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Replacing the rod with the cone transducin α subunit decreases sensitivity and accelerates response decay
Author(s) -
Chen C.K.,
Woodruff M. L.,
Chen F. S.,
Shim H.,
Cilluffo M. C.,
Fain G. L.
Publication year - 2010
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2010.191221
Subject(s) - transducin , rhodopsin , biophysics , protein subunit , visual phototransduction , kinetics , chemistry , rod , biology , microbiology and biotechnology , biochemistry , retinal , physics , medicine , quantum mechanics , gene , alternative medicine , pathology
Cone vision is less sensitive than rod vision. Much of this difference can be attributed to the photoreceptors themselves, but the reason why the cones are less sensitive is still unknown. Recent recordings indicate that one important factor may be a difference in the rate of activation of cone transduction; that is, the rising phase of the cone response per bleached rhodopsin molecule (Rh*) has a smaller slope than the rising phase of the rod response per Rh*, perhaps because some step between Rh* and activation of the phosphodiesterase 6 (PDE6) effector molecule occurs with less gain. Since rods and cones have different G‐protein α subunits, and since this subunit (Tα) plays a key role both in the interaction of G‐protein with Rh* and the activation of PDE6, we investigated the mechanism of the amplification difference by expressing cone Tα in rod Tα‐knockout rods to produce so‐called GNAT2C mice. We show that rods in GNAT2C mice have decreased sensitivity and a rate of activation half that of wild‐type (WT) mouse rods. Furthermore, GNAT2C responses recover more rapidly than WT responses with kinetic parameters resembling those of native mouse cones. Our results show for the first time that part of the difference in sensitivity and response kinetics between rods and cones may be the result of a difference in the G‐protein α subunit. They also indicate more generally that the molecular nature of G‐protein α may play an important role in the kinetics of G‐protein cascades for metabotropic receptors throughout the body.