Dose-response relationships in an olfactory flux detector model revisited

A simple model of an odorant flux detector including odorant uptake, activation of odorant receptor molecules and enzymatic odorant deactivation can produce different types of static dose–response relationships. Depending on the binding character-istics of the odorant to the receptor molecule and to the deactivating enzyme, the receptor occupation by the odorant as related to the odorant uptake is quasi-hyperbolic, linear or, close to saturation, steeper than linear. In Rospars et al. (2003, Chem. Senses, 28: 509–522) a note contributed by both of us stated erroneously that an equation describing these relation-ships given previously (Kaissling, 1998, Chem. Senses, 23; 99–111; Kaissling, 2001, Chem. Senses, 26: 125–150) was incorrect. We show here that the difference in equations was due to a simplifying assumption in Rospars et al. (2003) about the deacti-vating enzyme, we summarize briefly the properties of the correct equation of Kaissling (1998, 2001) and we discuss the rela-tion with the model studied in Rospars et al. (2003). Key words: chemoreceptors, dose–response relationships, flux detectors, odorant deactivation, pulsed odorant stimulation, receptor occupation modeling Model of a flux detector Olfactory organs which adsorb from the air space but do not desorb odorant molecules need a mechanism for odorant deactivation in order to avoid accumulation of active stim-ulus molecules at the receptor cells. Here, we consider a network of chemical reactions including the uptake of the odorant or ligand L, its reversible binding to a receptor R, the reversible change of the complex LR to an activated state LR ′ (Minor and Kaissling, 2003), a reversible binding of L to a hypothetical deactivating enzyme N, and an irreversible odorant deactivation by changing of the complex LN to P