Barash S, Suss E, Stavenga D G, Rubinstein C T, Selinger Z, Minke B
Department of Physiology, Hadassah Medical School, Hebrew University, Jerusalem, Israel.
J Gen Physiol. 1988 Sep;92(3):307-30. doi: 10.1085/jgp.92.3.307.
The nss (no steady state) phototransduction mutant of the sheep blowfly Lucilia was studied electrophysiologically using intracellular recordings. The effects of the nss mutation on the receptor potential are manifested in the following features of the light response. (a) The responses to a flash or to dim lights are close to normal, but the receptor potential decays close to the baseline level during prolonged illumination after a critical level of light intensity is reached. (b) The decline of the response is accompanied by a large reduction in responsiveness to light that recovers within 20 s in the dark. (c) The full reduction in responsiveness to light is reached when approximately 13% of the photopigment molecules are converted from rhodopsin (R) to metarhodopsin (M). (d) A maximal net pigment conversion from R to M by blue light induces persistent inactivation in the dark, without an apparent voltage response. This inactivation could be abolished at any time by M-to-R conversion with orange light. The above features of the mutant indicate that the effect of the nss mutation on the light response of Lucilia is very similar to the effects of the transient receptor potential (trp) mutation on the photoreceptor potential of Drosophila. Noise analysis and voltage measurements indicate that the decay of the receptor potential is due to a severe reduction in the rate of occurrence of the elementary voltage responses (bumps). The bumps are only slightly modified in shape and amplitude during the decline of the response to light of medium intensity. There is also a large increase in response latency during intense background illumination. These results are consistent with the hypothesis that separate, independent mechanisms determine bump triggering and bump shape and amplitude. The nss mutation affects the triggering mechanism of the bump.
利用细胞内记录技术，对绵羊绿蝇丽蝇的nss（非稳态）光转导突变体进行了电生理学研究。nss突变对感受器电位的影响体现在光反应的以下特征中。(a) 对闪光或暗光的反应接近正常，但在达到临界光强度后长时间光照期间，感受器电位会衰减至接近基线水平。(b) 反应的下降伴随着对光的反应性大幅降低，在黑暗中20秒内恢复。(c) 当约13%的光色素分子从视紫红质（R）转化为变视紫红质（M）时，对光的反应性完全降低。(d) 蓝光使R到M的最大净色素转化率在黑暗中诱导持续失活，无明显电压反应。这种失活可在任何时候通过橙光将M转化为R来消除。突变体的上述特征表明，nss突变对丽蝇光反应的影响与瞬时受体电位（trp）突变对果蝇光感受器电位的影响非常相似。噪声分析和电压测量表明，感受器电位的衰减是由于基本电压反应（脉冲）发生率的严重降低。在对中等强度光的反应下降期间，脉冲的形状和幅度仅略有改变。在强烈背景光照下，反应潜伏期也大幅增加。这些结果与以下假设一致，即单独、独立的机制决定脉冲触发以及脉冲形状和幅度。nss突变影响脉冲的触发机制。
