Minke B, Payne R
Department of Neuroscience, Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
J Neurosci. 1991 Apr;11(4):900-9. doi: 10.1523/JNEUROSCI.11-04-00900.1991.
The spatial spread within fly photoreceptors of 2 forms of desensitization by bright light have been investigated: the natural process of light adaptation in normal Musca photoreceptors and a receptor-potential inactivation in the no-steady-state (nss) mutant of the sheep blowfly Lucilia. The suction-electrode method used for recording from vertebrate rods was applied to fly ommatidia. A single ommatidium in vitro was partially sucked into a recording pipette. Illumination of the portion of the ommatidium within the pipette resulted in a flow of current having a wave form similar to that of the receptor potential and polarity consistent with current flow into the illuminated region of the photoreceptors. Two 5-microns slits of light, positioned at right angles to the ommatidial axis, were employed to determine the spread of light adaptation or inactivation along the ommatidium. The intensity of a flash of light delivered to one (adapting) slit was adjusted until it produced a criterion fractional reduction in the response to the other (test) slit. The reciprocal of this intensity of the adapting slit was taken as a measure of the effectiveness of the slit in causing light adaptation or inactivation. The effectiveness of the slit in causing light adaptation in normal Musca ommatidia fell as the adapting and test slits were moved farther apart along the ommatidial axis, declining to half its maximal value at a distance of 13 +/- 2 microns. Similar measurements of the effectiveness of a slit in causing light-induced inactivation in the nss mutant of Lucilia also demonstrated localization, declining to half its maximal value at a distance between the slits of 9 +/- 1 microns. Neither light adaptation nor inactivation by the nss mutation, therefore, appear to be mediated by voltage or by a highly diffusible agent. The results are consistent with the idea that inactivation by the nss mutation replaces adaptation in the mutant photoreceptors.
正常家蝇光感受器中的自然光适应过程以及羊绿蝇 Lucilia 的非稳态（nss）突变体中的感受器电位失活。用于记录脊椎动物视杆细胞的吸力电极法被应用于果蝇小眼。将单个离体小眼部分吸入记录微管。对微管内小眼部分的光照导致电流流动，其波形类似于感受器电位，极性与流入光感受器光照区域的电流一致。使用与小眼轴成直角定位的两个 5 微米宽的光缝来确定光适应或失活沿小眼的传播。调整传递到一个（适应）光缝的闪光强度，直到它使对另一个（测试）光缝的反应产生标准分数降低。将该适应光缝的强度的倒数作为该光缝引起光适应或失活有效性的量度。随着适应光缝和测试光缝沿小眼轴距离增加，正常家蝇小眼光缝引起光适应的有效性下降，在 13±2 微米的距离处降至其最大值的一半。对 Lucilia 的 nss 突变体中光缝引起光诱导失活有效性的类似测量也显示出定位，在光缝间距离为 9±1 微米时降至其最大值的一半。因此，无论是光适应还是 nss 突变引起的失活，似乎都不是由电压或高度可扩散的介质介导的。结果与 nss 突变引起的失活替代突变体光感受器中的适应这一观点一致。
