Bestrophin is not a Chloride Channel.

Abstract

Abstract: : Purpose:The VMD2 gene which is mutated in Best macular dystrophy encodes bestrophin. It has been proposed that bestrophin functions as a Ca2+ sensitive Cl channel. Our studies were intended to evaluate this hypothesis using in vitro and in vivo approaches. Methods: RPE–J and HEK–293 cells were transfected with bestrophin or bestrophin fused with GFP. Cl currents were recorded from transfected cells using patch clamp. Bestrophin stoichiometry was determined by velocity sedimentation and gel filtration. Bestrophin was localized by fluorescence microscopy. Adenovirus–mediated gene transfer was used to express bestrophin in the RPE of adult Long–Evans rats. Two weeks after subretinal injection the light peak was assessed by DC–ERG. Results: Significant Cl currents were not detected in either RPE–J or HEK–293 cells transfected with bestrophin or bestrophin–GFP. A sub–population of cells overexpressing bestrophin and in which the protein was predominantly in intracellular compartments exhibited mean currents which were highly variable but not significantly different from controls. Bestrophin solubilized from pig RPE was determined to be dimeric, unlike that from transfected cells, which formed higher order aggregates. Rats overexpressing bestrophin exhibited a shift in light peak luminance response function, but no significant change in the range of the response. Conclusions: We did not find evidence to support a role for bestrophin as a Ca2+ dependent Cl channel.

Keywords: electroretinography: non–clinical • ion channels • retinal pigment epithelium