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Y-W Peng, Y Hao, K Oka, F Wong; Light-induced Changes of PKC Alpha Immunoreactivity in Rod Bipolar Cells of Normal and RD Mice . Invest. Ophthalmol. Vis. Sci. 2002;43(13):741.
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Purpose: In the retina, protein kinase C alpha-immunoreactivity (PKCa-ir) identifies mainly rod bipolar cells. Rod bipolar cells are interneurons that relate visual input from rod photoreceptors to the visual pathway, although the function and regulation of PKCa in this signaling process are poorly understood. Commercially available monoclonal antibodies recognize different epitopes in PKCa. Without specifying a precise mechanistic model, we tested the hypothesis that PKCa function is associated with alterations in the epitopes such that light-induced changes of PKCa-ir in rod bipolar cells may be detected by monoclonal antibodies. Methods: Normal and retinal degeneration (rd) mice (18-days-old) were kept in total darkness for at least 24 h before exposing to room light for 30 min to 7 h at different times during the day. Immunocytochemical and protein blot analyses were performed on the retinas using Ab-2 (Oncogene) and SC8393 (Santa Cruz) monoclonal antibodies. Results: In dark-adapted animals, both antibodies identified PKCa-immunoreactive rod bipolar cells. In animals subsequently exposed to light, only SC8393 yielded PKCa-ir, although protein blot analysis identified normal levels of retinal PKCa and without significant proteolysis. Substantial reduction in PKCa-ir to Ab-2 was observable after 30 min, while virtual elimination of the signal required at least 1 h of light exposure. Conclusion: (1) Visual signals transmitted synaptically from rods to rod bipolar cells regulate PKCa directly or indirectly. Although still obscure, the mechanisms of regulation likely involve physical alterations in the region of the PKCa protein recognized by Ab-2. (2) In the virtual absence of rods in 18-day-old rd retinas, cone terminals formed synapses with rod bipolar cell dendrites. Demonstration of light-induced changes of PKCa-ir in rod bipolar cells of the rd retina strongly suggested that these ectopic synapses were functional.
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