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X.-H. Wen, E. V. Olshevskaya, I. V. Peshenko, A. B. Savchenko, C. L. Makino, A. M. Dizhoor; A Role for Guanylyl Cyclase Activating Protein 1 in Setting the Size of the Single Photon Response. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1113.
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© ARVO (1962-2015); The Authors (2016-present)
Two guanylyl cyclase activating proteins, GCAP1 and GCAP2, regulate photoreceptor retinal guanylyl cyclases (retGCs) in a Ca2+ sensitive manner. To probe the role of each GCAP in phototransduction, we studied rod signaling in mice lacking GCAP1.
The mouse GUCA1A gene coding for GCAP1 was disrupted by replacing the first exon and a portion of the promoter region with a neomycin resistance cassette. GUCA1A+/- mice were bred to a homozygous state, GUCA1A-/-, which were characterized by photoreceptor gene expression, histology, electroretinography (ERG) and single cell recording.
Retinal morphology appeared to be normal in GCAP1-/- mice. GCAP1 was completely absent from retinal immunoblots and GCAP1-specific immunofluorescence was not detected in retinal sections, while GCAP2 and retGCs were present. Remarkably, total retGC activity increased over that of WT, rather than decreased. There was also a shift in K1/2 toward lower [Ca2+] compared to WT—opposite from what was previously observed in GCAP2-/- mice. Scotopic double-flash ERG responses of GCAP1-/- mice recovered quickly, as in WT. Single photon responses of GCAP1-/- rods rose for a period nearly twice as long to reach an amplitude twice as high as that of WT, but response recovery kinetics were largely normal. By comparison, the single photon response of GCAPs1&2 double knockout rods was nearly four-times larger than normal and its recovery was prolonged. Thus, GCAP1-/- rods were more sensitive and saturated at lower flash strengths compared to WT. They differed drastically from GCAP2-/- rods, whose single photon response recovered slightly more slowly but was of normal size.
GCAP1 is not crucial for normal recovery kinetics in mouse rod, but provides essential Ca2+ feedback to position its operating range by limiting the single photon response amplitude.
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