Studies of Conorfamide-Sr3 on Human Voltage-Gated Kv1 Potassium Channel Subtypes

Abstract

Recently, Conorfamide-Sr3 (CNF-Sr3) was isolated from the venom of Conus spurius and was demonstrated to have an inhibitory concentration-dependent effect on the Shaker K⁺ channel. The voltage-gated potassium channels play critical functions on cellular signaling, from the regeneration of action potentials in neurons to the regulation of insulin secretion in pancreatic cells, among others. In mammals, there are at least 40 genes encoding voltage-gated K⁺ channels and the process of expression of some of them may include alternative splicing. Given the enormous variety of these channels and the proven use of conotoxins as tools to distinguish different ligand- and voltage-gated ion channels, in this work, we explored the possible effect of CNF-Sr3 on four human voltage-gated K⁺ channel subtypes homologous to the Shaker channel. CNF-Sr3 showed a 10 times higher affinity for the Kv1.6 subtype with respect to Kv1.3 (IC₅₀ = 2.7 and 24 μM, respectively) and no significant effect on Kv1.4 and Kv1.5 at 10 µM. Thus, CNF-Sr3 might become a novel molecular probe to study diverse aspects of human Kv1.3 and Kv1.6 channels.

Keywords: CNF-Sr3; Conus spurius; FMRFamide peptides; Kv1 voltage-gated K+ channels; Shaker K+ channels; conorfamides.

Figure 1

Inhibition of human K_v1 channels by Conorfamide-Sr3 (CNF-Sr3). (A) K_v1.3, control current (◇); current in presence of CNF-Sr3 30 µM (◆). (B) K_v1.4, control current (◇); current in presence of CNF-Sr3 10 µM (◆). (C) K_v1.5, control current (◇); current in presence of CNF- Sr3 10 µM (◆). (D) K_v1.6, control current (◇); current in presence of CNF- Sr3 30 µM (◆). (E,F) Time course of inhibition by CNF-Sr3 on Kv1.3 and Kv1.6, respectively. CNF-Sr3 takes twice as much to block the current for Kv1.3 than Kv1.6. (G) CNF-Sr3 only inhibited Kv1.6 and Kv1.3 channels with low affinity: IC₅₀ of 2.7 ± 0.89 µM and 24 ± 4.06 µM, respectively (n=3 for each concentration; error bars = standard error of the mean (SEM).