Identification of competitive antagonists of the rod photoreceptor cGMP-gated cation channel: β-phenyl-1,N2-etheno-substituted cGMP analogues as probes of the cGMP-binding site

Ji Ye Wei, Ethan D. Cohen, Yang Yan Yan, Hans G. Genieser, Colin J. Barnstable

Research output: Contribution to journalArticle

37 Scopus citations

Abstract

cGMP is the natural activator of the cyclic nucleotide-gated channel originally isolated from rod photoreceptors but now known to be expressed in a wide variety of neural and non-neural cells. To identify antagonists of cGMP action and to better understand the interaction between cGMP and the channel protein, experimental studies were undertaken using four synthetic cGMP analogues, PET-cGMP, 8-Br-PET-cGMP, Rp-8-Br-PET-cGMPS, and Sp-8-Br-PET-cGMPS. With excised patches from either Xenopus oocytes expressing a cloned rat rod channel α-subunit or from native Xenopus rod photoreceptors, Rp-8-Br-PET-cGMPS competitively suppressed the cGMP-induced current with an IC50 of 25 μM and Sp-8-Br-PET-cGMPS inhibited this current with an IC50 of 105 μM. On the expressed rat rod channel, 8-Br-PET-cGMP behaved as a very weak partial agonist at high concentrations and an antagonist (IC50 = 64 μM) at lower concentrations when coapplied with cGMP. PET-cGMP did not activate channel currents alone but showed synergism when coapplied with subsaturating concentrations of cGMP. Because Sp-8-Br-PET-cGMPS is a potent activator of type I cGMP-dependent protein kinase, but a competitive antagonist of channel activation, it will be a useful reagent for discriminating between those effects of cGMP that are mediated by a protein kinase and those mediated by channel activation. Because the PET derivatives all contain a phenyl-substituted 5-membered ring system fused to the amino group in position 2 and the nitrogen in position 1 of the guanine ring, the results support the idea that N1 and N2 are important for channel activation. They also suggest a minor role for the cyclic phosphate group in binding or activation.

Original languageEnglish (US)
Pages (from-to)16815-16823
Number of pages9
JournalBiochemistry
Volume35
Issue number51
StatePublished - Dec 24 1996

All Science Journal Classification (ASJC) codes

  • Biochemistry

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