van Hateren J H, Lamb T D
Department of Neurobiophysics, University of Groningen, Groningen, The Netherlands.
BMC Neurosci. 2006 Apr 20;7:34. doi: 10.1186/1471-2202-7-34.
The precise form of the light response of human cone photoreceptors in vivo has not been established with certainty. To investigate the response shape we compare the predictions of a recent model of transduction in primate cone photoreceptors with measurements extracted from human cones using the paired-flash electroretinogram method. As a check, we also compare the predictions with previous single-cell measurements of ground squirrel cone responses.
The predictions of the model provide a good description of the measurements, using values of parameters within the range previously determined for primate retina. The dim-flash response peaks in about 20 ms, and flash responses at all intensities are essentially monophasic. Three time constants in the model are extremely short: the two time constants for inactivation (of visual pigment and of transducin/phosphodiesterase) are around 3 and 10 ms, and the time constant for calcium equilibration lies in the same range.
The close correspondence between experiment and theory, using parameters previously derived for recordings from macaque retina, supports the notion that the electroretinogram approach and the modelling approach both provide an accurate estimate of the cone photoresponse in the living human eye. For reasons that remain unclear, the responses of isolated photoreceptors from the macaque retina, recorded previously using the suction pipette method, are considerably slower than found here, and display biphasic kinetics.
人类视锥光感受器在体内的光反应精确形式尚未确定。为了研究反应形式，我们将灵长类视锥光感受器转导的最新模型预测结果与使用双闪光视网膜电图方法从人类视锥中提取的测量值进行了比较。作为检验，我们还将这些预测结果与之前对松鼠视锥反应的单细胞测量结果进行了比较。
该模型的预测结果能够很好地描述测量值，所使用的参数值在先前为灵长类视网膜确定的范围内。暗闪光反应在约20毫秒时达到峰值，所有强度的闪光反应基本上都是单相的。模型中的三个时间常数极短：视觉色素和转导素/磷酸二酯酶失活的两个时间常数约为3毫秒和10毫秒，钙平衡的时间常数也在同一范围内。
使用先前从猕猴视网膜记录中得出的参数，实验与理论之间的密切对应支持了这样一种观点，即视网膜电图方法和建模方法都能准确估计活体人眼中视锥的光反应。出于尚不清楚的原因，先前使用吸管法记录的猕猴视网膜分离光感受器的反应比这里发现的要慢得多，并且呈现双相动力学。
