Mechanisms Determining the Dynamic Range of the Bullfrog Olfactory Receptor Cell

• Published in: Journal of neurophysiology 2005-04, Vol.93 (4), p.1880-1888
• Main Authors: Tomaru, Akihiro, Kurahashi, Takashi
• Format: Article
• Language: English
• Subjects: Action Potentials - physiology; Animals; In Vitro Techniques; Olfactory Mucosa - physiology; Olfactory Receptor Neurons - physiology; Rana catesbeiana - physiology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.00303.2004

1 Department of Biophysical Engineering, Graduate School of Engineering Science; and 2 Department of Frontier Biosciences, Osaka University, Toyonaka, Osaka, Japan Submitted 5 April 2004; accepted in final form 9 November 2004 Spike discharges of single olfactory receptor cells (ORCs) were recorded with the whole cell patch-clamp method applied to slice preparation. In parallel, activities of transduction channels were measured under the voltage-clamp condition. When cells were stimulated by odorants, 54 out of 306 cells exhibited inward current responses (10 mM cineole in the puffer pipette). The amplitude of the inward current was dependent on the stimulus period, reflecting the time integration for the stimulus dose, and the relation could be fitted by the Hill equation. Under the current-clamp condition, current injection induced spike discharges. In cells showing repetitive firings, the firing frequency was dependent on the amount of injected current. The relation was fitted by the Michaelis-Menten equation showing saturation. When cells were responsive to the odorant and had abilities to discharge repetitive spikes, the depolarizing responses were accompanied by repetitive spikes. In those cells, the spike frequency was dose-dependent, expressing saturation similar to the result obtained by current injection. Since both transduction channel and spike generative steps expressed saturation in their dose dependences, we explored what step(s) actually determines saturation in ORC signaling processes. By examining dose-response relations of both the current and spikes in the same cells, saturating dose was found to be dependent largely on that of the transduction step. This suggests that the dynamic range is fundamentally determined by the transduction system. In addition, a simple model derived from the nonlinearity of the plasma membrane could explain that a critical level of dynamic range was, at least in part, modified by the membrane nonlinearity. Address for reprint requests and other correspondence: A. Tomaru, c/o Professor Takashi Kurahashi, Dept. of Frontier Biosciences, Osaka Univ., Toyonaka, Osaka 560-8531, Japan (E-mail: kurahasi{at}bpe.es.osaka-u.ac.jp )