Direct suppression by odorants of ionotropic glutamate receptors in newt retinal neurons

Odorants are known to suppress voltage-gated channels not only in olfactory receptor cells but also in neurons of outside of the olfactory system. Here we found that odorants suppress glutamate-gated channels in newt retinal neurons using the Ca²⁺ imaging technique. Bath application of 100 μM glutamate rose [Ca²⁺]_i under application of the voltage-gated Ca²⁺ channel blocker. Thus, [Ca²⁺]₁ rises in the neurons were most likely attributable to Ca²⁺ influx via Ca²⁺-permeable glutamate-gated channels rather than voltage-gated Ca²⁺ channels. A similar increase of [Ca²⁺]_i was observed by application of 100 μM NMDA and 50 μM kainate, suggesting that both NMDA and AMPA/kainate receptors were expressed in newt retinal neurons. Application of odorants, 1 mM amyl acetate and acetophenone, reversibly reduced [Ca²⁺]_i increased by glutamate, NMDA and kainate. This suggests that odorants can suppress not only voltage-gated channels but also ligand-gated channels such as NMDA and AMPA/kainate receptors.