Figure 2.

Schematic view on mechanisms assumed to contribute to Drosophila OR sensitization. A weak odor plume does not elicit an ionotropic response when ORs are in the basal state but it leads to enhanced cAMP production. This activates Orco channels causing Ca²⁺ influx into the OSN. Ca²⁺ may activate protein kinase C (PKC) and CaM, both proteins act on Orco and lead to stronger Ca²⁺ influx, i.e., there are two feedback loops. Finally the ORs become sensitized and are capable of responding to another weak odor plume with an ionotropic response which excites the receptor neuron.