Hall M O, Abrams T
Jules Stein Eye Institute, University of California, Los Angeles, School of Medicine 90024-1771.
Exp Eye Res. 1987 Dec;45(6):907-22. doi: 10.1016/s0014-4835(87)80105-7.
Retinal pigment epithelial (RPE) cells selectively phagocytize rod outer segments (ROS) by a process which may be mediated by specific cell surface receptors. We have studied the kinetics of this process using rat RPE cells grown in tissue culture. By cooling RPE cells to 17 degrees C, the binding and ingestion phases of phagocytosis can be separated. Maximum ROS binding with minimum ingestion occurs at 17 degrees C; above 17 degrees C the rate of ingestion increases markedly. Thus it is possible to measure the kinetics of ROS binding to RPE cells at 17 degrees C and of ROS ingestion at 37 degrees C. At 17 degrees C, ROS binding is saturable, both with respect to time and to ROS concentration. ROS ingestion saturates after 4 hr of incubation at 37 degrees C, after which the cells are refractory to further ROS ingestion for 1-2 hr. During this recovery period, rapid digestion of the internalized ROS takes place. Cycloheximide, when present at a concentration (2 x 10(-5) M) which inhibits protein synthesis by 92%, has no effect on ROS phagocytosis or on the recovery of ROS ingestion at 37 degrees C. This suggests that if receptors mediate the ingestion of ROS by RPE cells, they are not degraded after the ROS are internalized. Dystrophic rat (RCS-p+) RPE cells exhibit normal binding, but very limited ingestion of ROS at 37 degrees C. The rate and amount of ROS binding to these cells at 37 degrees C is comparable with that occurring to normal cells at 17 degrees C. These observations support the hypothesis that there are a limited number of receptors which are specific for ROS binding on the surface of normal and dystrophic rat RPE cells.
视网膜色素上皮（RPE）细胞通过一个可能由特定细胞表面受体介导的过程选择性地吞噬视杆细胞外段（ROS）。我们利用组织培养中生长的大鼠RPE细胞研究了这一过程的动力学。通过将RPE细胞冷却至17℃，吞噬作用的结合和摄取阶段可以分开。在17℃时发生最大程度的ROS结合且摄取最少；高于17℃时，摄取速率显著增加。因此，有可能在17℃下测量ROS与RPE细胞结合的动力学以及在37℃下测量ROS摄取的动力学。在17℃时，ROS结合在时间和ROS浓度方面都是可饱和的。在37℃孵育4小时后，ROS摄取达到饱和，此后细胞在1 - 2小时内对进一步的ROS摄取不再敏感。在这个恢复期内，内化的ROS会迅速被消化。当环己酰亚胺以抑制蛋白质合成92%的浓度（2×10⁻⁵ M）存在时，对ROS吞噬作用或37℃下ROS摄取的恢复没有影响。这表明，如果受体介导RPE细胞摄取ROS，那么在ROS内化后它们不会被降解。营养不良大鼠（RCS - p⁺）的RPE细胞表现出正常的结合，但在37℃下对ROS的摄取非常有限。在37℃时，ROS与这些细胞结合的速率和量与正常细胞在17℃时相当。这些观察结果支持这样的假设，即在正常和营养不良大鼠RPE细胞表面存在数量有限的对ROS结合具有特异性的受体。
