Membrane Hyperpolarization Drives Cation Influx and Fungicidal Activity of Amiodarone

Abstract

Cationic amphipathic drugs, such as amiodarone, interact preferentially with lipid membranes to exert their biological effect. In the yeast Saccharomyces cerevisiae, toxic levels of amiodarone trigger a rapid influx of Ca 2؉ that can overwhelm cellular homeostasis and lead to cell death. To better understand the mechanistic basis of antifungal activity, we assessed the effect of the drug on membrane potential. We show that low concentrations of amiodarone (0.1-2 M) elicit an immediate, dose-dependent hyperpolarization of the membrane. At higher doses (>3 M), hyperpolarization is transient and is followed by depolarization, coincident with influx of Ca 2؉ and H ؉ and loss in cell viability. Proton and alkali metal cation transporters play reciprocal roles in membrane polarization, depending on the availability of glucose. Diminishment of membrane potential by glucose removal or addition of salts or in pma1, tok1⌬, ena1-4⌬, or nha1⌬ mutants protected against drug toxicity, suggesting that initial hyperpolarization was important in the mechanism of antifungal activity. Furthermore, we show that the link between membrane hyperpolarization and drug toxicity is pHdependent. We propose the existence of pH-and hyperpolarization-activated Ca 2؉ channels in yeast, similar to those described in plant root hair and pollen tubes that are critical for cell elongation and growth. Our findings illustrate how membrane-active compounds can be effective microbicidals and may pave the way to developing membrane-selective agents.

Effects of Acridine Derivatives on Ca2+ Uptake by Candida albicans

“…Quinacrine produced a remarkable increase of Ca 2+ uptake, but the absence of an effect of this compound on growth, brings some doubt about the proposal that the increased Ca 2+ is responsible for the death of yeast cells, as suggested by several authors [18][19][20][21][22][23][24][25][26]. It appears that in order to inhibit growth, other effects are involved.…”

“…These studies were continued by Muend and Rao [20], and later by Maresova et al [21], who found a plasma membrane hyperpolarization that drives Ca 2+ influx into S.…”

New applications of pHluorin—measuring intracellular pH of prototrophic yeasts and determining changes in the buffering capacity of strains with affected potassium homeostasis

“…Increased pH in of the pma1-105 mutant was really a surprising observation, not easy to explain, as its inability to grow at low pH was generally assumed to be due to an excessive cytosol acidification. However, the main trouble with this mutant might perhaps be the significantly decreased membrane potential (Maresova et al, 2009;Stevens and Nichols, 2007) and thus reduced proton-motive force necessary for nutrient uptake. When plasma membrane is depolarized, and Pma1 does not have sufficient capacity to extrude protons, the cell might try to increase the pH by transporting protons elsewhere (e.g.…”

Single-Cell Analysis: Visualizing Pharmaceutical and Metabolite Uptake in Cells with Label-Free 3D Mass Spectrometry Imaging

“…In a cardiac cell, the incorporation of amiodarone into the cell membrane perturbs the properties of the phospholipid bilayer structure and contributes to its antiarrhythmic abilities. 35 Table 1: For the individual cells defined in the ion image in Figure 1C, the percent area of coverage, average amiodarone counts per pixel summed across the depth scale and cell diameters were calculated. The average amiodarone count per pixel was calculated by dividing the backgroundsubtracted intensity of the peak at m/z 646.0 summed over the ROI by the total number of pixels in the selected ROI.…”