Molecular reaction cascades in olfactory signal transduction

Odorant induced second messenger signals in ciliary preparations from rat olfactory epithelia were monitored in the subsecond time range using a rapid kinetic methodology. Application of micromolar concentrations of odorants induced a rapid and transient elevation of second messenger concentrations. The odorous compounds analyzed induced in a mutually exclusive way the formation of either cyclic adenosine monophosphate or inositol-triphosphate. The activating effects of odorants on intracellular signalling cascades appear to be mediated via different G-proteins. Thus, at least two different second messenger pathways appear to be involved in olfactory signal transduction. Selective inhibition of odor-induced second messenger responses by certain lectins indicate that glycoproteins appear to be involved in the perception or transduction of olfactory signals. In the presence of protein kinase inhibitors the odorant-induced second messenger response is no longer transient but persistent over a longer time period, suggesting that termination of the signal is realized via feedback phosphorylation of functional elements in the reaction cascade.