Mechanisms for Kir channel inhibition by quinacrine: acute pore block of Kir2.x channels and interference in PIP2 interaction with Kir2.x and Kir6.2 channels

Abstract

Cardiac inward rectifier potassium currents determine the resting membrane potential and contribute repolarization capacity during phase 3 repolarization. Quinacrine is a cationic amphiphilic drug. In this work, the effects of quinacrine were studied on cardiac Kir channels expressed in HEK 293 cells and on the inward rectifier potassium currents, I(K1) and I(KATP), in cardiac myocytes. We found that quinacrine differentially inhibited Kir channels, Kir6.2 ∼ Kir2.3 > Kir2.1. In addition, we found in cardiac myocytes that quinacrine inhibited I(KATP) > I(K1). We presented evidence that quinacrine displays a double action towards strong inward rectifier Kir2.x channels, i.e., direct pore block and interference in phosphatidylinositol 4,5-bisphosphate, PIP(2)-Kir channel interaction. Pore block is evident in Kir2.1 and 2.3 channels as rapid block; channel block involves residues E224 and E299 facing the cytoplasmic pore of Kir2.1. The interference of the drug with the interaction of Kir2.x and Kir6.2/SUR2A channels and PIP(2) is suggested from four sources of evidence: (1) Slow onset of current block when quinacrine is applied from either the inside or the outside of the channel. (2) Mutation of Kir2.3(I213L) and mutation of Kir6.2(C166S) increase their affinity for PIP(2) and lowers its sensitivity for quinacrine. (3) Mutations of Kir2.1(L222I and K182Q) which decreased its affinity for PIP(2) increased its sensitivity for quinacrine. (4) Co-application of quinacrine with PIP(2) lowers quinacrine-mediated current inhibition. In conclusion, our data demonstrate how an old drug provides insight into a dual a blocking mechanism of Kir carried inward rectifier channels.

Inward rectifier potassium (Kir) current in dopaminergic periglomerular neurons of the mouse olfactory bulb

“…Quinacrine is a molecule developed in the 1920s as anti-malarial agent, based upon the aminoacridine ring structure; more recently, it has been shown to inhibit different ionic currents, like the I A (Kehl, 1991), the L-type Ca 2+ current (Nagano et al, 1996) and the inward rectifier K + current (Evans and Surprenant, 1993; López-Izquierdo et al, 2011). We then tested quinacrine (100 μM), which suppresses a significant fraction of the hyperpolarization-activated current in DA-PG cells (Figure 7B): for voltage commands to -100 mV, the amplitude of the inward current was reduced from −17.16 ± 3.00 pA/pF (CTL) to −12.19 ± 2.98 pA/pF ( p < 0.001; n = 9; Two-Way ANOVA).…”

“…IRK2/KCNJ12; (Karschin et al, 1996); also KIR2.3 is weakly expressed in the glomerular layer (Inanobe et al, 2002; Allen Brain Atlas, 2013). Quinacrine, which differentially inhibits the K ir channels (KIR2.3 > KIR2.1 » KIR6.2; (López-Izquierdo et al, 2011), suppresses a large (46%) fraction of hyperpolarization-activated inward current. However, the presence of KIR6.x (a.k.a.…”

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

“…The Kir6.2 subunit has a low apparent affinity for PIP 2 relative to that of other Kir channels, and this property probably underlies a high sensitivity to inhibition by cationic amphiphilic drug (CADs) López-Izquierdo et al, 2011a). Kir6.2(C166S) increases the apparent PIP 2 affinity and renders molpharm.aspetjournals.org channels far less sensitive to rundown induced by PIP 2 depletion (Ribalet et al, 2006).…”

“…The order of reported channel sensitivity to CADs is Kir3.1/3.4 Ͼ Kir6.2 Ͼ Kir2.3 Ͼ Kir2.1 (Ponce-Balbuena et al, 2009López-Izquierdo et al, 2011a,b). Recently, we found that quinacrine induced a double action toward Kir channels, i.e., direct pore block of Kir2.1 and Kir2.3 and interference in PIP 2 -Kir channel interaction in a differential manner, Kir6.2 ϳ Kir2.3 Ͼ Kir2.1 (López-Izquierdo et al, 2011a).…”

“…First, chloroquine may block Kir6.2 channels via interaction with a binding site within the transmembrane vestibule. Second, chloroquine may act as a cationic amphiphilic drug and interfere with channel interactions with PIP 2 , similar to the mechanism of action of tamoxifen, quinacrine, and mefloquine on I K1 , I KATP , and I KACh (Ponce-Balbuena et al, 2009López-Izquierdo et al, 2010, 2011a. In this study, we have investigated these potential mechanisms of chloroquine action on Kir6.2/SUR2A.…”