Identification of a cyclic nucleotide- and voltage-activated ion channel from insect antennae

Abstract

From an antennal cDNA library of Heliothis virescens a clone has been isolated encoding a polypeptide of 678 amino acids. Data base comparisons and primary structure analysis of the deduced protein sequence (HvCNG) indicated significant homology to cyclic nucleotide and voltage-activated ion channels including six putative membrane spanning domains, a putative cyclic nucleotide binding site, a pore region and a voltage-sensor motif. Heterologous expression of the cloned cDNA in Sf9 cells resulted in a polypeptide of the predicted molecular mass. Patch clamp analysis allowed to record the activity of the identified HvCNG channels; they were activated by cAMP but also by hyperpolarization. The channel displayed in potassium solution a conductance of 30 pS; the ion selectivity was calculated as P K/P Na ≈ 3. Northern blot analysis revealed that the channel is highly expressed in the antennae; weaker signal were detected in heads and legs. In situ hybridization of tissue sections through the antennae showed a spatial distribution of reactive cells; they are located beneath sensillar hairs. Thus, a novel channel type has been identified which may play an important role in antennal cells.