Probucol and the cholesterol synthesis inhibitors simvastatin and triparanol regulate I_ks channel function differently

Abstract

Channels responsible for slowly activating delayed-rectifier potassium current (I(Ks)) are composed of KCNQ1 and KCNE1 subunits, and these channels play a role in the repolarization of cardiac action potentials. Recently, we showed that the antihyperlipidemic drug probucol, which induces QT prolongation, decreases the I(Ks) after 24-h treatment. In the present study, we investigated the effects of three cholesterol-lowering agents (probucol, an enhancer of cholesterol efflux; simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor; and triparanol, a 3β-hydroxysterol-▵24-reductase inhibitor) on cholesterol synthesis, the KCNQ1 current (I KCNQ1), and the I(Ks) to clarify the differences in the modes of action of these agents on the I(Ks). Probucol did not inhibit cholesterol synthesis and had no effect on I KCNQ1, while I(Ks) decreased after 24-h treatment. Simvastatin inhibited cholesterol synthesis and decreased I KCNQ1 and I(Ks). Additionally, the activation kinetics of I(Ks) became faster, compared with that of control I(Ks). Triparanol inhibited cholesterol synthesis but did not reduce I KCNQ1 and I(Ks). However, the activation kinetics of I(Ks) became faster. Our data indicated that the mechanism by which probucol inhibits I(Ks) was not mediated by the inhibition of cholesterol synthesis but depended on an interaction with the KCNQ1/KCNE1 complex. Meanwhile, the reduction in cholesterol induced by simvastatin and triparanol is one of the mechanisms that affects the kinetics of I(ks).

A Long QT Mutation Substitutes Cholesterol for Phosphatidylinositol-4,5-Bisphosphate in KCNQ1 Channel Regulation

“…Since cyclodextrin is not very specific, we used another way of depleting membrane cholesterol. We selected triparanol because it has been shown to decrease cholesterol in a similar model [6]. In all these approaches we measured the relative tail-current amplitude of WT and mutant channels after a depolarization to +80 mV, during 1.1-mmol/L free Mg 2+ application in the giant-patch configuration.…”

“…For cholesterol depletion experiments, two different approaches were used: one-hour pre-treatment of 2 mmol/L 2-hydroxypropyl-β-cyclodextrin in Tyrode solution at 37°C or twenty-four hour pre-treatment of 10 µmol/L triparanol [6] in 1 ml of the cell culture medium. Free magnesium activities in gluconate-containing solutions were calculated using software designed by G. L. Smith (University of Glasgow, Scotland), using stability constants [29].…”

“…Similarly to Kir channels, functional effects of cholesterol on voltage-gated (Kv) channel activity are highly variable: an increase in Kv2.1 current in Drosophila neurons [3] and a suppression of the same current in mammalian pancreatic β-cells [4]. Adding more complexity, effects on the cardiac potassium channel KCNQ1 are variable depending on the drug used to decrease cholesterol levels [5], [6]. More specifically, Probucol - known as a cholesterol depleting agent - is able to decrease the coexpressed KCNE1/KCNQ1 current amplitude [5] without decreasing cholesterol levels in CHO-K1 [6].…”

“…Adding more complexity, effects on the cardiac potassium channel KCNQ1 are variable depending on the drug used to decrease cholesterol levels [5], [6]. More specifically, Probucol - known as a cholesterol depleting agent - is able to decrease the coexpressed KCNE1/KCNQ1 current amplitude [5] without decreasing cholesterol levels in CHO-K1 [6]. Simvastatin and triparanol are more specific since their main effects (activation kinetics) are similar and correlated to a cholesterol decrease.…”

Regulation of KCNQ/Kv7 family voltage-gated K + channels by lipids

“…Indeed in the case of KCNQ1, there is already evidence for additional modes of lipid regulation of function beyond those treated here, including modulation by sphingolipids [165], by cholesterol [150, 166, 167], and by association with lipid rafts [168, 169]. As is often the case in science, advances in technologies that help us understand and explain the world result in an expansion of the degree to which the situation is recognized to be almost unfathomably complex.…”