Profoundly different calcium permeation and blockage determine the specific function of distinct cyclic nucleotide-gated channels.
Sensory transduction in vertebrate photoreceptors and olfactory sensory neurons is mediated by cyclic nucleotide-gated (CNG) channels that conduct mono- and divalent cations. Ca2+ entering the cell through CNG channels intimately controls signaling pathways by regulating several key enzymes. Cloned CNG channels from photoreceptors and olfactory sensory neurons profoundly differ in their relative Ca2+ permeability, their blockage by external divalent cations, and the fraction of current carried by Ca2+. In particular, CNG channels from cone photoreceptors conduct significantly more Ca2+ than those from rod photoreceptors. Furthermore, the current through the olfactory CNG channel is entirely carried by Ca2+ at approximately 3 mM extracellular Ca2+. These results suggest that a major function of CNG channels is to provide a pathway for Ca2+ entry.
Frings
S
S
Institut für Biologische Informationsverarbeitung, Forschungszentrum Jülich, Federal Republic of Germany.
Seifert
R
R
Godde
M
M
Kaupp
U B
UB
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002417:Cattle; D002463:Cell Membrane Permeability / Q000502:physiology; D054815:Cyclic Nucleotide-Gated Cation Channels; D015640:Ion Channel Gating / Q000502:physiology*; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D009712:Nucleotides, Cyclic / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D017948:Retinal Rod Photoreceptor Cells / Q000648:ultrastructure; D014981:Xenopus
D002121:Calcium Channel Blockers; D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels; D009712:Nucleotides, Cyclic; D008274:Magnesium; D002118:Calcium