The cyclic nucleotide-activated conductance in olfactory cilia: effects of cytoplasmic Mg2+ and Ca2+.

Olfactory receptor neurons depolarize in response to odorants. This depolarization is mediated by an increase in intracellular cyclic AMP, which directly gates channels in the membranes of the neuronal cilia. Previous evidence suggests that a Ca2+ influx during the odorant response may ultimately play a role in terminating the response. One way Ca2+ inside the cell could terminate the odorant response would be to directly inhibit the cAMP-gated channels. In this report the effects of cytoplasmic Ca2+ and Mg2+ on the cAMP-activated current were measured in single olfactory cilia. Near the neuronal resting potential, cytoplasmic Ca2+ and Mg2+ only slightly reduced the cAMP-activated current. Even at high levels (1.0 mM Ca2+ or 5.0 mM Mg2+), the average inhibition was only around 20%. It is therefore unlikely that an influx of divalent cations terminates the odorant response by a direct effect on the cAMP-gated channels.