Haugh-Scheidt L M, Griff E R, Linsenmeier R A
Department of Biomedical Engineering, Northwestern University, Evanston, IL 60208, USA.
Exp Eye Res. 1995 Jul;61(1):73-81. doi: 10.1016/s0014-4835(95)80060-3.
Transient changes in retinal oxygen in response to light stimuli were studied to further understand the light-evoked change in oxygen consumption. Double-barreled microelectrodes, which measured oxygen and local voltage simultaneously, were positioned near the photoreceptor inner segments of the toad neural retina-retinal pigment epithelium-choroid preparation. Light-evoked oxygen responses were measured in a normal [Na+] solution, and in a test solution with lowered extracellular [Na+] to inhibit Na+/K+ pumping. Under the normal [Na+] condition, retinal oxygen tension increased in response to light indicating that oxygen utilization had decreased. When the Na+ concentration was lowered in the retina, the oxygen tension decreased in response to light, indicating an increase in oxygen utilization which was smaller than the Na+/K+ pump effect and therefore masked under normal conditions. The increase in oxygen utilization in lowered [Na+] was suppressed by adding 0.7 mM 3-isobutyl-1-methyl-xanthine, a phosphodiesterase inhibitor, suggesting that the response was largely due to hydrolysis and subsequent resynthesis of cyclic GMP. Results of fitting the light-evoked responses to exponential functions suggested that the decrease in oxygen consumption caused by slowing of the photoreceptor Na+/K+ ATPase had a time constant between 130 and 180 sec and that the increase in oxygen utilization from increased cyclic GMP synthesis was faster.
为了进一步了解光诱发的氧消耗变化，研究了视网膜氧对光刺激的瞬态变化。双管微电极可同时测量氧和局部电压，将其放置在蟾蜍神经视网膜-视网膜色素上皮-脉络膜标本的光感受器内段附近。在正常[Na⁺]溶液和细胞外[Na⁺]降低以抑制Na⁺/K⁺泵浦的测试溶液中测量光诱发的氧反应。在正常[Na⁺]条件下，视网膜氧张力对光的反应增加，表明氧利用率降低。当视网膜中Na⁺浓度降低时，氧张力对光的反应降低，表明氧利用率增加，但其增加幅度小于Na⁺/K⁺泵的作用，因此在正常条件下被掩盖。通过添加0.7 mM的3-异丁基-1-甲基黄嘌呤（一种磷酸二酯酶抑制剂），可抑制低[Na⁺]时氧利用率的增加，这表明该反应主要是由于环磷酸鸟苷的水解和随后的再合成。将光诱发反应拟合为指数函数的结果表明，光感受器Na⁺/K⁺ ATP酶减慢导致的氧消耗减少的时间常数在130至180秒之间，并且环磷酸鸟苷合成增加导致的氧利用率增加更快。
