抄録
It is now fairly well established that olfactory signal transduction is mediated by cytoplasmic cAMP. Up to this point, however, dynamics of cytoplasmic cAMP has been still a matter of speculation. This is mainly because that olfactory cilia have very fine structure which has limited applicable experimental protocols. In the present work, we used caged substances to estimate the dynamics of cytoplasmic cAMP, while the membrane response was monitored by whole-cell recording method. Experiments were carried out in the presence and the absence of Ca influx which causes drastic changes in the waveform of the current responses. Mainly, it is known that Ca ion has two effects on the olfactory system; feedback to the CNG channel and opening of Cl channel.Through the experiments using brief pulses of UV light, intensity-response relations were found to be fitted by the Hill equation with high cooperatively (Hill coefficient, n, of 5) in the presence, and with low cooperativity (n=2) in the absence of Ca influx. The rising phase of the current was fitted also by the Hill equation with n of 5. From such observation, it was expected that the current developing phase represents the time course for the [cAMP]i increase. To support this idea, the time course of the rising phase became less steep when the Ca influx is removed. It is therefore likely that [cAMP]i increases almost linearly with time. Also, the present work reconfirmed a classical concept that Ca ion contributes to signal amplification in olfactory signal transduction. [Jpn J Physiol 54 Suppl:S177 (2004)]
