Anomalous mole-fraction effects in recombinant and native cyclic nucleotide-gated channels in rat olfactory receptor neurons.
Anomalous mole-fraction effects (AMFE) were studied, using the inside-out configuration of the patchclamp technique, in both recombinant wild-type alpha-homomeric rat olfactory adenosine 3',5'-cyclic monophosphate (cAMP)-gated channels (rOCNC1) expressed in human embryonic kidney cells (HEK 293) and native cyclic nucleotide-gated (CNG) channels in acutely isolated rat olfactory receptor neurons. Single-channel and macroscopic currents were activated by 200 microM and 500 microM cAMP, respectively. Macroscopic currents, measured with mixtures of Na(+)-NH(4)(+) or Cs(+)-Li(+) in the cytoplasmic bathing solution, displayed AMFE in the rOCNC1 channels at both positive and negative membrane potentials. The rOCNC1 single-channel conductance showed a distinct minimum (or maximum) in an 80% Na(+)-20% NH(4)(+) mixture (or a 60% Cs(+)-40% Li(+) mixture), but only at positive membrane potentials. Macroscopic measurements in native olfactory CNG channels with mixtures of Na(+)-NH(4)(+) indicated similar AMFE. These results suggest that both native CNG channels and recombinant alpha-homomeric channels allow several ions to be present simultaneously within the channel pore. They also further validate the dominant role of the alpha-subunit in permeation through these channels, provide the first evidence to suggest that rOCNC1 channels have multi-ion properties and further justify the use of the rOCNC1 channel as an effective model for structure-function studies of ion permeation and selectivity in olfactory CNG channels.
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W
W
Schools of Physiology and Pharmacology, The University of New South Wales, Sydney 2052, Australia.
Moorhouse
A J
AJ
Cunningham
A M
AM
Barry
P H
PH
D000818:Animals; D002460:Cell Line; D054815:Cyclic Nucleotide-Gated Cation Channels; D005260:Female; D006801:Humans; D015640:Ion Channel Gating; D007473:Ion Channels / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D009833:Olfactory Pathways / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins
D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels; D011994:Recombinant Proteins