The molecular basis of chloroquine block of the inward rectifier Kir2.1 channel

Abstract

Although chloroquine remains an important therapeutic agent for treatment of malaria in many parts of the world, its safety margin is very narrow. Chloroquine inhibits the cardiac inward rectifier K ؉ current IK1 and can induce lethal ventricular arrhythmias. In this study, we characterized the biophysical and molecular basis of chloroquine block of Kir2.1 channels that underlie cardiac I K1. The voltage-and K ؉ -dependence of chloroquine block implied that the binding site was located within the ion-conduction pathway. Site-directed mutagenesis revealed the location of the chloroquine-binding site within the cytoplasmic pore domain rather than within the transmembrane pore. Molecular modeling suggested that chloroquine blocks Kir2.1 channels by plugging the cytoplasmic conduction pathway, stabilized by negatively charged and aromatic amino acids within a central pocket. Unlike most ionchannel blockers, chloroquine does not bind within the transmembrane pore and thus can reach its binding site, even while polyamines remain deeper within the channel vestibule. These findings explain how a relatively low-affinity blocker like chloroquine can effectively block I K1 even in the presence of high-affinity endogenous blockers. Moreover, our findings provide the structural framework for the design of safer, alternative compounds that are devoid of Kir2.1-blocking properties.IK1 ͉ ion channel ͉ KCNJ2 ͉ malaria ͉ polyamines

KCNJ2 mutation in short QT syndrome 3 results in atrial fibrillation and ventricular proarrhythmia

“…However, to our knowledge, no specific blocker of Kir2.1 exists that may have therapeutic potential. Tamoxifen (14) and chloroquine (15,16) block Kir2.1 channels at low micromolar concentration but display prominent effects on other potassium, calcium, and sodium channels. Nevertheless, chloroquine has been shown to effectively terminate both atrial and ventricular fibrillation (16) and has been deemed to be more effective than flecainide as an antifibrillatory agent in a sheep model of stretch-induced atrial fibrillation (16,17).…”

Molecular Mechanisms of Chloroquine Inhibition of Heterologously Expressed Kir6.2/SUR2A Channels

“…Chloroquine has been found to inhibit the strong inward rectifier Kir2.1 channel in a voltage-dependent manner; i.e., it produces stronger inhibition of outward than inward current. An alanine scan of Kir2.1 pore lining residues identified amino acids Glu224, Phe254, Asp259, and Glu299, located in the cytoplasmic pore region, as critical regulators of sensitivity to chloroquine block (Rodríguez-Menchaca et al, 2008). In contrast, the D172N mutation in the M2 transmembrane domain, important for strong polyamine-mediated inward rectification of Kir2.1, did not affect the chloroquine pore-blocking effects (Rodrí-guez-Menchaca et al, 2008).…”

“…In cardiac myocytes, chloroquine inhibits I K1 , I KACh , and I KATP with a similar potency (Noujaim et al, 2010), but at negative membrane potentials the effect on I K1 is smaller than the effect on I KATP . Comparative molecular modeling and ligand docking of chloroquine in the intracellular domains of Kir2.1 suggested that chloroquine interacts with negatively charged amino acids facing the cytoplasmic pore of the channel (Rodríguez-Menchaca et al, 2008;Noujaim et al, 2010). In contrast, chloroquine was predicted to bind the Kir6.2 cytoplasmic pore in a configuration that seemed unlikely to impede potassium ion permeation (Noujaim et al, 2010).…”

“…In addition, chloroquine inhibits the native cardiac inward rectifier currents, I K1 , I KATP and I KACh (Benavides-Haro and Sá nchez-Chapula, 2000;Sá nchez-Chapula et al, 2001;Noujaim et al, 2011). Chloroquine inhibits I K1 by interacting with two rings of negatively charged amino acids, formed by Glu224, Phe254, Asp255, Asp259, and Glu299 in the cytoplasmic pore of Kir2.1 (Rodríguez-Menchaca et al, 2008). The mechanisms of channel inhibition of I KATP and I KACh by chloroquine are not known.…”

Evaluation of the efficacy of transdermal delivery of chloroquine on Plasmodium berghei-infected male Sprague-Dawley rats: effects on blood glucose and renal electrolyte handling

“…African children with severe Plasmodium falciparum malaria often present with metabolic complications which include impairment of glucose homeostasis, cardiovascular and kidney functions partly ascribed to P. falciparum infection and/or drugs used manage malaria [1] .…”