title: Quantitative aspects of cGMP phosphodiesterase activation in carp rods and cones.
abstract: Cones are less light-sensitive than rods. We showed previously in carp that more light (>100-fold) is required in cones than in rods to activate 50% of cGMP phosphodiesterase (PDE). The lower effectiveness of PDE activation in carp cones is due partly to the fact that the activation rate of transducin (Tr) by light-activated visual pigment (R*) is 5-fold lower in carp cones than in rods. In this study, we tried to explain the remaining difference. First, we examined the efficiency of activation of PDE by activated Tr (Tr*). By activating PDE with known concentrations of the active (guanosine 5'-Ο-(γ-thio)triphosphate (GTPγS)-bound) form of Tr*, we found that Tr* activated PDE at a similar efficiency in rods and cones. Next, we examined the contribution of R* and Tr* lifetimes. In a comparison of PDE activation in the presence (with GTP) and absence (with GTPγS) of Tr* inactivation, PDE activation required more light (and was therefore less effective) when Tr* was inactivated in both rod and cone membranes. This is probably because inactivation of Tr* shortened its lifetime, thereby reducing the number of activated PDE molecules. The effect of Tr* inactivation was larger in cones, probably because the lifetime of Tr* is shorter in cones than in rods. The shorter lifetimes of Tr* and R* in cones seem to explain the remaining difference in the effectiveness of PDE activation between rods and cones.
authors.affiliation: From the Department of Biological Sciences, Graduate School of Science, and.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Koshitani
authors.forename: Shuji
authors.initials: S
authors.lastname: Tachibanaki
authors.forename: Satoru
authors.initials: S
authors.lastname: Kawamura
mesh_terms: D000221:Adaptation, Ocular / Q000502:physiology; D000818:Animals; D002347:Carps; D006152:Cyclic GMP / Q000378:metabolism*; D054678:Cyclic Nucleotide Phosphodiesterases, Type 2 / Q000378:metabolism*; D003623:Dark Adaptation / Q000502:physiology; D004789:Enzyme Activation / Q000502:physiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D017949:Retinal Cone Photoreceptor Cells / Q000201:enzymology* / Q000502:physiology; D017948:Retinal Rod Photoreceptor Cells / Q000201:enzymology* / Q000502:physiology; D015293:Transducin / Q000378:metabolism; D014785:Vision, Ocular / Q000502:physiology
chemical_list: D016244:Guanosine 5'-O-(3-Thiotriphosphate); D054678:Cyclic Nucleotide Phosphodiesterases, Type 2; D020962:Heterotrimeric GTP-Binding Proteins; D015293:Transducin; D006152:Cyclic GMP
keywords: Cones; Heterotrimeric G-proteins; Phosphodiesterases; Photoreceptors; Phototransduction; Retina; Rods; Transducin; cGMP Phosphodiesterase