1. Department of Integrated Biosciences, The University of Tokyo, Chiba 277-8562, Japan
2. Laboratory of Neurogenetics and Behavior, The Rockefeller University, New York, New York 10065, USA
3. Present address: Laboratory of Neurogenetics and Behavior, The Rockefeller University, New York, New York 10065, USA.

Correspondence to: Kazushige Touhara¹ Correspondence and requests for materials should be addressed to K.T. (Email: touhara@k.u-tokyo.ac.jp).

Abstract

In insects, each olfactory sensory neuron expresses between one and three ligand-binding members of the olfactory receptor (OR) gene family, along with the highly conserved and broadly expressed Or83b co-receptor^{1, 2, 3, 4, 5, 6, 7, 8, 9}. The functional insect OR consists of a heteromeric complex of unknown stoichiometry but comprising at least one variable odorant-binding subunit and one constant Or83b family subunit^{10, 11, 12, 13, 14, 15, 16}. Insect ORs lack homology to G-protein-coupled chemosensory receptors in vertebrates¹⁷ and possess a distinct seven-transmembrane topology with the amino terminus located intracellularly^{10, 18}. Here we provide evidence that heteromeric insect ORs comprise a new class of ligand-activated non-selective cation channels. Heterologous cells expressing silkmoth, fruitfly or mosquito heteromeric OR complexes showed extracellular Ca²⁺ influx and cation-non-selective ion conductance on stimulation with odorant. Odour-evoked OR currents are independent of known G-protein-coupled second messenger pathways. The fast response kinetics and OR-subunit-dependent K⁺ ion selectivity of the insect OR complex support the hypothesis that the complex between OR and Or83b itself confers channel activity. Direct evidence for odorant-gated channels was obtained by outside-out patch-clamp recording of Xenopus oocyte and HEK293T cell membranes expressing insect OR complexes. The ligand-gated ion channel formed by an insect OR complex seems to be the basis for a unique strategy that insects have acquired to respond to the olfactory environment.

1. Department of Integrated Biosciences, The University of Tokyo, Chiba 277-8562, Japan
2. Laboratory of Neurogenetics and Behavior, The Rockefeller University, New York, New York 10065, USA
3. Present address: Laboratory of Neurogenetics and Behavior, The Rockefeller University, New York, New York 10065, USA.

Correspondence to: Kazushige Touhara¹ Correspondence and requests for materials should be addressed to K.T. (Email: touhara@k.u-tokyo.ac.jp).

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