title: Regulation of surface expression of TRPV2 channels in the retinal pigment epithelium.
abstract: OBJECTIVE
  The retinal pigment epithelium (RPE) interacts closely with the photoreceptors in fulfilling tasks of visual function. Since an understanding of the RPE function is essential for understanding the patho-mechanisms involved in vision loss, we explored the regulation of the vanilloid receptor subtype transient receptor potential TRPV2 channels that trigger insulin-like growth factor-1 (IGF-1)-induced vascular endothelial growth factor A (VEGF-A) secretion.
  
  
  METHODS
  Immunohistochemistry was used to assess TRPV2 expression in retinal cross-sections or ARPE-19 cells, and surface expression of TRPV2 was quantified using confocal microscopy. Membrane currents of ARPE-19 cells were recorded using a whole-cell configuration of the patch-clamp technique.
  
  
  RESULTS
  TRPV2 expression was detected in the RPE of the mouse retina as well as in ARPE-19 cells. Increasing the temperature to 45 °C activated membrane conductance sensitive to SKF-96365 and ruthenium red in 60 % of cells. Preincubation with either cannabidiol (CBD) or IGF-1 led to a three- or fourfold increase in current density, respectively, in all cells, which was blocked by SKF-96365. In contrast to IGF-1, CBD stimulation of membrane conductance was further increased by heat. TRPV2 surface expression was increased by both IGF-1 and CBD, with the increase by CBD twice as large as that by IGF-1. The phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 abolished the effects on membrane conductance and surface expression.
  
  
  CONCLUSIONS
  Both CBD and IGF-1 enhance TRPV2 channel activity by specific proportions of both channel activation and PI 3-kinase-dependent surface expression: IGF-1 predominantly increases ion channel activity, whereas CBD is more active in increasing TRPV2 surface expression. Thus, differential regulation of TRPV2 surface expression is an important mechanism for modulating the responsiveness of the RPE to growth factors.
authors.affiliation: Experimental Ophthalmology, Department of Ophthalmology, Campus Virchow Clinics, Charité University Medicine Berlin, Augustenburger Platz 1, 13353, Berlin, Germany.
authors.forename: Nadine
authors.initials: N
authors.lastname: Reichhart
authors.forename: Susanne
authors.initials: S
authors.lastname: Keckeis
authors.forename: Frederik
authors.initials: F
authors.lastname: Fried
authors.forename: Gabriele
authors.initials: G
authors.lastname: Fels
authors.forename: Olaf
authors.initials: O
authors.lastname: Strauss
mesh_terms: D000818:Animals; D002185:Cannabidiol / Q000494:pharmacology; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D004553:Electric Conductivity; D006358:Hot Temperature; D006801:Humans; D007150:Immunohistochemistry; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D009025:Morpholines / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D000081082:Phosphoinositide-3 Kinase Inhibitors; D055213:Retinal Pigment Epithelium / Q000187:drug effects / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000378:metabolism*
chemical_list: D002867:Chromones; D009025:Morpholines; D000081082:Phosphoinositide-3 Kinase Inhibitors; D050916:TRPV Cation Channels; C400769:TRPV2 protein, human; D002185:Cannabidiol; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D007334:Insulin-Like Growth Factor I