Ca2(+)-dependent adaptive properties in the solitary olfactory receptor cell of the newt.

The time-dependent decay of the olfactory receptor potential was analyzed with a solitary cell preparation by using the whole-cell patch clamp technique. During prolonged stimulation by 10 mM N-amylacetate under standard conditions, 17 out of 63 isolated olfactory cells responded with slow depolarization. Of these 17 cells, response amplitudes in 14 cells ('phasic/tonic' response) gradually decayed within 9 s, with a half-decay time of 1.71 +/- 1.10 s (mean +/- S.D.). The relative amplitude (ratio of tonic component to peak amplitude, Vtonic/Vmax) was 0.29 +/- 0.10. The response decay was attributed to the inactivation of the odorant-activated conductance. The recovery after inactivation, which was determined with double pulse experiments, was dependent on the resting interval. The inactivation of the odorant-activated conductance was found to be observed only when the external medium contained Ca2+. In addition, it was found that the odorant-activated conductance was capable of permeating Ca2+ (PCa/PNa = 6.5), and a rise in the internal EGTA concentration (to 50 mM) inhibited the inactivation. These observations suggest that the decay of the olfactory response to prolonged stimulation is mediated by Ca2+ influx.