Gating of heteromeric retinal rod channels by cyclic AMP: role of the C-terminal and pore domains.

Cyclic nucleotide-gated channels are tetramers composed of homologous alpha and beta subunits. C-terminal truncation mutants of the alpha and beta subunits of the retinal rod channel were expressed in Xenopus oocytes, and analyzed for cGMP- and cAMP-induced currents (single-channel records and macroscopic currents). When the alpha subunit truncated downstream of the cGMP-binding site (alpha D608stop) is co-injected with truncated beta subunits, the heteromeric channels present a drastic increase of cAMP sensitivity.