PERSISTENCE OF THE OLFACTORY RECEPTOR CURRENT IN A WIDE VARIETY OF EXTRACELLULAR ENVIRONMENTS

1. We measured the current activated by cytoplasmic adenosine 3':5'-cy clic monophosphate (cAMP) in olfactory cilia from the frog Rana pipien s. The odorant-induced current in frog olfactory receptor neurons was also measured for comparison. In both cases, recordings were performed near the neuronal resting potential in a variety of extracellular bat h solutions. 2. In Ca2+-free baths, cAMP activated an inward current i n excised olfactory cilia that was carried entirely by cations. As ext racellular Ca2+ was increased, the cationic current decreased while a second current, carried by Cl-, increased. Total cAMP-activated curren t decreased with increasing extracellular Ca2+. When external Na+ but not Ca2+ was eliminated, only the Cl- component of the current persist ed. When external Na+ and Ca2+ were both removed, there was no cAMP-ac tivated current. 3. In receptor neurons, the total odorant-induced rec eptor current varied in a similar way with the extracellular ionic env ironment. Under conditions favoring the anionic receptor current, the response amplitude decreased and the latency increased. 4. It is known that olfactory receptor currents persist in a wide variety of extrace llular environments. This persistence can be sufficiently explained by the balance between cationic and anionic currents demonstrated here.