Phosducin regulates the expression of transducin betagamma subunits in rod photoreceptors and does not contribute to phototransduction adaptation.
For over a decade, phosducin's interaction with the betagamma subunits of the G protein, transducin, has been thought to contribute to light adaptation by dynamically controlling the amount of transducin heterotrimer available for activation by photoexcited rhodopsin. In this study we directly tested this hypothesis by characterizing the dark- and light-adapted response properties of phosducin knockout (Pd- / -) rods. Pd- / - rods were notably less sensitive to light than wild-type (WT) rods. The gain of transduction, as measured by the amplification constant using the Lamb-Pugh model of activation, was 32% lower in Pd- / - rods than in WT rods. This reduced amplification correlated with a 36% reduction in the level of transducin betagamma-subunit expression, and thus available heterotrimer in Pd- / - rods. However, commonly studied forms of light adaptation were normal in the absence of phosducin. Thus, phosducin does not appear to contribute to adaptation mechanisms of the outer segment by dynamically controlling heterotrimer availability, but rather is necessary for maintaining normal transducin expression and therefore normal flash sensitivity in rods.
Krispel
Claudia M
CM
Center for Neuroscience and Department of Ophthamology and Vision Science, University of California, Davis, CA 95618, USA.
Sokolov
Maxim
M
Chen
Yen-Ming
YM
Song
Hongman
H
Herrmann
Rolf
R
Arshavsky
Vadim Y
VY
Burns
Marie E
ME
D000221:Adaptation, Ocular; D000818:Animals; D003623:Dark Adaptation; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D020555:GTP-Binding Protein Regulators / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D044385:GTP-Binding Protein alpha Subunits; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D008564:Membrane Potentials; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010750:Phosphoproteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D021122:Protein Subunits; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*; D013997:Time Factors; D015293:Transducin; D014785:Vision, Ocular
D005136:Eye Proteins; D020555:GTP-Binding Protein Regulators; D044385:GTP-Binding Protein alpha Subunits; C488949:Gnat1 protein, mouse; D010750:Phosphoproteins; D021122:Protein Subunits; C065631:phosducin; D020962:Heterotrimeric GTP-Binding Proteins; D015293:Transducin