Rectification of cGMP‐activated channels induced by phosphorylation in dogfish retinal ‘on’ bipolar cells
Rectification of cGMP‐activated channels induced by phosphorylation in dogfish retinal ‘on’ bipolar cells
复制标题
角鲨视网膜双极细胞磷酸化诱导的 cGMP 激活通道的校正
DOI：
10.1111/j.1469-7793.2001.00697.x
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
G. Falk
中科院分区：
文献类型：
--
作者：
R. Shiells;G. Falk
1从暗适应角鲨视网膜切片中的电压钳位“开启”双极细胞获得对短暂闪光的全细胞电流响应。当内部Ca 2+被缓冲到低水平时，它们的闪光响应的电流-电压（I-V）关系是线性的，反转电位接近0 mV。2在升高内部Ca 2+时，光依赖性I-V关系显示出向外整流，因此对于22 mV的超极化，对闪光的电流响应降低了e倍。3在贴片移液器溶液中加入CaMKII抑制肽，即使存在50 μm Ca 2+，也可消除整流。4这些结果与cGMP激活通道的CaMKII磷酸化一致，导致电导的电压依赖性降低（外向整流）和光响应降低。电压依赖性表明磷酸化在通道的外部附近产生能量屏障，主要减少一价阳离子的流动。这是第一个报道的CaMKII磷酸化作用将膜通道的电特性从线性改变为整流的实例。6背景光和通道整流引起的Ca 2+依赖性脱敏可能是光适应下视觉系统中心-周围组织变化的基础。
1 Whole‐cell current responses to brief flashes were obtained from voltage‐clamped ‘on’ bipolar cells in dark‐adapted dogfish retinal slices. When internal Ca2+ was buffered to low levels, the current‐voltage (I‐V) relation of their flash responses was linear, with a reversal potential near 0 mV. 2 On elevating internal Ca2+ the light‐dependent I‐V relation showed outward rectification, such that the current response to a flash decreased e‐fold for a hyperpolarization of 22 mV. 3 Inclusion of a CaMKII inhibitory peptide in the patch‐pipette solution removed the rectification even in the presence of 50 μm Ca2+. 4 These results are consistent with CaMKII phosphorylation of cGMP‐activated channels leading to a voltage‐dependent reduction in conductance (outward rectification) and a reduced light response. The voltage‐dependent property suggests that phosphorylation creates an energy barrier near the outer part of the channel, reducing the flow principally of monovalent cations. 5 This is the first reported instance of CaMKII phosphorylation acting to change the electrical characteristics of a membrane channel from linear to rectifying. 6 Ca2+‐dependent desensitization by background light and channel rectification may underlie the change in centre‐surround organization of the visual system with light adaptation.