Calcium mediates the activation of the inhibitory current induced by odorants in toad olfactory receptor neurons.

In toad olfactory neurons, a putrid odorant mixture inducing inhibitory responses increases Ca2+-activated K+ conductance, developing a hyperpolarizing receptor potential. Removal of extracellular Ca2+ or exposure to nifedipine reversibly reduced the inhibitory response, suggesting that odorants induce a Ca2+ influx. We show evidence for an odorant-induced Ca2+ current. Using confocal microscopy, it is shown that odorants induce a nifedipine-sensitive elevation of Ca2+ in the apical end of the cell. These results suggest an inhibitory mechanism in which an apical Ca2+ influx causes an increase in internal Ca2+, opening Ca2+-activated K2+ channels that lead to membrane hyperpolarization.