Gating properties of the P2X2a and P2X2b receptor channels: experiments and mathematical modeling.

Anmar Khadra, Zonghe Yan, Claudio Coddou, Melanija Tomić, Arthur Sherman, Stanko S Stojilkovic
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引用次数: 32

Abstract

Adenosine triphosphate (ATP)-gated P2X2 receptors exhibit two opposite activation-dependent changes, pore dilation and pore closing (desensitization), through a process that is incompletely understood. To address this issue and to clarify the roles of calcium and the C-terminal domain in gating, we combined biophysical and mathematical approaches using two splice forms of receptors: the full-size form (P2X2aR) and the shorter form missing 69 residues in the C-terminal domain (P2X2bR). Both receptors developed conductivity for N-methyl-D-glucamine within 2-6 s of ATP application. However, pore dilation was accompanied with a decrease rather than an increase in the total conductance, which temporally coincided with rapid and partial desensitization. During sustained agonist application, receptors continued to desensitize in calcium-independent and calcium-dependent modes. Calcium-independent desensitization was more pronounced in P2X2bR, and calcium-dependent desensitization was more pronounced in P2X2aR. In whole cell recording, we also observed use-dependent facilitation of desensitization of both receptors. Such behavior was accounted for by a 16-state Markov kinetic model describing ATP binding/unbinding and activation/desensitization. The model assumes that naive receptors open when two to three ATP molecules bind and undergo calcium-independent desensitization, causing a decrease in the total conductance, or pore dilation, causing a shift in the reversal potential. In calcium-containing media, receptor desensitization is facilitated and the use-dependent desensitization can be modeled by a calcium-dependent toggle switch. The experiments and the model together provide a rationale for the lack of sustained current growth in dilating P2X2Rs and show that receptors in the dilated state can also desensitize in the presence of calcium.

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P2X2a和P2X2b受体通道的门控特性:实验和数学建模。
三磷酸腺苷(ATP)门控的P2X2受体表现出两种相反的激活依赖性变化,即孔扩张和孔关闭(脱敏),其过程尚不完全清楚。为了解决这个问题并阐明钙和c端结构域在门控中的作用,我们结合了生物物理和数学方法,使用了两种剪接形式的受体:全尺寸形式(P2X2aR)和c端结构域缺失69个残基的短形式(P2X2bR)。两种受体在ATP作用后2-6秒内对n -甲基- d -氨基葡萄糖产生导电性。然而,孔隙扩张伴随着总电导的减少而不是增加,这在时间上与快速和部分脱敏一致。在持续使用激动剂期间,受体继续以钙独立和钙依赖模式脱敏。钙非依赖性脱敏在P2X2bR中更为明显,钙依赖性脱敏在P2X2aR中更为明显。在全细胞记录中,我们还观察到两种受体的脱敏使用依赖性促进。这种行为被描述ATP结合/解结合和激活/脱敏的16态马尔可夫动力学模型所解释。该模型假设,当两到三个ATP分子结合并进行钙无关脱敏时,幼稚受体打开,导致总电导降低或孔扩张,导致逆转电位的移动。在含钙介质中,受体脱敏更容易,使用依赖性脱敏可以通过钙依赖性拨动开关来模拟。实验和模型共同提供了扩张P2X2Rs缺乏持续电流增长的基本原理,并表明处于扩张状态的受体在钙存在下也可以脱敏。
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