Li J D, Govardovskii V I, Steinberg R H
Department of Physiology, University of California, San Francisco 94143-0444.
Vis Neurosci. 1994 Jul-Aug;11(4):743-52. doi: 10.1017/s0952523800003047.
We have studied the effect of retinal illumination on the concentration of the extracellular space marker tetramethylammonium (TMA+) in the dark-adapted cat retina using double-barreled ion-selective microelectrodes. The retina was loaded with TMA+ by a single intravitreal injection. Retinal illumination produced a slow decrease in [TMA+]o, which was maximal in amplitude in the most distal portion of the space surrounding photoreceptors, the subretinal space. The light-evoked decrease in [TMA+]o was considerably slower and of a different overall time course than the light-evoked decrease in [K+]o, also recorded in the subretinal space. [TMA+]o decreased to a peak at 38 s after the onset of illumination, then slowly recovered towards the baseline, and transiently increased following the offset of illumination. It resembled the light-evoked [TMA+]o decreases previously recorded in the in vitro preparations of frog (Huang & Karwoski, 1990, 1992) and chick (Li et al., 1992, 1994) but was considerably larger in amplitude, 22% compared with 7%. As in frog, where it was first recorded, the light-evoked [TMA+]o decrease is considered to originate from a light-evoked increase in the volume of the subretinal space (or subretinal hydration). A mathematical model accounting for [TMA+]o diffusion predicted that the volume increase underlying the response was 63% on average and could be as large as 95% and last for minutes. The estimated volume increase was then used to examine its effect on K+ concentration in the subretinal space. We conclude that a light-dependent hydration of the subretinal space represents a significant physiological event in the intact cat eye, which should affect the organization of the interphotoreceptor matrix, and the concentrations of all ions and metabolites located in the subretinal space.
我们使用双管离子选择性微电极，研究了视网膜光照对暗适应猫视网膜中细胞外空间标记物四甲基铵（TMA+）浓度的影响。通过单次玻璃体内注射将TMA+注入视网膜。视网膜光照使[TMA+]o缓慢下降，在光感受器周围空间最远端的视网膜下空间，其幅度最大。视网膜光照引起的[TMA+]o下降比同样在视网膜下空间记录到的光照引起的[K+]o下降要慢得多，且整体时间进程不同。光照开始后38秒，[TMA+]o下降至峰值，然后缓慢恢复至基线，并在光照停止后短暂升高。它类似于先前在青蛙（Huang & Karwoski，1990年，1992年）和小鸡（Li等人，1992年，1994年）的体外制剂中记录到的光照引起的[TMA+]o下降，但幅度要大得多，分别为22%和7%。与首次记录到这种现象的青蛙一样，光照引起的[TMA+]o下降被认为源于视网膜下空间体积（或视网膜下水合作用）的光照诱导增加。一个解释[TMA+]o扩散的数学模型预测，响应背后的体积增加平均为63%，可能高达95%，并持续数分钟。然后，利用估计的体积增加来研究其对视网膜下空间K+浓度的影响。我们得出结论，视网膜下空间的光依赖性水合作用是完整猫眼的一个重要生理事件，它应该会影响光感受器间基质的组织以及位于视网膜下空间的所有离子和代谢物的浓度。
