Electrogenic Na(+)/Ca(2+) exchange. A novel amplification step in squid olfactory transduction

Area of Science:

• Neuroscience
• Olfaction
• Cellular Physiology

Background:

• Olfactory receptor neurons (ORNs) in the squid Lolliguncula brevis detect odors like l-glutamate and dopamine.
• Odor detection in these neurons involves an increase in intracellular calcium concentrations ([Ca(2+)](i)).

Purpose of the Study:

• To investigate the role of intracellular calcium stores and ion exchangers in squid ORN odor transduction.
• To determine if Na+/Ca(2+) exchange contributes to the inward current generated by odor stimulation.

Main Methods:

• Perforated-patch recordings were used on squid ORNs.
• Caffeine was applied to release Ca(2+) from internal stores, inducing an inward current.
• Ion replacement (Na+) and specific inhibitors (2',4'-dichlorobenzamil) were used to identify the current's mechanism.
• The contribution of Na+/Ca(2+) exchange to l-glutamate-induced currents was assessed.

Main Results:

• Caffeine application induced an inward current in squid ORNs, dependent on internal Ca(2+) and external Na(+).
• This current was identified as an electrogenic Na(+)/Ca(2+) exchanger activity.
• The Na(+)/Ca(2+) exchanger inhibitor, 2',4'-dichlorobenzamil, blocked the caffeine-induced current.
• Electrogenic Na(+)/Ca(2+) exchange accounted for approximately 26% of the total current during l-glutamate stimulation.

Conclusions:

• The study provides the first evidence of Na(+)/Ca(2+) exchanger involvement in amplifying odor transduction in ORNs.
• Electrogenic Na(+)/Ca(2+) exchange significantly contributes to the signaling cascade initiated by odorants like l-glutamate.
• This finding highlights a conserved mechanism across species for enhancing olfactory signal detection.