Ca2+ modulates an unspecific cation conductance in olfactory cilia of Xenopus laevis

Summary Olfactory neurones of Xenopus laevis were studied by the patch clamp technique under voltage-clamp conditions. Isolated receptor cells were obtained by dissociating the olfactory mucosa in a Ca²⁺-free solution. Usually some of the resulting isolated olfactory cells lost all of their cilia during the dissociation procedure. Comparing the currents of cells with cilia to those of cells without cilia, a marked difference was found. When all known voltage-gated currents except the Ca²⁺-current were blocked, cells without cilia showed the voltage-gated Ca²⁺-current alone whereas cells with cilia clearly had an additional conductance g_c. It could be activated in two ways, either by Ca²⁺ entry through Ca²⁺-channels or by Ca²⁺ entry through the Na/Ca-exchanger working in the reversed mode at positive membrane potentials. This ciliar conductance g_c had its reversal potential at 0 mV. Replacing extracellular Cl^- by isethionate on the one hand, and Na⁺ by Cs⁺ or N-methyl-D-glucamine on the other showed that g_c was permeable for cations but not for Cl^-. In conclusion, there appears to be a Ca²⁺-dependent unselective cation conductance on the cilia of olfactory neurones. The probable role of g_c as the last step in an IP₃/Ca mediated transduction path-way is suggested.