Hsiao Bernard, Mihalak Karla B, Magleby Karl L, Luetje Charles W
Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, FL 33101, USA.
J Neurophysiol. 2008 Feb;99(2):999-1007. doi: 10.1152/jn.01040.2007. Epub 2007 Dec 19.
Micromolar zinc potentiates neuronal nicotinic acetylcholine receptors (nAChRs) in a subtype-dependent manner. Zinc potentiates receptor function even at saturating agonist concentrations, without altering the receptor desensitization rate. Potentiation could occur through an increase in the number of available receptors, an increase in single-channel current amplitude, or an increase in single-channel open probability. To distinguish among these possibilities, we examined rat neuronal nAChRs expressed in Xenopus oocytes. Blockade of a large fraction of ACh activated alpha4beta4 or alpha4beta2 receptors by the open channel blocker hexamethonium failed to change the extent of potentiation by zinc, suggesting that zinc does not change the number of available receptors. The single-channel amplitudes of ACh (1 microM) activated alpha4beta4 receptors in outside-out patches were similar in the absence and the presence of 100 microM zinc (3.0 +/- 0.1 and 2.9 +/- 0.1 pA, respectively). To determine the effect of zinc on single-channel open probability, we examined alpha4beta4 receptors in cell-attached patches. The open probability at 100 nM ACh (0.011 +/- 0.002) was increased 4.5-fold by 100 microM zinc (0.050 +/- 0.008), accounting for most of the potentiation observed at the whole cell level. The increase in open probability was due to an increase in burst duration, which increased from 207 +/- 38 ms in the absence of zinc to 830 +/- 189 ms in the presence of zinc. Our results suggest that potentiation of neuronal nAChRs by zinc is due to a stabilization of the bursting states of the receptor.
微摩尔浓度的锌以亚型依赖的方式增强神经元烟碱型乙酰胆碱受体（nAChRs）。即使在激动剂浓度饱和时，锌也能增强受体功能，而不改变受体的脱敏速率。增强作用可能通过增加可用受体的数量、增加单通道电流幅度或增加单通道开放概率来实现。为了区分这些可能性，我们研究了非洲爪蟾卵母细胞中表达的大鼠神经元nAChRs。开放通道阻滞剂六甲铵对大部分乙酰胆碱激活的α4β4或α4β2受体的阻断未能改变锌增强的程度，这表明锌不会改变可用受体的数量。在有无100μM锌的情况下，外向膜片上乙酰胆碱（1μM）激活的α4β4受体的单通道幅度相似（分别为3.0±0.1和2.9±0.1 pA）。为了确定锌对单通道开放概率的影响，我们研究了细胞贴附膜片中的α4β4受体。100 nM乙酰胆碱时的开放概率（0.011±0.002）在100μM锌存在时增加了4.5倍（0.050±0.008），这解释了在全细胞水平观察到的大部分增强作用。开放概率的增加是由于爆发持续时间的增加，从无锌时的207±38 ms增加到有锌时的830±189 ms。我们的结果表明，锌对神经元nAChRs的增强作用是由于受体爆发状态的稳定。
