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 transdu ction machinery of olfaction. Odorant stimuli have been shown to induc e a biphasic current response, consisting of a cAMP-activated current and a Ca2+-activated Cl- current. We have developed a noise analysis m ethod to study ion channels in leaky cables, such as the olfactory cil ium, 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-activate d channels analyzed by this method gave results similar to those of si ngle-channel recordings (gamma = 8.3 pS). Single-channel currents have not yet been recorded for the Ca2+-activated Cl- channels. Using our noise analysis method, we estimate a unit conductance, gamma = 0.8 pS, for these channels. The density of channels was found to be similar t o 70 channels/mu m(2) for both channel species.