Is rhodopsin the ligand for receptor-mediated phagocytosis of rod outer segments by retinal pigment epithelium?
It has been suggested that rhodopsin may have a direct role in the attachment of shed rod outer segments (ROS) to retinal pigmented epithelial (RPE) cells initiating the events which lead to engulfment. We isolated the soluble tryptic glycopeptide from rhodopsin (GP-T1) and used it as a probe to test this hypothesis. In phagocytic assays using both cultured chick and cat RPE cells, GP-T1 did not inhibit the phagocytosis of ROS. Additionally, mannose glycoconjugates were not effective inhibitors of phagocytosis. However, glycopeptides released by tryptic digestion of intact ROS did inhibit ROS uptake by the RPE cells. The results suggest that phagocytosis of ROS is not mediated through a simple carbohydrate recognition system and that rhodopsin is not the ligand recognized by RPE cells.
Philp
N J
NJ
Department of Anatomy, School of Medicine, University of Pennsylvania, Philadelphia 19104.
Nachmias
V T
VT
Lee
D
D
Stramm
L
L
Buzdygon
B
B
D000818:Animals; D002415:Cats; D002478:Cells, Cultured; D002642:Chick Embryo; D006020:Glycopeptides / Q000302:isolation & purification / Q000494:pharmacology; D008024:Ligands; D008351:Mannans / Q000494:pharmacology; D008358:Mannose / Q000494:pharmacology; D010587:Phagocytosis / Q000187:drug effects; D010786:Photoreceptor Cells / Q000378:metabolism*; D010857:Pigment Epithelium of Eye / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000502:physiology; D012168:Retinal Pigments / Q000502:physiology*; D012243:Rhodopsin / Q000502:physiology*; D012374:Rod Cell Outer Segment / Q000378:metabolism*; D012709:Serum Albumin; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology
D006020:Glycopeptides; D008024:Ligands; D008351:Mannans; D011956:Receptors, Cell Surface; D012168:Retinal Pigments; D012709:Serum Albumin; C055000:glycopeptide T1; C023840:mannose-bovine serum albumin conjugate; D012710:Serum Albumin, Bovine; D012243:Rhodopsin; D014357:Trypsin; D008358:Mannose