Co-expression of murine opsins facilitates identifying the site of cone adaptation.
Murine cones contain two opsins in the same cone, one ultraviolet (UV) and the other middle-wavelength sensitive (M). A long-wavelength flash only affecting M-opsin suppresses the cone electroretinogram (ERG) produced by light absorption of UV-cone opsin raising the hypothesis that activation of M-cone opsin suppresses UV-cone opsin responses in the same cone. Here we show that pharmacologic blockade of synaptic transmission in the superfused murine retina, which eliminates interaction from second-order neurons, fails to prevent suppression of the UV-opsin driven pathway by long-wavelength stimuli. This proves that the antagonism must be occurring in the same cone, co-expressing both opsins. Our results show that UV-opsin suppression successively ceases in presence of the M-opsin activating background light, which implies that cone light adaptation is controlled at the opsin stage, before activation of transducin. It also reveals the time course of a transient desensitization of cones due to post-opsin factors in the transduction cascade.
Ekesten
Björn
B
Department of Ophthalmology, University of Minnesota, Minneapolis 55455, USA. ekest001@umn.edu
Gouras
Peter
P
Hargitai
Janos
J
D000221:Adaptation, Ocular / Q000502:physiology*; D000818:Animals; D008027:Light; D051379:Mice; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology* / Q000528:radiation effects*; D017299:Rod Opsins / Q000378:metabolism*; D014466:Ultraviolet Rays
D017299:Rod Opsins