title: CaV1.3 L-type channels, maxiK Ca(2+)-dependent K(+) channels and bestrophin-1 regulate rhythmic photoreceptor outer segment phagocytosis by retinal pigment epithelial cells.
abstract: Phagocytosis of shed photoreceptor outer segments by the retinal pigment epithelium (RPE) is critical for maintenance of visual function. Because changes in intracellular Ca(2+) regulate phagocytosis, we studied in vitro the impact of different ion channels in addition to mice deficient for Cav1.3 L-type Ca(2+) channels (Ca1.3(-/-)) and maxiK Ca(2+)-dependent K(+) channels (BK(-/-)). The knockdown of Bestrophin-1 protein, a regulator of intracellular Ca(2+) homeostasis, affected phagocytosis in porcine RPE cultures. Blockage of voltage-gated L-type channels by (+)BayK8644 inhibitor reduced phagocytosis in vitro, in contrast L-type activation by (-)BayK8644 had no impact. The expression rate of Cav1.3, the predominant L-type Ca(2+) channel in RPE cells, varied at different times of day. CaV1.3(-/-) RPE lacked peak phagocytic activity following morning photoreceptor shedding in wild-type RPE and retained a higher number of phagosomes at a later time of day. The BK-channel blocker paxilline lowered phagocytosis in RPE cultures in a concentration-dependent manner. BK(-/-) RPE in vivo retained phagocytic capability but this activity, which is normally well synchronized with circadian photoreceptor shedding, shifted out of phase. Retinae of older BK(-/-) mice showed shortened photoreceptor outer segments and diminished rhodopsin content. Store-operated Ca(2+) channels Orai-1 did not affect phagocytosis in cultured RPE. TRPV channel inhibition by ruthenium-red reduced phagocytosis, whereas activation at high concentrations of 2-APB increased phagocytosis. Our data demonstrate essential roles for bestrophin-1, BK, TRPV and L-type channels in regulating retinal phagocytosis. These data indicate further the importance of BK and CaV1.3 for rhythmic phagocytic activity synchronized with photoreceptor shedding.
authors.affiliation: Experimental Ophthalmology, Eye Hospital, University Medical Center Regensburg, Franz-Josef-Strauß Allee 11, 93053 Regensburg, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Müller
authors.affiliation: Experimental Ophthalmology, Eye Hospital, University Medical Center Regensburg, Franz-Josef-Strauß Allee 11, 93053 Regensburg, Germany.
authors.forename: Néstor
authors.initials: N
authors.lastname: Más Gómez
authors.affiliation: Pharmacology, Toxicology and Clinical Pharmacy, Institute of Pharmacy, Eberhard Karls University Tübingen, Auf der Morgenstelle 8, 72076 Tübingen, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Ruth
authors.affiliation: Experimental Ophthalmology, Eye Hospital, University Medical Center Regensburg, Franz-Josef-Strauß Allee 11, 93053 Regensburg, Germany. Electronic address: olaf.strauss@charite.de.
authors.forename: Olaf
authors.initials: O
authors.lastname: Strauss
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002120:Calcium Channel Agonists / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010587:Phagocytosis / Q000187:drug effects; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000166:cytology / Q000378:metabolism; D012243:Rhodopsin / Q000378:metabolism; D013552:Swine; D050916:TRPV Cation Channels / Q000378:metabolism
chemical_list: C485995:Cacna1d protein, mouse; D002120:Calcium Channel Agonists; D020746:Calcium Channels, L-Type; D018118:Chloride Channels; D051036:Large-Conductance Calcium-Activated Potassium Channels; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D050916:TRPV Cation Channels; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D012243:Rhodopsin
keywords: BK K(+)-channel; Bestrophin-1; L-type Ca(2+)-channel; Phagocytosis; Retinal pigment epithelium