Interaction of anionic and cationic currents leads to a voltage dependence in the odor response of olfactory receptor neurons

Abstract

1. We recorded odor-induced currents from isolated olfactory receptor neurons of the land phase tiger salamander (Ambystoma tigrinum) with the whole cell patch clamp. 2. In a subset of cells the current-voltage relation for the odor-induced current showed a strong rectification with, in some cells, a negative resistance slope between about -45 and -25 mV. In these cells there was little or no odor-induced current at -55 mV, the average resting potential of olfactory neurons. 3. Depolarizing the membrane to +20 mV revealed a large outward current, and on repolarizing the membrane to -55 mV we could observe a large inward current. This current was not observed in the absence of the depolarizing step or in the absence of odor stimuli. 4. This odor-induced tail current was dependent on extracellular Ca2+ and voltage, activating with increased depolarization. The reversal potential was sensitive to the chloride equilibrium potential and it could be significantly blocked by niflumic acid, a blocker of calcium-activated chloride currents. The voltage dependence could result from either the voltage-dependent block of adenosine 3',5'-cyclic monophosphate-gated cation channels known to be activated by odorants and permeable to Ca2+, or from an inherent voltage dependence in the chloride channel gating. 5. The current appears to function as a regenerative mechanism that might increase the amplitude and duration of the odor-induced current, especially to low concentrations of stimulus.