Perireceptor and receptor events in olfaction. Comparison of concentration and flux detectors: a modeling study.
Transduction in chemosensory cells begins with the association of ligand molecules to receptor proteins borne by the cell membrane. The receptor-ligand complexes formed act as signaling compounds that trigger a G-protein cascade. This receptor-ligand interaction, described here by a single-step or double-step reaction, depends on factors controlling the access of the ligand molecules to the cell membrane. Two basic mechanisms can be distinguished: concentration detectors (CD), in which the ligand can freely diffuse to the membrane, and flux detectors (FD), in which it accumulates irreversibly in a distinct perireceptor space where it is chemically deactivated. These two systems, plus their generalization, are investigated and compared. The transient and steady-state numbers of complexes are studied as a function of the external ligand concentration. The biological significance of the results is shown in a well-studied example of FD, the insect sex-pheromone olfactory receptor neuron. How the number of complexes can code for the intensity of stimulation is analyzed using the size, dynamic range and sensitivity of the steady-state responses, and the time needed to reach a predefined level of the transient responses. It is shown that the FD design affords a large increase in sensitivity (a shift of the threshold response towards low concentration) with respect to the CD design, which is paid for by a lesser ability to follow fast changes in stimulus intensity.
Rospars
J P
JP
Unité de Biométrie, INRA, 78026 Versailles Cedex, France.
Krivan
V
V
Lánský
P
P
D007700:Kinetics; D008954:Models, Biological; D009812:Odorants; D009833:Olfactory Pathways / Q000502:physiology*; D012903:Smell / Q000502:physiology*