studies, chimeric receptors were created using the coding sequence for the N-terminus and the first transmembrane domain of either the nondesensitizing human P2X2a or fast-desensitizing P2X3 receptor joined to the sequence encoding the extracellular loop, second transmembrane domain, and C-terminus of the other receptor (designated P2X2-3 and P2X3-2, respectively). These clones were stably transfected into 1321N1 astrocytoma cells for biophysical and pharmacological experiments using both electrophysiological and calcium-imaging methods. (3) Chimeric P2X2-3 and P2X3-2 receptors were inwardly rectifying and agonist responses showed desensitization properties similar to the wild-type human P2X2a and P2X3 receptors, respectively. (4) The P2X2-3 chimera displayed an agonist pharmacological profile similar to the P2X3 wild-type receptor being activated by low concentrations of both ATP and alpha,beta-meATP. In contrast, the P2X3-2 chimera had markedly reduced sensitivity to both agonists. (5) The P2X3 receptor antagonists TNP-ATP and A-317491 were shown to be potent, competitive antagonists of the P2X2-3 chimera (Ki=2.2 and 52.1 nm, respectively), supporting the hypothesis that rapid receptor desensitization can mask the competitive antagonism of wild-type homomeric P2X3 receptors.
(1) 配体门控离子通道受体的快速脱敏可改变受体调节剂的表观活性，同时也会使快速通道激活的检测变得困难。对ATP敏感的同聚体P2X3受体的拮抗剂药理学研究受到激动剂诱发的快速脱敏动力学的限制。(2) 在本研究中，通过将不脱敏的人P2X2a或快速脱敏的P2X3受体的N端和第一个跨膜结构域的编码序列与另一个受体的细胞外环、第二个跨膜结构域和C端的编码序列连接，构建了嵌合受体（分别命名为P2X2-3和P2X3-2）。这些克隆被稳定转染到1321N1星形细胞瘤细胞中，使用电生理和钙成像方法进行生物物理和药理学实验。(3) 嵌合P2X2-3和P2X3-2受体呈内向整流，激动剂反应分别表现出与野生型人P2X2a和P2X3受体相似的脱敏特性。(4) P2X2-3嵌合体显示出与P2X3野生型受体相似的激动剂药理学特征，可被低浓度的ATP和α,β-甲硫腺苷三磷酸（α,β-meATP）激活。相比之下，P2X3-2嵌合体对这两种激动剂的敏感性明显降低。(5) P2X3受体拮抗剂TNP-ATP和A-317491被证明是P2X2-3嵌合体的有效竞争性拮抗剂（Ki分别为2.2和52.1 nM），支持了快速受体脱敏可掩盖野生型同聚体P2X3受体竞争性拮抗作用的假说。
