Overview
Alomone Labs κ-Conotoxin-RIIIK inhibits KV1.2 channels heterologously expressed in Xenopus oocytes.A. Time course of κ-Conotoxin-RIIIK (#STC-650) action on KV1.2 currents. Current amplitudes were plotted as a function of time. Membrane potential was held at -80 mV and oocytes were stimulated by a 100 ms voltage ramp to +20 mV. 200 nM κ-Conotoxin-RIIIK was perfused as indicated by the bar at +10 mV. B. Superimposed examples of KV1.2 channel current in the absence (control) and presence of 200 nM κ-Conotoxin-RIIIK (taken from the experiment in A).
KV1.2 is a mammalian voltage-dependent K+ channel, homologous to the Drosophila Shaker K+ channel. KV1.2 was first cloned from rat brain1. Eight Shaker related genes exist in mammals constituting the KV1, subfamily of the large KV channel family of genes2.
The channel is expressed in neurons and cardiac and smooth muscle tissue as well as in retina and pancreas2. The crystal structure of KV1.2 was recently solved shedding light on the structure of a mammalian voltage-dependent channel3. The functional channel is considered low voltage activated and shows very little inactivation. Therefore, this channel activity influences the membrane potential and excitability of neurons and muscle.
KV1.2 channels are sensitive to high doses of TEA (560 mM) and low doses of 4-AP (0.59 mM), the “classical” non-selective potassium channel blockers.
Conotoxins, which are peptides consisting of 10 to 30 amino acid residues, typically have one or more disulfide bonds. Conotoxins have a variety of mechanisms of actions, most of which have not been determined. However, it appears that many of these peptides modulate the activity of ion channels4.
κ-Conotoxin RIIIK is a 24 amino acid peptidyl toxin isolated from the Conus radiatus (Rayed cone) venom. It blocks Shaker and TSha1 K+ channels. Additionally, it was found that κM-conotoxin RIIIK blocks voltage-activated K+ channels with a novel pharmacophore that does not comprise a dyad motif5.
