Abstract
1. Ionic selectivity of the conductance activated by n-amyl acetate (odorant-activated conductance) was analysed in isolated olfactory receptor cells under the whole-cell voltage clamp condition. 2. Solitary receptor cells had a resting membrane potential of -44.7 +/- 7.0 mV (mean +/- S.D.; n = 70). Application of 10 mM-n-amyl acetate caused a depolarizing response in about 30% of the cells. Sensitivity to the odorant was maximum at around the apical dendrite. 3. Odorant induced an inward current to cells voltage clamped at their resting potential and bathed in the standard medium. The response amplitude was voltage dependent, and the polarity reversed at +2.5 +/- 2.2 mV (n = 6). The I-V relation was almost linear at membrane potentials more positive than -20 mV, with an average slope of 3.14 +/- 1.59 nS (measured at 0 mV), but showed a marked outward rectification at voltages more negative than -30 mV. 4. Removal of external Ca2+ increased the amplitude of the odorant-induced current and prolonged response duration, but did not cause a significant change on the reversal potential. Thus, Ca2+ affected the kinetics of the conductance, but did not seem to be a dominant charge carrier in the physiological condition. 5. Reduction of external Na+ concentration [( Na+]o) (replaced with choline) shifted the reversal potential by about 57 mV per 10-fold change of [Na+]o. Removal of external Cl- (replaced with glutamate ions) did not affect the reversal potential. 6. The odorant-activated conducting channels were permeable to all alkali metal ions. The permeability ratios were: PLi:PNa:PK:PRb:PCs = 1.25:1:0.98:0.84:0.80. 7. The present study strongly suggests that the olfactory receptor potential is generated by an increase in the membrane conductance to alkali metal ions.