Light responses and light adaptation in rat retinal rods at different temperatures
Light responses and light adaptation in rat retinal rods at different temperatures
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DOI：
10.1113/jphysiol.2005.090662
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发表时间：
2005-09-15
影响因子：
5.5
通讯作者：
Koskelainen, A
中科院分区：
文献类型：
--
作者：
Nymark, S;Heikkinen, H;Koskelainen, A
在不同温度和稳定背景光强度下，将注射天冬氨酸的大鼠视网膜上的视网膜电图（ERG）质量电势记录为视杆细胞对短暂光脉冲的反应。目的是澄清哺乳动物和两栖动物视杆细胞之间的敏感性、反应动力学和光适应差异在多大程度上可以通过温度和外节大小来解释，而不假设光转导分子的功能差异。文献中有关两栖动物杆的相应信息由蟾蜍视网膜的新记录补充。所有光强度均表示为每棒光致异构化 (Rh*)。在大鼠视网膜中，估计有 34% 峰值敏感波长的入射光子引起视杆细胞的异构化，因为（六边形排列的）外部节段尺寸为 1.7 μm x 22 μm，平均比吸光度为 0.016 μm(-1)。大鼠和蟾蜍杆在黑暗中的分数敏感性（S）以类似的方式随着冷却而增加，但大鼠功能作为一个整体被转移到约 0.7 个对数单位的更高敏感性水平。这种差异可以通过大鼠视杆外节较小的尺寸来充分解释，因为激活视紫红质对磷酸二酯酶（PDE）的激活率相同，会导致 cGMP 浓度下降更快，因此大鼠的反应比蟾蜍更大。在 15-25 摄氏度范围内，在任何给定温度下，大鼠和蟾蜍的暗适应暗闪光光响应的波形和绝对时间尺度相似，尽管达到峰值时间 (t(p)) 的总体温度依赖性在大鼠中稍陡一些（Q(10) 近似于 4，而与 2-3 相比）。在相同温度下测量时，大鼠和两栖动物视杆细胞的光适应相似。在 12 摄氏度下，S 降低 1 个对数单位的平均背景强度在 20-50 Rh* s(-1) 范围内，而在 36 摄氏度下，大鼠视杆细胞中的平均背景强度约为 4500 Rh* s(-1)。我们的结论是，没有必要假设光转导分子的功能特性存在重大差异，以解释哺乳动物和两栖动物视杆细胞响应特性的差异。
Rod responses to brief pulses of light were recorded as electroretinogram (ERG) mass potentials across isolated, aspartate-superfused rat retinas at different temperatures and intensities of steady background light. The objective was to clarify to what extent differences in sensitivity, response kinetics and light adaptation between mammalian and amphibian rods can be explained by temperature and outer-segment size without assuming functional differences in the phototransduction molecules. Corresponding information for amphibian rods from the literature was supplemented by new recordings from toad retina. All light intensities were expressed as photoisomerizations per rod (Rh*). In the rat retina, an estimated 34% of incident photons at the wavelength of peak sensitivity caused isomerizations in rods, as the (hexagonally packed) outer segments measured 1.7 mu m x 22 mu m and had specific absorbance of 0.016 mu m(-1) on average. Fractional sensitivity (S) in darkness increased with cooling in a similar manner in rat and toad rods, but the rat function as a whole was displaced to a ca 0.7 log unit higher sensitivity level. This difference can be fully explained by the smaller dimensions of rat rod outer segments, since the same rate of phosphodiesterase (PDE) activation by activated rhodopsin will produce a faster drop in cGMP concentration, hence a larger response in rat than in toad. In the range 15-25 degrees C, the waveform and absolute time scale of dark-adapted dim-flash photoresponses at any given temperature were similar in rat and toad, although the overall temperature dependence of the time to peak (t(p)) was somewhat steeper in rat (Q(10) approximate to 4 versus 2-3). Light adaptation was similar in rat and amphibian rods when measured at the same temperature. The mean background intensity that depressed S by 1 log unit at 12 degrees C was in the range 20-50 Rh* s(-1) in both, compared with ca 4500 Rh* s(-1) in rat rods at 36 degrees C. We conclude that it is not necessary to assume major differences in the functional properties of the phototransduction molecules to account for the differences in response properties of mammalian and amphibian rods.