Inositol-trisphosphate-dependent calcium currents precede cation currents in insect olfactory receptor neurons in vitro.

Specialized olfactory receptor neurons in insects respond to species-specific sex pheromones with transient rises in inositol trisphosphate and by opening pheromone-dependent cation channels. These channels resemble cation channels which are directly or indirectly Ca(2+)-dependent. But there appear to be no internal Ca2+ stores in the outer dendrite where the olfactory transduction cascade is thought to start. Hence, it remains to be determined whether an influx of external Ca2+ precedes pheromone-dependent cation currents. Patch clamp measurements in cultured olfactory receptor neurons from Manduca sexta reveal that a transient inward current precedes pheromone-dependent cation currents. A transient inositol trisphosphate-dependent Ca2+ current, also preceding cation currents with the characteristics of pheromone-dependent cation currents, shares properties with the transient pheromone-dependent current. These results match the biochemical measurements with the electrophysiological data obtained in insect olfactory receptor neurons.