Substituted cGMP analogs can act as selective agonists of the rod photoreceptor cGMP-gated cation channel.
Cyclic nucleotide-gated (CNG) channels are expressed in many cell types in both the nervous system and nonexcitable tissues. In order to understand the roles of cGMP-gated channels, and to distinguish actions of cGMP mediated through CNG channels from those through cGMP-dependent protein kinase (G-kinase), several new cGMP analogs were tested for potency as CNG channel agonists. Using Xenopus oocytes expressing the rat rod cGMP-gated ion channel alpha-subunit, we showed that an analog containing a pCPT group at the 8-position, 8-pCPT-cGMP, was 80 times more potent than cGMP and 14 times more potent than 8-Br-cGMP. 8-pCPT-cGMP is the most potent CNG channel agonist so far described and also has the advantages of much better membrane permeability as well as much higher resistance to PDE-hydrolysis, as compared with 8-Br-cGMP. Modification of both 8-Br-cGMP and 8-pCPT-cGMP by introduction of a sulphur atom into the cyclic phosphate group gave smaller changes in agonist efficiency. Both Sp-8-Br-cGMPS and Sp-8-pCPT-cGMPS acted as agonists of CNG channels and are also G-kinase activators. In contrast, Rp-8-Br-cGMPS was a channel agonist, with an EC50 of 173.5 microM, but a G-kinase antagonist with a Ki of 4 microM. Finally, Rp-8-pCPT-cGMPS was a channel agonist and showed additional noncompetitive antagonist activity at higher concentrations. The results suggest that 8-pCPT-cGMPS is a highly potent photoreceptor CNG channel agonist with high membrane permeability and PDE-resistance and furthermore Rp-8-Br-cGMPS can be used to test whether the actions of cGMP are selectively mediated by CNG channels.
Wei
J Y
JY
Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, CT 06520-8061, USA.
Cohen
E D
ED
Genieser
H G
HG
Barnstable
C J
CJ
D000818:Animals; D006152:Cyclic GMP / Q000819:agonists* / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels / Q000819:agonists*; D009865:Oocytes; D010786:Photoreceptor Cells / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D012374:Rod Cell Outer Segment / Q000187:drug effects / Q000378:metabolism; D013873:Thionucleotides / Q000494:pharmacology; D014981:Xenopus
C090860:8-(4-chlorophenylthio)guanosine 3',5'-cyclic monophosphorothioate; D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels; D013873:Thionucleotides; C055656:8-((4-chlorophenyl)thio)cyclic-3',5'-GMP; D006152:Cyclic GMP