Molecular cloning and functional characterization of a novel delayed rectifier potassium channel from channel catfish (Ictalurus punctatus): expression in taste buds

The gustatory system of channel catfish is widely studied for its sensitivi ty to amino acids. As a first step in identifying the molecular components that play a role in taste transduction in catfish, we cloned the full-lengt h cDNA for Kv2-catfish, a novel KC channel that is expressed in taste buds. The deduced amino acid sequence is 816 residues, and shares a 56-59% seque nce identity with Kv2.1 and Kv2.2, the other members of the vertebrate Kv2 subfamily of voltage-gated K+ channels. The Kv2-catfish RNA was expressed i n taste buds, brain, skeletal muscle, kidney, intestine and gills, and its gene is represented as a single copy in the catfish genome. Recombinant cha nnels expressed in Xenopus oocytes were selective for K+, and were inhibite d by tetraethylammonium applied to the extracellular side of the membrane d uring two-electrode voltage clamp analysis with a 50% inhibitory constant o f 6.1 mM. The channels showed voltage-dependent activation, and did not ina ctivate within 200 ms. Functionally, Kv2-catfish is a voltage-gated, delaye d rectifier KC channel, and its primary structure is the most divergent seq uence identified among the vertebrate members of the Kv2 subfamily of K+ ch annels, being related equally well to Kv2.1 and Kv2.2.