Quantitative mapping of ion channel regulation by visual cycle activity in rodent photoreceptors in vivo.
OBJECTIVE
To test the hypothesis that the extent of outer retina uptake of manganese, measured noninvasively with manganese-enhanced MRI (MEMRI), is a quantitative biomarker of photoreceptor ion channel regulation by visual cycle activity.


METHODS
Four groups of animals were studied: control rats adapted to three different background light intensities, dark-adapted control mice systemically pretreated with retinylamine, and dark-adapted mice with a nonsense mutation in exon 3 of the RPE65 gene (RPE65(rd12)) with and without systemic 11-cis-retinal pretreatment. In all cases, rodents were anesthetized and studied with MEMRI 4 hours after manganese administration IP. Central retinal thickness and intraretinal ion channel regulation were measured from the MEMRI data.


RESULTS
No differences (P>0.05) in retinal thickness were noted within any arm of this study. In rats, manganese uptake was inversely proportional to the background light intensity in the outer retina but not in the inner retina. Specific inhibition at the level of RPE65 activity, either acutely with retinylamine or chronically in RPE65(rd12) mice, similarly reduced (P<0.05) outer retinal manganese uptake compared with that in control mice. In RPE65(rd12) mice, outer retinal manganese uptake returned to normal (P>0.05) after 11-cis retinal treatment. Inner retinal uptake was supernormal (P<0.05) in retinylamine-treated mice but normal in untreated or 11-cis treated RPE65(rd12) mice.


CONCLUSIONS
The present data support measuring the extent of manganese uptake in the outer retina as an analytic noninvasive metric of visual cycle regulation of photoreceptor ion channel activity in vivo.
Berkowitz
Bruce A
BA
Department of Anatomy and Cell Biology, Wayne State University, Detroit, Michigan 48201, USA. baberko@med.wayne.edu
Roberts
Robin
R
Oleske
Deanna A
DA
Chang
Myungwon
M
Schafer
Stephen
S
Bissig
David
D
Gradianu
Marius
M
D000221:Adaptation, Ocular / Q000502:physiology; D000818:Animals; D015415:Biomarkers / Q000378:metabolism*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D003623:Dark Adaptation; D004224:Diterpenes / Q000494:pharmacology; D005136:Eye Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism*; D008027:Light; D008279:Magnetic Resonance Imaging; D008297:Male; D008345:Manganese / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism* / Q000528:radiation effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D014785:Vision, Ocular / Q000502:physiology*; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase
D015415:Biomarkers; D002352:Carrier Proteins; D004224:Diterpenes; D005136:Eye Proteins; D007473:Ion Channels; D008345:Manganese; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase; C009167:retinylamine