Chromophore switch from 11-cis-dehydroretinal (A2) to 11-cis-retinal (A1) decreases dark noise in salamander red rods
Chromophore switch from 11-cis-dehydroretinal (A2) to 11-cis-retinal (A1) decreases dark noise in salamander red rods
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DOI：
10.1113/jphysiol.2007.142935
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发表时间：
2007-11-15
影响因子：
5.5
通讯作者：
Cornwall, M. Carter
中科院分区：
文献类型：
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作者：
Ala-Laurila, Petri;Donner, Kristian;Cornwall, M. Carter
在虎蝾螈幼体视网膜离体杆状体的膜电流中记录了大部分天然视色素漂白前后的暗噪声、光致噪声和对短暂闪光的响应，这些视色素主要具有11-顺式-3,4-脱氢视网膜（A2）色团，并与11-顺式视网膜（A1）色团在同一离体杆状体中再生。目的是测试这样一个假设，即通过从A2切换到A1将色素蓝移会降低自发热激活的速率，从而降低棒中固有的光样噪声。在5个细胞（21℃）中获得完整的记录。根据最大吸光度波长λ (max),(A1) = 502 nm和λ (max),(A2) = 528 nm，由光杆光谱灵敏度和吸光度测定的平均A2: A1比值在原始状态近似为0.74:0.26，在最终状态近似为0.09:0.91。在原生（A2）状态下，单量子响应（SQR）的振幅为0.41 +/- 0.03 pA，积分时间为3.16 +/- 0.15 s（平均+/- s.e.m.）。暗噪声功率谱的低频分支与离散类sqr事件一致，发生频率为0.238 +/- 0.026杆（-1）s（-1）。最终状态对应的值分别为0.57 +/- 0.07 pA （SQR振幅）、3.47 +/- 0.26 s（SQR积分时间）和0.030 +/- 0.006棒（-1）s(-1)（暗事件率）。因此，在天然状态和终态之间，每杆暗事件的速率和A2色素的比例都改变了约8倍，这表明即使在终态，暗事件也主要起源于A2分子。通过外推事件率和A2分数之间的线性关系到0% A2 （100% A1）和100% A2 (0% A1)，我们估计A1色素至少比A2色素稳定36倍。在原始（A2）状态下，离散暗事件的噪声分量占总暗电流方差的73%，在最终状态下占46%。剩余的“连续”噪声分量的功率谱在两种状态之间没有差异。在原生（A2）状态下，更小更快的SQR与杆的行为似乎和光适应黑暗事件的想法是一致的，黑暗事件发生的频率几乎为一次。与原始（A2）状态相比，暗噪声水平的降低和SQR幅度的增加都显著提高了蝾螈杆在A1发色团存在下的弱光下光子检测的可靠性。
Dark noise, light-induced noise and responses to brief flashes of light were recorded in the membrane current of isolated rods from larval tiger salamander retina before and after bleaching most of the native visual pigment, which mainly has the 11-cis-3,4-dehydroretinal(A2) chromophore, and regenerating with the 11-cis-retinal(A1) chromophore in the same isolated rods. The purpose was to test the hypothesis that blue-shifting the pigment by switching from A2 to A1 will decrease the rate of spontaneous thermal activations and thus intrinsic light-like noise in the rod. Complete recordings were obtained in five cells (21 degrees C). Based on the wavelength of maximum absorbance,lambda(max),(A1) = 502 nm and lambda(max),(A2) = 528 nm, the average A2 : A1 ratio determined from rod spectral sensitivities and absorbances was similar to 0.74:0.26 in the native state and similar to 0.09 : 0.91 in the final state. In the native (A2) state, the single-quantum response (SQR) had an amplitude of 0.41 +/- 0.03 pA and an integration time of 3.16 +/- 0.15 s ( mean +/- S. E. M.). The low-frequency branch of the dark noise power spectrum was consistent with discrete SQR-like events occurring at a rate of 0.238 +/- 0.026 rod(-1) s(-1). The corresponding values in the final state were 0.57 +/- 0.07 pA (SQR amplitude), 3.47 +/- 0.26 s (SQR integration time), and 0.030 +/- 0.006 rod(-1) s(-1) (rate of dark events). Thus the rate of dark events per rod and the fraction of A2 pigment both changed by ca 8-fold between the native and final states, indicating that the dark events originated mainly in A2 molecules even in the final state. By extrapolating the linear relation between event rates and A2 fraction to 0% A2 (100% A1) and 100% A2 (0% A1), we estimated that the A1 pigment is at least 36 times more stable than the A2 pigment. The noise component attributed to discrete dark events accounted for 73% of the total dark current variance in the native (A2) state and 46% in the final state. The power spectrum of the remaining 'continuous' noise component did not differ between the two states. The smaller and faster SQR in the native (A2) state is consistent with the idea that the rod behaves as if light-adapted by dark events that occur at a rate of nearly one per integration time. Both the decreased level of dark noise and the increased SQR amplitude must significantly improve the reliability of photon detection in dim light in the presence of the A1 chromophore compared to the native ( A2) state in salamander rods.