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[Mg(2+) inhibits ATP-activated current mediated by rat P2X4 receptors expressed in Xenopus oocytes.] [Article in Chinese]

PENG Fang, ZHANG Yu-Qin^*, ZENG Yan, ZHOU Yan-Ling

Department of Physiology, Medical College, Wuhan University of Science and Technology, Wuhan 430065, China

Abstract

To investigate the modulation of Mg2+ on rat P2X4 receptors and its underlying mechanism, we transcribed cDNA coding for wild-type and mutant P2X4 receptors to cRNA in vitro, injected the cRNA to oocytes of Xenopus laevis using the microinjection technique and revealed the effect of Mg2+ on ATP-activated currents (IATP) mediated by P2X4 receptors using the two-electrode whole-cell voltage clamp technique. The effects of extracellular Mg2+ on IATP were as follows: (1) In oocytes expressing P2X4 receptors, Mg2+ with concentration ranging from 0.5–10 mmol/L inhibited the amplitude of IATP in a concentration-dependent and reversible manner, with a 50% inhibitory concentration value (IC50) of (1.24 ± 0.07) mmol/L for current activated by 100 μmol/L ATP. (2) Mg2+ (1 mmol/L) shifted the dose-response curve for IATP right-downward without changing the EC50, but reduced the maximal current (Emax) by (42.0 ± 2.1)%. (3) After being preincubated with Mg2+ for 80 s, the inhibitory effect of the Mg2+ on IATP reached the maximum. (4) The inhibition of Mg2+ on IATP was independent of membrane potential from −120 mV to +60 mV. (5) Compared with the current activated by 100 μmol/L ATP in the wild-type P2X4 receptors, mutant P2X4 D280Q responded to the application of 100 μmol/L ATP with a smaller current. The peak current was only (4.12 ± 0.15)% of that seen in wild-type receptors. Mutant P2X4 D280E responded to ATP stimulation with a current similar to that observed in cells expressing wild-type receptors. (6) When Asp280 was removed from P2X4, the current amplitude of IATP was increased almost one-fold, and Mg2+ with concentration ranging from 0.5–10 mmol/L did not affect the IATP significantly. The results suggest that Mg2+ inhibits IATP mediated by P2X4 receptors non-competitively, reversibly, concentration-dependently, time-dependently and voltage-independently. The inhibitory effect of Mg2+ might be realized by acting on the site Asp280 of the P2X4 receptors.

Key words: Mg2+; ATP-activated current; Xenopus oocytes; two-electrode voltage clamp technique

Received: 2011-07-06　　Accepted: 2011-11-03

Corresponding author: 张玉芹　　E-mail: zhangyuqin@wust.edu.cn

Citing This Article：

PENG Fang, ZHANG Yu-Qin, ZENG Yan, ZHOU Yan-Ling. [Mg(2+) inhibits ATP-activated current mediated by rat P2X4 receptors expressed in Xenopus oocytes.] [Article in Chinese]. Acta Physiol Sin 2012; 64 (1): 75-81 (in Chinese with English abstract).