Abstract
Olfactory reception is unique in that the transduction current is generated by two types of ion channels; cyclic nucleotide-gated (CNG) channels and calcium-activated chloride (Cl(Ca)) channels in the nano-scale sensory cilia. Because of such sequential cascade in the nano-tube structure, quantification of individual channels is still limited. For long period of time, free manipulation of cytoplasmic factors in the cilia has been thought to be a technical limitation. However, recent achievements using caged compound have provided possibilities of overcoming these technical difficulties. In this work, we focused on manipulating the [Ca2+]i in the nano-tube cilia and on quantification of Cl(Ca) channels, by comparing with the odorant and caged cAMP responses. Such experiments enable us to examine the role of molecular elements in the sequential cascade step by step. We loaded the cilia with caged Ca (DM-Nitrophen) under whole-cell patch clamping, monitoring the Cl(Ca) current as an index of [Ca2+]i increase. Basic physiological properties of Cl(Ca) channels were examined; I-V curve, reversal potentials, [Cl]o dependence and dose-response relation showing non-linearity. The properties were consistent with the idea that the Cl current is included in the odorant- and cAMP-induced responses. Besides, adaptation and odorant-suppression that have been observed in the odorant- and cAMP-induced current were less observed in this current. We propose that Cl(Ca) channel is important for the non-linear amplification of the system and that the adaptation and suppression of the responses are controlled at the level of the CNG channel. [J Physiol Sci. 2008;58 Suppl:S166]
