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Original Article

A Novel Amplification Step in Squid Olfactory Transduction

Jonathan P. Danaceau^a,b and Mary T. Lucero^b

^a Interdepartmental Program in Neuroscience, School of Medicine, Salt Lake City, Utah 84108
^b Department of Physiology University of Utah, School of Medicine, Salt Lake City, Utah 84108
Department of Physiology, University of Utah, 410 Chipeta Way, Room 155, Salt Lake City, UT 84108-1270.801-581-3476

mary.lucero{at}m.cc.utah.edu

Olfactory receptor neurons (ORNs) from the squid, Lolliguncula brevis, respond to the odors L-glutamate or dopamine with increases in internal Ca²⁺ concentrations ([Ca²⁺]_i). To directly asses the effects of increasing [Ca²⁺]_i in perforated-patched squid ORNs, we applied 10 mM caffeine to release Ca²⁺ 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 Ca²⁺-dependent nonselective cation current. The strict dependence on internal Ca²⁺ and external Na⁺ indicated that the inward current was due to an electrogenic Na⁺/Ca²⁺ exchanger. Block of the caffeine-induced current by an inhibitor of Na⁺/Ca²⁺ exchange (50–100 µM 2',4'-dichlorobenzamil) and reversibility of the exchanger current, further confirmed its presence. We tested whether Na⁺/Ca²⁺ 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⁺/Ca²⁺ exchange was responsible for 26% of the total current associated with glutamate-induced odor responses. Although Na⁺/Ca²⁺ 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.

Key Words: electrogenic • dichlorobenzamil • chemoreception • sodium–calcium exchange • cephalopod

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