Ligand-receptor interaction under periodic stimulation: a modeling study of concentration chemoreceptors

The first step of chemosensory transduction consists in the association of ligand molecules with receptor proteins borne by the cell membrane. In this article, the time evolution of ligand-receptor complexes is studied in the presence of a periodically changing ligand concentration. This type of sti mulation is a close approximation to some natural situations, for example i n olfaction. The transient and steady-state periodic levels of the complexe s, resulting from a single-step (binding) or double-step (binding and activ ation) reaction, are determined. When possible, analytical solutions are gi ven, if not for the complete model, at least for its simplified version at low ligand concentration. Otherwise, solutions are found numerically and bo th the complete and simplified versions of the model are compared. The resu lts obtained are discussed with respect to actual experimental data based o n the moth sex-pheromone receptor. Periodic steady states are achieved very quickly and their amplitude decreases when the stimulation frequency incre ases. We show that the simplified description is adequate if only a fractio n of activated receptors is sufficient to produce the maximum response, as is actually the case in the example treated. The role of the frequency of s timulation is investigated and it is shown to possess an optimal range betw een 2 and 5 Hz.