Extracellular proton alters the divalent cation binding affinity in a cyclic nucleotide-gated channel pore.
Extracellular protons in the range of 10(-9) to 10(-5) M effectively suppressed Na+ current (K(1/2) = 10(-6.1)) through the bovine retinal guanosine 3',5'-cyclic mononucleotide-gated ion channel expressed in Xenopus oocytes. The reduction of channel current was mediated by a single glutamate residue (Glu363) within the pore-forming region of the channel, also involved in extracellular divalent cation binding. Increasing the concentration of extracellular proton decreased the binding affinity of the extracellular divalent cation (e.g. Sr2+) and the large difference of binding affinity previously observed between the wild-type and E363D mutant channel disappeared. These results indicate that the permeation characteristics of cyclic nucleotide-gated ion channel can be altered by extracellular pH through a single acidic residue in the channel conduction pathway.
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Department of Life Science, Kwangju Institute of Science and Technology, South Korea.
Park
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D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D002413:Cations, Divalent / Q000378:metabolism*; D002417:Cattle; D054815:Cyclic Nucleotide-Gated Cation Channels; D004594:Electrophysiology; D018698:Glutamic Acid; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000378:metabolism*; D009154:Mutation; D009865:Oocytes; D011522:Protons; D012964:Sodium / Q000378:metabolism; D055672:Static Electricity; D013324:Strontium / Q000378:metabolism; D017186:Titrimetry; D014982:Xenopus laevis
D002413:Cations, Divalent; D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels; D011522:Protons; D018698:Glutamic Acid; D012964:Sodium; D013324:Strontium