TURNOVER OF ROD PHOTORECEPTOR OUTER SEGMENTS .1. MEMBRANE ADDITION AND LOSS IN RELATIONSHIP TO TEMPERATURE
TURNOVER OF ROD PHOTORECEPTOR OUTER SEGMENTS .1. MEMBRANE ADDITION AND LOSS IN RELATIONSHIP TO TEMPERATURE
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DOI：
10.1083/jcb.75.2.490
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发表时间：
1977-01-01
影响因子：
7.8
通讯作者：
RAYBORN, ME
中科院分区：
文献类型：
--
作者：
HOLLYFIELD, JG;BESHARSE, JC;RAYBORN, ME
Membrane turnover in outer segments of Rana pipiens red rods (ROS [rod outer segment]) was studied in tadpoles maintained under cyclic lighting (12L[light]:12D[dark]) at 23.degree., 28.degree. and 33.degree. C. Large fragments (> 2 .mu.m in diameter or length) were shed from the ROS tips shortly after the onset of light. These were phagocytized by the pigment epithelium (PE) which caused an increase in the number of phagosomes > 2 .mu.m in size (large phagosomes). Large phagosomes were present in highest numbers 2-4 h after light exposure and were degraded by 8-12 h. The proportion of ROS that shed each day after the onset of the light cycle increased with increment increases in temperatures (23.degree. C-18%, 28.degree. C-33%, 33.degree. C-42% per day), resulting in a reduction in the average interval of time between repeated sheddings (23.degree. C-5.6 days, 28.degree. C-3 days, 33.degree. C-2.4 days) though the average numbers of disks shed from ROS at the various temperatures were not significantly different (23.degree. C-139.5 .+-. 5.7, 28.degree. C-129.4 .+-. 7.6, 33.degree. C-129.9 .+-. 4.8 disks/shed packet). Phagosomes in the PE that were < 2 .mu.m in diameter (small phagosomes) were present in relatively constant numbers throughout the day, and their numbers increased at higher temperatures. The absence of a concomitant increase in small phagosomes as large phagosomes were degraded indicates that large phagosomes were not the major source of small phagosomes. When the PE was isolated to culture in the absence of the retina, these small phagosomes were degraded. The rate of disk addition to the ROS base was determined by autoradiography after [3H]leucine injection. The number of disks added per day increased with elevations of temperature (23.degree. C-32.4; 28.degree. C-55.9; 33.degree. C-65.5). The average number of disks added to the ROS between repeated sheddings (23.degree. C-181.4; 28.degree. C-167.7; 33.degree. C-157.2) was greater than the number of disks shed after light exposure. Inasmuch as the ROS showed no net increase in length during the tadpole stages utilized, the remaining disks must be lost at some other time. EM analysis revealed the presence of small groups of disks in curled configurations at the tips of ROS, suggesting possible stages of detachment. These irregular disk configurations were identical in size to the small phagosomes in the PE, and they were observed at all fixation times studied throughout the day. The loss of groups of small disks from the ROS tips accounted for approximately 20% of the total disk turnover. The remaining 80% were shed after the onset of the light cycle.
