Electrogenic Na(+)/Ca(2+) exchange. A novel amplification step in squid olfactory transduction.
Olfactory receptor neurons (ORNs) from the squid, Lolliguncula brevis, respond to the odors l-glutamate or dopamine with increases in internal Ca(2+) concentrations ([Ca(2+)](i)). To directly asses the effects of increasing [Ca(2+)](i) in perforated-patched squid ORNs, we applied 10 mM caffeine to release Ca(2+) from internal stores. We observed an inward current response to caffeine. Monovalent cation replacement of Na(+) from the external bath solution completely and selectively inhibited the caffeine-induced response, and ruled out the possibility of a Ca(2+)-dependent nonselective cation current. The strict dependence on internal Ca(2+) and external Na(+) indicated that the inward current was due to an electrogenic Na(+)/Ca(2+) exchanger. Block of the caffeine-induced current by an inhibitor of Na(+)/Ca(2+) exchange (50-100 microM 2',4'-dichlorobenzamil) and reversibility of the exchanger current, further confirmed its presence. We tested whether Na(+)/Ca(2+) exchange contributed to odor responses by applying the aquatic odor l-glutamate in the presence and absence of 2', 4'-dichlorobenzamil. We found that electrogenic Na(+)/Ca(2+) exchange was responsible for approximately 26% of the total current associated with glutamate-induced odor responses. Although Na(+)/Ca(2+) exchangers are known to be present in ORNs from numerous species, this is the first work to demonstrate amplifying contributions of the exchanger current to odor transduction.
Danaceau
J P
JP
Interdepartmental Program in Neuroscience, School of Medicine, Salt Lake City, UT 84108, USA.
Lucero
M T
MT
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000493:pharmacokinetics; D002478:Cells, Cultured; D002628:Chemoreceptor Cells / Q000737:chemistry / Q000378:metabolism; D049832:Decapodiformes; D018698:Glutamic Acid / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009761:Nystatin / Q000494:pharmacology; D009812:Odorants; D018034:Olfactory Receptor Neurons / Q000737:chemistry* / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011930:Reaction Time / Q000502:physiology; D012903:Smell / Q000502:physiology*; D012964:Sodium / Q000493:pharmacokinetics; D019831:Sodium-Calcium Exchanger / Q000378:metabolism*; D013268:Stimulation, Chemical
D007476:Ionophores; D010726:Phosphodiesterase Inhibitors; D019831:Sodium-Calcium Exchanger; C041470:3',4'-dichlorobenzamil; D009761:Nystatin; D002110:Caffeine; D018698:Glutamic Acid; D000584:Amiloride; D012964:Sodium; D002118:Calcium