Luo Dong-Gen, Yau King-Wai
Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
J Gen Physiol. 2005 Sep;126(3):263-9. doi: 10.1085/jgp.200509342.
We have measured the sensitivity of rod photoreceptors isolated from overnight dark-adapted mice of age P12 (neonate) through P45 (adult) with suction-pipette recording. During this age period, the dark current increased roughly in direct proportion to the length of the rod outer segment. In the same period, the flash sensitivity of rods (reciprocal of the half-saturating flash intensity) increased by approximately 1.5-fold. This slight developmental change in sensitivity was not accentuated by dark adapting the animal for just 1 h or by increasing the ambient luminance by sixfold during the prior light exposure. The same small, age-dependent change in rod sensitivity was found with rat. After preincubation of the isolated retina with 9-cis-retinal, neonatal mouse rods showed the same sensitivity as adult rods, suggesting the presence of a small amount of free opsin being responsible for their lower sensitivity. The sensitivity of neonate rods could also be increased to the adult level by dark adapting the animal continuously for several days. By comparing the sensitivity of neonate rods in darkness to that of adult rods after light bleaches, we estimated that approximately 1% of rod opsin in neonatal mouse was devoid of chromophore even after overnight dark adaptation. Overall, we were unable to confirm a previous report that a 50-fold difference in rod sensitivity existed between neonatal and adult rats.
我们使用吸管记录法测量了从出生后12天（新生小鼠）到45天（成年小鼠）经一夜暗适应的小鼠分离出的视杆光感受器的敏感性。在这个年龄段，暗电流大致与视杆外段的长度成正比增加。在同一时期，视杆的闪光敏感性（半饱和闪光强度的倒数）增加了约1.5倍。这种敏感性的轻微发育变化不会因仅让动物暗适应1小时或在先前的光照期间将环境亮度提高6倍而加剧。在大鼠中也发现了视杆敏感性随年龄的相同微小变化。用9-顺式视黄醛预孵育分离的视网膜后，新生小鼠视杆显示出与成年视杆相同的敏感性，这表明存在少量游离视蛋白导致其敏感性较低。通过连续几天对动物进行暗适应，新生视杆的敏感性也可以提高到成年水平。通过比较新生视杆在黑暗中的敏感性与光漂白后成年视杆的敏感性，我们估计即使经过一夜暗适应，新生小鼠中仍约有1%的视杆视蛋白没有发色团。总体而言，我们无法证实之前的一份报告，即新生大鼠和成年大鼠的视杆敏感性存在50倍的差异。
