Potassium ion efflux induced by cationic compounds in yeast

New nanostructured extracellular potassium ion probe for assay of cellular K+ transport

The concentration of potassium ion is an important indicator for human health, and its abnormality is often accompanied by various diseases. However, most tools currently used to study potassium ion transport are low throughput. Herein, we reported a new K+ fluorescent nanoprobe CP1-KS with high selectivity and sensitivity to K+ (fluorescence enhanced factor was up to 9.91 at 20 mM K+). The polymeric fluorescent probe CP1-KS was composed of the small-molecular K+ indicator KS and amphiphilic copolymer CP1. This sensor can be easily and uniformly dispersed in cell culture medium and is suitable for high throughput analysis. To assess the utility of the probe CP1-KS in biological field, this probe was employed as an extracellular fluorescent probe to monitor the efflux of K+ from cells (E coli, B. Subtilis 168, Hela and MCF-7 cells) under various stimulation including lysozyme, nigericin, digitonin, and ATP. Results demonstrated that CP1-KS is an effective analysis tool for extracellular K+ concentration. We believe that the nanoprobe has great potential in antibacterial drug screening, K+ ionophore function, K+ channel activity, cell membrane permeability analysis or other K+ related field in the future.

Study of the mechanism of ε-poly-l-lysine as an antifungal on Candida albicans and Saccharomyces cerevisiae

The antimicrobial activity of ε-poly-l-lysine (EPL) has been documented, but its antifungal activity on yeast is not well defined and its mechanism of action has been vaguely explained. Our studies revealed that on both, Candida albicans and Saccharomyces cerevisiae, the minimum inhibitory concentration (MIC) and the minimum fungicidal concentration (MFC) were 250 μg·mL^-1; EPL produced a K⁺ and Ca²⁺ efflux, and at higher concentrations also an efflux of material absorbing at 260 nm, small peptides, and phosphate is produced, along with the inhibition of fermentation and extracellular acidification and respiration. Moreover, growth was inhibited, reactive oxygen species (ROS) production increased, and cell viability decreased. The polycation also produced plasma membrane potential hyperpolarization. The effects were dependent both on the cell quantity and polycation concentration, as well as the media used. The plasma membrane disruption was confirmed by TEM and PI staining.

Comparative Analysis of the Intermolt and Postmolt Hepatopancreas Transcriptomes Provides Insight into the Mechanisms of Procambarus clarkii Molting Process

In the present study, we used RNA-Seq to investigate the expression changes in the transcriptomes of two molting stages (postmolt (M) and intermolt (NM)) of the red swamp crayfish and identified differentially expressed genes. The transcriptomes of the two molting stages were de novo assembled into 139,100 unigenes with a mean length of 675.59 bp. The results were searched against the NCBI, NR, KEGG, Swissprot, and KOG databases, to annotate gene descriptions, associate them with gene ontology terms, and assign them to pathways. Furthermore, using the DESeq R package, differentially expressed genes were evaluated. The analysis revealed that 2347 genes were significantly (p > 0.05) differentially expressed in the two molting stages. Several genes and other factors involved in several molecular events critical for the molting process, such as energy requirements, hormonal regulation, immune response, and exoskeleton formation were identified and evaluated by correlation and KEGG analysis. The expression profiles of transcripts detected via RNA-Seq were validated by real-time PCR assay of eight genes. The information presented here provides a transient view of the hepatopancreas transcripts available in the postmolt and intermolt stage of crayfish, hormonal regulation, immune response, and skeletal-related activities during the postmolt stage and the intermolt stage.

First Reports of Effects of Insulin, Human-like Insulin Receptors and Adapter Proteins in Acanthamoeba castellanii

The insulin receptor (IR) and insulin-like growth factor 1 receptor (IGF1-R) play key roles in growth, regulation of nutrient metabolism and carbohydrate homeostasis. Insulin-like molecules in prokaryotes and other early life have been reported. However, an account of metabolic effects of insulin, transcriptomic evidence of expression of glucose transporting channels (GLUT) and homology modelling of IR and IGF1-R like proteins in unicellular life-forms have yet to be established. Acanthamoeba spp. has existed for about 2 billion years and is one of the earliest mitochondriate unicellular eukaryotic cells on Earth. Despite Acanthamoeba spp. being grown in a medium called peptone-yeast-glucose (PYG) for over 50 years, the mechanism and regulation of glucose uptake by IR or IGF1-R molecules in this microbe has not yet been reported. Several methods were utilized to validate the effects of insulin on trophozoites of A. castellanii, including: growth assays with insulin, estimation of glucose and potassium (K+) entry into the cell, and histology showing anabolic effects on proteins. Bioinformatic computational tools and homology modeling demonstrated the involvement of IR like proteins, GLUT, and adapter proteins in mediating the IR cascade. Growth assays showed proliferative effects in a dose range of 2.98-5.97 µmol/mL of insulin. After insulin exposure, A. castellanii trophozoites displayed enhanced Periodic acid-Sciff (PAS) staining. Amino acid sequence similarities and homology modelling revealed ACA1_163470 in Acanthamoeba spp. to be a homolog of human-IR. Acanthamoeba protein ACA1_336150 shares similarities with IGF1-R. Additionally, some proteins like ACA1_060920 have attributes of GLUT like channels on homology modelling and show similarity with human GLUT. Knowledge of IR and insulin effects in Acanthamoeba spp. contributes to its biology and advances current understanding behind the evolution of IR and IGF1-R signalling cascade.

Effects of chitosan on Candida albicans: conditions for its antifungal activity

The effects of low molecular weight (96.5 KDa) chitosan on the pathogenic yeast Candida albicans were studied. Low concentrations of chitosan, around 2.5 to 10 μg·mL⁻¹ produced (a) an efflux of K⁺ and stimulation of extracellular acidification, (b) an inhibition of Rb⁺ uptake, (c) an increased transmembrane potential difference of the cells, and (d) an increased uptake of Ca²⁺. It is proposed that these effects are due to a decrease of the negative surface charge of the cells resulting from a strong binding of the polymer to the cells. At higher concentrations, besides the efflux of K⁺, it produced (a) a large efflux of phosphates and material absorbing at 260 nm, (b) a decreased uptake of Ca²⁺, (c) an inhibition of fermentation and respiration, and (d) the inhibition of growth. The effects depend on the medium used and the amount of cells, but in YPD high concentrations close to 1 mg·mL⁻¹ are required to produce the disruption of the cell membrane, the efflux of protein, and the growth inhibition. Besides the findings at low chitosan concentrations, this work provides an insight of the conditions required for chitosan to act as a fungistatic or antifungal and proposes a method for the permeabilization of yeast cells.

Triazacryptand-based fluorescent sensors for extracellular and intracellular K+ sensing

A 4-amino-naphthalimide derived fluorophore with a triazacryptand moiety ligand was synthesized as a potassium ion (K(+)) sensor (KS1). This sensor is a monomer possessing a polymerizable vinyl group. By taking advantage of the polymerizable characteristics of the vinyl group, KS1 was polymerized with 2-hydroxyethyl methacrylate (HEMA) and acrylamide (AM) to form K(+) sensing films for extracellular sensing. The sensitivity of the films to potassium ions can be further tuned through the adjustment of the HEMA and AM weight ratios as well as introduction of positive or negative charge-containing segments. KS1 and its poly(2-hydroxyethyl methacrylate)-co-poly(acrylamide) (PHEMA-co-PAM) thin films show high selectivity for K(+) over competing sodium ions (Na(+)) at physiological concentrations. Extracellular sensing was demonstrated using a KS1-conjugated PHEMA-co-PAM thin film to measure the K(+) efflux of Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) stimulated by lysozyme. Meanwhile, KS1 itself permeates human glioblastoma U87MG and human esophagus premalignant CP-A cell lines. KS1 was used to monitor K(+) efflux stimulated by adenosine-5'-triphosphate (ATP), amphotericin, and a mixture of nigericin, bumetanide and ouabain, demonstrating application of this material as an intracellular potassium ion sensor.

Ketoconazole and miconazole alter potassium homeostasis in Saccharomyces cerevisiae

The effects of ketoconazole and miconazole uptake on K(+) transport and the internal pH of Saccharomyces cerevisiae were studied. The uptake of both drugs was very fast, linear with concentration and not dependent on glucose, indicating entrance by diffusion and concentrating inside. Low (5.0μM) to intermediate concentrations (40μM) of both drugs produced a glucose-dependent K(+) efflux; higher ones also produced a small influx of protons, probably through a K(+)/H(+) exchanger, resulting in a decrease of the internal pH of the cells and the efflux of material absorbing at 260nm and phosphate. The cell membrane was not permeabilized. The K(+) efflux with miconazole was dependent directly on the medium pH. This efflux results in an increased membrane potential, responsible for an increased Ca(2+) uptake and other effects. These effects were not observed with two triazolic antifungals. A decrease of the Zeta (ζ) potential was observed at low concentrations of miconazole. Although the main effect of these antifungals is the inhibition of ergosterol synthesis, K(+) efflux is an important additional effect to be considered in their therapeutic use. Under certain conditions, the use of single mutants of several transporters involved in the movements of K(+) allowed to identify the participation of several antiporters in the efflux of the cation.

Effects of amiodarone on K+, internal pH and Ca2+ homeostasis in Saccharomyces cerevisiae

In this study, amiodarone, at very low concentrations, produced a clear efflux of K(+). Increasing concentrations also produced an influx of protons, resulting in an increase of the external pH and a decrease of the internal pH. The K(+) efflux resulted in an increased plasma membrane potential difference, responsible for the entrance of Ca(2+) and H(+), the efflux of anions and the subsequent changes resulting from the increased cytoplasmic Ca(2+) concentration, as well as the decreased internal pH. The Deltatok1 and Deltanha1 mutations resulted in a smaller effect of amiodarone, and Deltatrk1 and Deltatrk2 showed a higher increase of the plasma membrane potential. Higher concentrations of amiodarone also produced full inhibition of respiration, insensitive to uncouplers and a partial inhibition of fermentation. This phenomenon appears to be common to a large series of cationic molecules that can produce the efflux of K(+), through the reduction of the negative surface charge of the cell membrane, and the concentration of this cation directly available to the monovalent cation carriers, and/or producing a disorganization of the membrane and altering the functioning of the carriers, probably not only in yeast.

Antimicrobial action of palmarosa oil (Cymbopogon martinii) on Saccharomyces cerevisiae

The essential oil extracted from palmarosa (Cymbopogon martinii) has proven anti-microbial properties against cells of Saccharomyces cerevisiae. Low concentrations of the oil (0.1%) inhibited the growth of S. cerevisiae cells completely. The composition of the sample of palmarosa oil was determined as 65% geraniol and 20% geranyl acetate as confirmed by GC-FTIR. The effect of palmarosa oil in causing K(+) leakage from yeast cells was attributed mainly to geraniol. Some leakage of magnesium ions was also observed. Blocking potassium membrane channels with caesium ions before addition of palmarosa oil did not change the extent of K(+) ion leakage, which was equal to the total sequestered K(+) in the cells. Palmarosa oil led to changes in the composition of the yeast cell membrane, with more saturated and less unsaturated fatty acids in the membrane after exposure of S. cerevisiae cells to the oil. Some of the palmarosa oil was lost by volatilization during incubation of the oil with the yeast cells. The actual concentration of the oil components affecting the yeast cells could not therefore be accurately determined.

Plasma membrane injury induced by nonyl gallate in Saccharomyces cerevisiae

AIMS

The aim was to investigate the antifungal actions of nonyl gallate against Saccharomyces cerevisiae ATCC 7754.

METHODS AND RESULTS

The maximum potency of both the growth inhibitory and the fungicidal effect against the yeast strain was found in nonyl gallate among n-alkyl gallates tested. Nonyl gallate induced ROS generation dose-dependently in growing cells. This ester rapidly killed yeast cells even when cell division was restricted by cycloheximide. This ester inhibited glucose-induced medium acidification and promoted the efflux of intracellular potassium ions in a nongrowing condition. Moreover, nonyl gallate induced a leakage of calcein from artificially prepared liposomes to a greater extent than dodecyl gallate did.

CONCLUSIONS

These results suggested nonyl gallate injured plasma membrane of S. cerevisiae, resulting in its exhibition of fungicidal effect accompanying with a leakage of intracellular materials from the cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our study reveals new knowledge on the antifungal actions of nonyl gallate against S. cerevisiae. When nonyl gallate is applied as a food preservative, the level of its addition to foods may be reduced because of its potent antifungal activity compared with weak acids including sorbic acid and benzoic acid.

Potassium release, a useful tool for studying antimicrobial peptides

We used an ion-selective electrode to measure potassium release from bacteria treated with antimicrobial peptides. This broadly applicable and simple technique for assessing membrane integrity deserves greater use.