title: Turnover of rod photoreceptor outer segments. II. Membrane addition and loss in relationship to light.
abstract: The rate of disk addition to rod outer segments (ROS) varies widely in Xenopus laevis tadpoles kept in cyclic light (12L:12D). When measured as radioactive band (3H-band) displacement during the 2nd day after injection of [3H]leucine, 75% of the daily increment of displacement occurred during the first 8 h of light. During the same interval, the number of open disks at the ROS base increased more than threefold. During the last 8 h of darkness, 3H-band displacement was undetectable and the number of open disks was reduced. These observations suggest the possibility that disk addition may occur discontinuously. During the 3rd and 4th days after injection of [3H]leucine, maximal displacement of the 3H-band occurred later in the day than on the 2nd day, its movement no longer corresponding to the increase in open disks. This delay in 3H-band displacement may reflect a time delay as a result of propagation of compressive stress in an elastic ROS system. Maximal disk loss from ROS as reflected in counts of phagosomes in the pigment epithelium occurred within 1 h of light exposure, and phagosome counts remained high for 4 h before declining to a low level in darkness. Modified lighting regimes affected the daily rhythms of shedding and disk addition differently, suggesting that control mechanisms for the two processes are not directly coupled. During 3 days in darkness, disk addition was reduced 50% compared to controls (12L:12D), whereas shedding was reduced by about 40%. Although reduced in level, shedding occurred as a free-running circadian rhythm. There was no evidence of rhythmicity of disk addition in darkness. In constant light, the rate of disk addition was not different from controls, but shedding was reduced by about 80% after the 1st day. This resulted in a 21% increase in ROS length. Among animals kept on a 2.5L:21.5D cycle, the rate of disk addition was reduced by 40% while shedding was maintained near control levels, resulting in a slight decrease in ROS length. These observations indicate that normal shedding requires alternating light and darkness, and that the daily rhythm of disk addition is due primarily to daily stimulation by light.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000528:radiation effects / Q000648:ultrastructure; D008027:Light; D008854:Microscopy, Electron; D010588:Phagosomes / Q000648:ultrastructure; D010786:Photoreceptor Cells / Q000502:physiology* / Q000648:ultrastructure; D012374:Rod Cell Outer Segment / Q000502:physiology* / Q000648:ultrastructure; D014981:Xenopus
references.citation: J Cell Biol. 1967 Apr;33(1):61-72
references.pmid: 6033942
references.citation: J Ultrastruct Res. 1963 Dec;41:484-96
references.pmid: 14091928
references.citation: C R Seances Soc Biol Fil. 1963;157:2136-40
references.pmid: 14137420
references.citation: J Ultrastruct Res. 1964 Dec;11:581-602
references.pmid: 14244179
references.citation: J Cell Biol. 1971 May 1;49(2):303-18
references.pmid: 19866760
references.citation: Exp Eye Res. 1976 Aug;23(2):139-48
references.pmid: 61886
references.citation: Science. 1977 Apr 29;196(4289):536-8
references.pmid: 300504
references.citation: Exp Eye Res. 1976 Aug;23(2):105-15
references.pmid: 976361
references.citation: Science. 1976 Dec 3;194(4269):1071-4
references.pmid: 982063
references.citation: Invest Ophthalmol Vis Sci. 1976 Sep;15(9):700-25
references.pmid: 986765
references.citation: J Exp Zool. 1976 Dec;198(3):287-302
references.pmid: 1003144
references.citation: Science. 1976 Dec 3;194(4269):1074-6
references.pmid: 1086510
references.citation: Exp Eye Res. 1976 Dec;23(6):637-41
references.pmid: 1087246
references.citation: J Cell Biol. 1976 Apr;69(1):29-42
references.pmid: 1254648
references.citation: J Cell Biol. 1974 Aug;62(2):257-73
references.pmid: 4139160
references.citation: J Gen Physiol. 1971 Sep;58(3):225-37
references.pmid: 4255372
references.citation: Arch Ophthalmol. 1970 Dec;84(6):810-9
references.pmid: 4321117
references.citation: Exp Eye Res. 1974 Jan;18(1):105-17
references.pmid: 4544648
references.citation: Science. 1974 Aug 2;185(4149):457-9
references.pmid: 4546260
references.citation: Annu Rev Biophys Bioeng. 1972;1:131-58
references.pmid: 4567751
references.citation: Vision Res. 1973 Apr;13(4):753-7
references.pmid: 4574738
references.citation: Exp Eye Res. 1973 Dec 24;17(6):503-10
references.pmid: 4782837
references.citation: Science. 1968 Oct 11;162(3850):230-9
references.pmid: 4877437
references.citation: J Electron Microsc (Tokyo). 1970;19(1):85-99
references.pmid: 5474310
references.citation: Fed Proc. 1971 Jan-Feb;30(1):57-63
references.pmid: 5539874
references.citation: J Cell Biol. 1968 May;37(2):424-44
references.pmid: 5656400
references.citation: Science. 1968 Aug 23;161(3843):787-9
references.pmid: 5663804
references.citation: Biochemistry. 1968 Aug;7(8):2906-13
references.pmid: 5666758
references.citation: J Cell Biol. 1968 Oct;39(1):169-84
references.pmid: 5692679
references.citation: J Cell Biol. 1969 Aug;42(2):392-403
references.pmid: 5792328
references.citation: Nature. 1969 Aug 30;223(5209):906-9
references.pmid: 5803392
references.citation: Life Sci. 1965 Oct;4(20):1981-7
references.pmid: 5864107