Downregulation of cGMP phosphodiesterase induced by expression of GTPase-deficient cone transducin in mouse rod photoreceptors.
OBJECTIVE
Photoexcitation of vertebrate retinal rod photoreceptors stimulates GTP binding to the transducin alpha subunit. Like other GTP-binding proteins, transducin restores itself to an inactive form by hydrolyzing its bound GTP. The role of GTP hydrolysis in phototransduction was investigated.


METHODS
A mutant form of cone transducin alpha deficient in its ability to hydrolyze bound GTP was expressed in mouse rod photoreceptors.


RESULTS
Expression of the mutant cone transducin alpha at levels threefold to sixfold higher than endogenous rod transducin alpha led to a specific depletion of the transducin target, cGMP phosphodiesterase, and a decrease in the cGMP level. Suction electrode recordings revealed abnormally prolonged flash responses, decreased maximal response amplitudes, and a shift in the stimulus-response relation to higher flash strengths.


CONCLUSIONS
Rods expressing high levels of GTPase-deficient cone transduction alpha have reduced levels of phosphodiesterase catalytic subunits and cGMP. These changes are associated with prolonged flash responses, reduced dark current, and decreased sensitivity to light.
Raport
C J
CJ
Department of Biochemistry and Howard Hughes Medical Institute, Seattle, Washington 98195.
Lem
J
J
Makino
C
C
Chen
C K
CK
Fitch
C L
CL
Hobson
A
A
Baylor
D
D
Simon
M I
MI
Hurley
J B
JB
D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D006152:Cyclic GMP / Q000378:metabolism; D015536:Down-Regulation; D020558:GTP Phosphohydrolases / Q000172:deficiency*; D015870:Gene Expression; D006160:Guanosine Triphosphate / Q000502:physiology; D006868:Hydrolysis; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D017354:Point Mutation; D017949:Retinal Cone Photoreceptor Cells / Q000201:enzymology; D017948:Retinal Rod Photoreceptor Cells / Q000201:enzymology*; D015398:Signal Transduction / Q000502:physiology; D015293:Transducin / Q000235:genetics / Q000378:metabolism*
D006160:Guanosine Triphosphate; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D020558:GTP Phosphohydrolases; D015293:Transducin; D006152:Cyclic GMP