Gerevich Zoltan, Zadori Zoltan S, Köles Laszlo, Kopp Laurenz, Milius Doreen, Wirkner Kerstin, Gyires Klara, Illes Peter
Rudolf-Boehm-Institute of Pharmacology and Toxicology, University of Leipzig, Haertelstrasse 16-18, Leipzig, Germany.
J Biol Chem. 2007 Nov 23;282(47):33949-57. doi: 10.1074/jbc.M705840200. Epub 2007 Sep 21.
Whole cell patch clamp investigations were carried out to clarify the pH sensitivity of native and recombinant P2X(3) receptors. In HEK293 cells permanently transfected with human (h) P2X(3) receptors (HEK293-hP2X(3) cells), an acidic pH shifted the concentration-response curve for alpha,beta-methylene ATP (alpha,beta-meATP) to the right and increased its maximum. An alkalic pH did not alter the effect of alpha,beta-meATP. Further, a low pH value increased the activation time constant (tau(on)) of the alpha,beta-meATP current; the fast and slow time constants of desensitization (tau(des1), tau(des2)) were at the same time also increased. Finally, acidification accelerated the recovery of P2X(3) receptors from the desensitized state. Replacement of histidine 206, but not histidine 45, by alanine abolished the pH-induced effects on hP2X(3) receptors transiently expressed in HEK293 cells. Changes in the intracellular pH had no effect on the amplitude or time course of the alpha,beta-meATP currents. The voltage sensitivity and reversal potential of the currents activated by alpha,beta-meATP were unaffected by extracellular acidification. Similar effects were observed in a subpopulation of rat dorsal root ganglion neurons expressing homomeric P2X(3) receptor channels. It is suggested that acidification may have a dual effect on P2X(3) channels, by decreasing the current amplitude at low agonist concentrations (because of a decrease in the rate of activation) and increasing it at high concentrations (because of a decrease in the rate of desensitization). Thereby, a differential regulation of pain sensation during e.g. inflammation may occur at the C fiber terminals of small DRG neurons in peripheral tissues.
进行全细胞膜片钳研究以阐明天然和重组P2X(3)受体的pH敏感性。在稳定转染人（h）P2X(3)受体的HEK293细胞（HEK293-hP2X(3)细胞）中，酸性pH使α,β-亚甲基ATP（α,β-meATP）的浓度-反应曲线右移并增加其最大值。碱性pH不改变α,β-meATP的作用。此外，低pH值增加了α,β-meATP电流的激活时间常数（τ(on)）；脱敏的快速和慢速时间常数（τ(des1)，τ(des2)）同时也增加。最后，酸化加速了P2X(3)受体从脱敏状态的恢复。用丙氨酸取代组氨酸206而非组氨酸45消除了pH对HEK293细胞中瞬时表达的hP2X(3)受体的影响。细胞内pH的变化对α,β-meATP电流的幅度或时间进程没有影响。α,β-meATP激活的电流的电压敏感性和反转电位不受细胞外酸化的影响。在表达同聚体P2X(3)受体通道的大鼠背根神经节神经元亚群中观察到类似的效应。提示酸化可能对P2X(3)通道有双重作用，在低激动剂浓度下降低电流幅度（由于激活速率降低），在高浓度下增加电流幅度（由于脱敏速率降低）。因此，例如在炎症期间，在外周组织中小DRG神经元的C纤维终末可能发生对痛觉的差异性调节。
