Wong F, Knight B W, Dodge F A
J Gen Physiol. 1982 Jun;79(6):1089-113. doi: 10.1085/jgp.79.6.1089.
Light-evoked current fluctuations have been recorded from ventral photoreceptors of Limulus for light intensity from threshold up to 10(5) times threshold. These data are analyzed in terms of the adapting bump noise model, which postulates that (a) the response to light is a summation of bumps; and (b) the average size of bump decreases with light intensity, and this is the major mechanism of light adaptation. It is shown here that this model can account for the data well. Furthermore, the model provides a convenient framework to characterize, in terms of bump parameters, the effects of calcium ions, which are known to affect photoreceptor functions. From responses to very dim light, it is found that the average impulse response (average of a large number of responses to dim flashes) can be predicted from knowledge of both the noise characteristics under steady light and the dispersion of latencies of individual bumps. Over the range of light intensities studied, it is shown that (a) the bump rate increases in strict proportionality to light intensity, up to approximately 10(5) bumps per second; and (b) the bump height decreases approximately as the -0.7 power of light intensity; at rates greater than 10(5) bumps per second, the conductance change associated with the single bump seems to reach a minimum value of approximately 10(-11) reciprocal ohms; (c) from the lowest to the highest light intensity, the bump duration decreases approximately by a factor of 2, and the time scale of the dispersion of latencies of individual bumps decreases approximately by a factor of 3; (d) removal of calcium ions from the bath lengthens the latency process and causes an increase in bump height but appears to have no effect on either the bump rate or the bump duration.
已记录了美洲鲎腹侧光感受器在光强度从阈值到阈值的10⁵倍范围内的光诱发电流波动。这些数据根据适应性脉冲噪声模型进行分析，该模型假定：(a) 对光的响应是脉冲的总和；(b) 脉冲的平均大小随光强度降低，这是光适应的主要机制。结果表明，该模型能够很好地解释这些数据。此外，该模型提供了一个方便的框架，可根据脉冲参数来描述已知会影响光感受器功能的钙离子的作用。从对极暗光的响应中发现，平均脉冲响应（对暗光闪烁的大量响应的平均值）可根据稳定光照下的噪声特性和单个脉冲潜伏期的离散情况来预测。在所研究的光强度范围内，结果表明：(a) 脉冲频率与光强度严格成正比增加，最高可达每秒约10⁵个脉冲；(b) 脉冲高度大约随光强度的-0.7次方降低；在频率大于每秒10⁵个脉冲时，与单个脉冲相关的电导变化似乎达到约10⁻¹¹倒数欧姆的最小值；(c) 从最低到最高光强度，脉冲持续时间大约减少2倍，单个脉冲潜伏期离散的时间尺度大约减少3倍；(d) 从浴中去除钙离子会延长潜伏期过程并导致脉冲高度增加，但似乎对脉冲频率或脉冲持续时间均无影响。
