Noise analysis of ion channels in non-space-clamped cables: Estimates of channel parameters in olfactory cilia

Ion channels in the cilia of olfactory neurons are part of the transduction machinery of olfaction. Odorant stimuli have been shown to induce a biphasic current response, consisting of a cAMP-activated current and a Ca²⁺ -activated CI current. We have developed a noise analysis method to study ion channels in leaky cables, such as the olfactory cilium, under non-space-clamp conditions. We performed steady-state noise analysis on ligand-induced currents in excised cilia, voltage-clamped at input and internally perfused with cAMP or Ca²⁺. The cAMP-activated channels analyzed by this method gave results similar to those of single-channel recordings (γ = 8.3 pS). Single-channel currents have not yet been recorded for the Ca²⁺- activated CI channels. Using our noise analysis method, we estimate a unit conductance, γ = 0.8 pS, for these channels. The density of channels was found to be ~70 channels/μm² for both channel species.