Co-expression of wild-type and mutant olfactory cyclic nucleotide-gated channels: restoration of the native sensitivity to Ca2+ and Mg2+ blockage

In the pore of homomeric cyclic nucleotide-gated (CNG) channels, Ca2+ and M g2+ bind to a set of glutamate residues, which in the bovine olfactory CNG channel are located at position 340, However, native CNG channels from olfa ctory sensory neurons are composed by the assembly of three different types of subunits, each having a different residue - glutamate, aspartate or gly cine - at the position corresponding to the binding site for external Ca2and Mg2+. We co-expressed the wild-type principal a subunit with its mutant s E340G and E340D in different combinations in Xenopus laevis oocytes, and measured Ca2+ and Mg2+ blockage in excised outside-out membrane patches. Th e comparison between our results and data from native olfactory CNG channel s indicates that the presence of all three residues - glutamate, aspartate and glycine - in the different subunits, is necessary to restore the sensit ivity to external Ca2+ and Mg2+ measured in native channels. NeuroReport 12 :2363-2367 (C) 2001 Lippincott Williams & Wilkins.