Citrate enhances olfactory receptor responses and triggers oscillatory receptor activity in the channel catfish

Citrate, a normal constituent of cellular metabolism, in a binary mixture with an amino acid enhanced asynchronous olfactory receptor responses in the channel catfish, Ictalurus punctatus. In addition, high concentrations of either citrate (> or =3 mM) alone or an amino acid (> or =0.1 mM) in a binary mixture with citrate (> or =1 mM) triggered synchronized voltage oscillations of olfactory receptor neurons (ORNs) known as "peripheral waves" (PWs). Binary mixtures containing lower concentrations of an amino acid also triggered PW activity if the concentration of citrate in the mixture was increased. Both the enhancement of asynchronous activity and the generation of PW activity were the result of citrate chelating calcium, which lowers the surface potential of ORNs making them hyperexcitable. These effects of citrate are replicated by EGTA. Inactivation of the chelating ability of citrate and EGTA with 1 mM calcium chloride, barium chloride, or strontium chloride abolished both the enhancement of asynchronous olfactory responses and PW activity, while not affecting olfactory receptor responses to the amino acids alone.