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 c onfiguration of the patch-clamp technique in both recombinant wild-type alp ha -homomeric rat olfactory adenosine 3',5'-cyclic monophosphate (cAMP)-gat ed channels (rOCNCl) expressed in human embryonic kidney cells (HEK 293) an d native cyclic nucleotide-gated (CNG) channels in acutely isolated rat olf actory receptor neurons. Single-channel and macroscopic currents were activ ated by 200 muM and 500 muM cAMP, respecitively. Macroscopic currents, meas ured with mixtures of Na+-NH4+ or Cs+-Li+ in the cytoplasmic bathing soluti on, displayed AMFE in the rOCNCl channels at both positive and negative mem brane potentials. The rOCNCl single-channel conductance showed a distinct m inimum (or maximum) in an 80% Na+-20% NH4+ mixture (or a 60% Cs+-40% Li+ mi xture), but only at positive membrane potentials. Macroscopic measurements in native olfactory CNG channels with mixtures of Na+-NH4+ indicated simila r AMFE. These results suggest that both native CNG channels and recombinant alpha -homomeric channels allows several ions to be present simultaneously within the channel pore. The also further validate the dominant role of th e alpha -subunit in permeation through these channels, provide the first ev idence to suggest that rOCNCl channels have multi-ion properties and furthe r justify the use of the rOCNCl channel as an effective model for structure -function studies of ion permeation and selectivity in olfactory CNG channe ls.