Intracellular Potassium Research Articles

A Highly Selective Mitochondria‐Targeting Fluorescent K+ Sensor

AbstractRegulation of intracellular potassium (K+) concentration plays a key role in metabolic processes. So far, only a few intracellular K+ sensors have been developed. The highly selective fluorescent K+ sensor KS6 for monitoring K+ ion dynamics in mitochondria was produced by coupling triphenylphosphonium, borondipyrromethene (BODIPY), and triazacryptand (TAC). KS6 shows a good response to K+ in the range 30–500 mM, a large dynamic range (Fmax/F0≈130), high brightness (ϕf=14.4 % at 150 mM of K+), and insensitivity to both pH in the range 5.5–9.0 and other metal ions under physiological conditions. Colocalization tests of KS6 with MitoTracker Green confirmed its predominant localization in the mitochondria of HeLa and U87MG cells. K+ efflux/influx in the mitochondria was observed upon stimulation with ionophores, nigericin, or ionomycin. KS6 is thus a highly selective semiquantitative K+ sensor suitable for the study of mitochondrial potassium flux in live cells.

Disinfection characteristics of the combined ultraviolet radiation and ozone process using Escherichia coli as a probe

In the present study, the characteristics of the combined ultraviolet (UV) and ozone disinfection process were investigated from kinetic and mechanistic viewpoints employing Escherichia coli (E. coli) as an indicator microorganism. Compared to individual unit processes, the combined UV/O3 tests produced excess hydroxyl radicals (HO•) and yielded synergistic inactivation of E. coli in the initial phase of reaction. The presence of O3 during UV exposure caused the destruction of cell structure, and then repressed bacteria regrowth after treatment. Moreover, the formation of malondialdehyde (MDA) showed that the improved generation of intermediate HO• via ozone photolysis accelerated the decomposition of bacterial cell surfaces, which was further confirmed by the leakage of intracellular potassium ions (K+). The results suggested that the synergistic bactericidal effect of combined UV/O3 owed mainly to the enhanced destruction of bacterial cell structure.

Farnesol activates the intrinsic pathway of apoptosis and the ATF4-ATF3-CHOP cascade of ER stress in human T lymphoblastic leukemia Molt4 cells

In this study, we demonstrate that treatment of T lymphoblastic leukemic Molt4 cells with farnesol activates the apoptosome via the intrinsic pathway of apoptosis. This induction was associated with changes in the level of intracellular potassium and calcium, the dissipation of the mitochondrial and plasma membrane potential, release of cytochrome c, activation of several caspases, and PARP cleavage. The induction of apoptosis by farnesol was inhibited by the addition of the pan-caspase inhibitor Z-VAD-fmk and by the exogenous expression of the anti-apoptotic protein Bcl2. Analysis of the gene expression profiles by microarray analysis revealed that farnesol increased the expression of several genes related to the unfolded protein response (UPR), including CHOP and CHAC1. This induction was associated with the activation of the PERK-eIF2α-ATF3/4 cascade, but not the XBP-1 branch of the UPR. Although farnesol induced activation of the ERK1/2, p38, and JNK pathways, inhibition of these MAPKs had little effect on farnesol-induced apoptosis or the induction of UPR-related genes. Our data indicate that the induction of apoptosis in leukemic cells by farnesol is mediated through a pathway that involves activation of the apoptosome via the intrinsic pathway and induction of the PERK-eIF2α-ATF3/4 cascade in a manner that is independent of the farnesol-induced activation of MAPKs.

Caspase-11 activates a canonical NLRP3 inflammasome by promoting K(+) efflux.

Recognition of microbe-associated molecular patterns or endogenous danger signals by a subset of cytosolic PRRs results in the assembly of multiprotein signaling complexes, the so-called inflammasomes. Canonical inflammasomes are assembled by NOD-like receptor (NLR) or PYHIN family members and activate caspase-1, which promotes the induction of pyroptosis and the release of mature interleukin-1β/-18. Recently, a noncanonical inflammasome pathway was discovered that results in caspase-11 activation in response to bacterial lipopolysaccharide (LPS) in the cytosol. Interestingly, caspase-11 induces pyroptosis by itself, but requires NLRP3, the inflammasome adapter ASC, and caspase-1 to promote cytokine secretion. Here, we have studied the mechanism by which caspase-11 controls IL-1β secretion. Investigating NLRP3/ASC complex formation, we find that caspase-11 functions upstream of a canonical NLRP3 inflammasome. The activation of NLRP3 by caspase-11 during LPS transfection is a cell-intrinsic process and is independent of the release of danger signals. Furthermore, we show that active caspase-11 leads to a drop of intracellular potassium levels, which is necessary to activate NLRP3. Our study, therefore, sheds new light on the mechanism of noncanonical inflammasome signaling.

The potassium transporter OsHAK21 functions in the maintenance of ion homeostasis and tolerance to salt stress in rice.

The intracellular potassium (K(+) ) homeostasis, which is crucial for plant survival in saline environments, is modulated by K(+) channels and transporters. Some members of the high-affinity K(+) transporter (HAK) family are believed to function in the regulation of plant salt tolerance, but the physiological mechanisms remain unclear. Here, we report a significant inducement of OsHAK21 expression by high-salinity treatment and provide genetic evidence of the involvement of OsHAK21 in rice salt tolerance. Disruption of OsHAK21 rendered plants sensitive to salt stress. Compared with the wild type, oshak21 accumulated less K(+) and considerably more Na(+) in both shoots and roots, and had a significantly lower K(+) net uptake rate but higher Na(+) uptake rate. Our analyses of subcellular localizations and expression patterns showed that OsHAK21 was localized in the plasma membrane and expressed in xylem parenchyma and individual endodermal cells (putative passage cells). Further functional characterizations of OsHAK21 in K(+) uptake-deficient yeast and Arabidopsis revealed that OsHAK21 possesses K(+) transporter activity. These results demonstrate that OsHAK21 may mediate K(+) absorption by the plasma membrane and play crucial roles in the maintenance of the Na(+) /K(+) homeostasis in rice under salt stress.

Regulated phosphorylation of the K-Cl cotransporter KCC3 is a molecular switch of intracellular potassium content and cell volume homeostasis.

The defense of cell volume against excessive shrinkage or swelling is a requirement for cell function and organismal survival. Cell swelling triggers a coordinated homeostatic response termed regulatory volume decrease (RVD), resulting in K+ and Cl− efflux via activation of K+ channels, volume-regulated anion channels (VRACs), and the K+-Cl− cotransporters, including KCC3. Here, we show genetic alanine (Ala) substitution at threonines (Thr) 991 and 1048 in the KCC3a isoform carboxyl-terminus, preventing inhibitory phosphorylation at these sites, not only significantly up-regulates KCC3a activity up to 25-fold in normally inhibitory isotonic conditions, but is also accompanied by reversal of activity of the related bumetanide-sensitive Na+-K+-2Cl− cotransporter isoform 1 (NKCC1). This results in a rapid (<10 min) and significant (>90%) reduction in intracellular K+ content (Ki) via both Cl-dependent (KCC3a + NKCC1) and Cl-independent [DCPIB (VRAC inhibitor)-sensitive] pathways, which collectively renders cells less prone to acute swelling in hypotonic osmotic stress. Together, these data demonstrate the phosphorylation state of Thr991/Thr1048 in KCC3a encodes a potent switch of transporter activity, Ki homeostasis, and cell volume regulation, and reveal novel observations into the functional interaction among ion transport molecules involved in RVD.

Zygosaccharomyces rouxii Trk1 is an efficient potassium transporter providing yeast cells with high lithium tolerance.

Zygosaccharomyces rouxii is an osmotolerant yeast growing in the presence of high concentrations of salts and/or sugars. The maintenance of intracellular potassium homeostasis is essential for osmostress adaptation. Zygosaccharomyces rouxii is endowed with only one typical potassium transporter (ZrTrk1). We characterized ZrTrk1 activity and its contribution to various physiological parameters in detail. Our results show that ZrTrk1 is a high-affinity K(+) transporting system efficiently discriminating between K(+) and Li(+) and indicate the presence of another, currently unknown K(+) importing system with a low affinity in Z. rouxii cells. Upon ZrTrk1 heterologous expression in Saccharomyces cerevisiae, it confers cells with a remarkably high lithium tolerance (even to wild-type strains) due to preventing Li(+) influx into cells, and is able to complement a plasma-membrane hyperpolarization and cell sensitivity to cationic compounds caused by the lack of endogenous K(+) transporters. Intracellular pH measurements with pHluorin, whose coding sequence was integrated into the genome, showed that the expression of ZrTrk1 also complements a decrease in intracellular pH in S. cerevisiae trk1Δ trk2Δ cells. Our data corroborate a tight connection between potassium and proton transporters in yeasts and provide new insights into Z. rouxii cation homeostasis and the basis of its high osmotolerance.

A jack of all trades: the multiple roles of the unique essential second messenger cyclic di-AMP.

Second messengers are key components of many signal transduction pathways. In addition to cyclic AMP, ppGpp and cyclic di-GMP, many bacteria use also cyclic di-AMP as a second messenger. This molecule is synthesized by distinct classes of diadenylate cyclases and degraded by phosphodiesterases. The control of the intracellular c-di-AMP pool is very important since both a lack of this molecule and its accumulation can inhibit growth of the bacteria. In many firmicutes, c-di-AMP is essential, making it the only known essential second messenger. Cyclic di-AMP is implicated in a variety of functions in the cell, including cell wall metabolism, potassium homeostasis, DNA repair and the control of gene expression. To understand the molecular mechanisms behind these functions, targets of c-di-AMP have been identified and characterized. Interestingly, c-di-AMP can bind both proteins and RNA molecules. Several proteins that interact with c-di-AMP are required to control the intracellular potassium concentration. In Bacillus subtilis, c-di-AMP also binds a riboswitch that controls the expression of a potassium transporter. Thus, c-di-AMP is the only known second messenger that controls a biological process by interacting with both a protein and the riboswitch that regulates its expression. Moreover, in Listeria monocytogenes c-di-AMP controls the activity of pyruvate carboxylase, an enzyme that is required to replenish the citric acid cycle. Here, we review the components of the c-di-AMP signaling system.

Neurologic Consequences of Electrolyte Disorders

Characteristically, several fluid and electrolyte disorders have dysfunction of the central nervous system (CNS) as a major complication. The brain, within a closed space, cannot respond quickly or effectively to prevent the acute stresses of osmotic swelling or contraction of extracellular and/or intracellular spaces. Disorders of many other ions and neutral molecules can lead to pathology, including cognitive abnormalities, encephalopathy, falls, and seizures. This chapter looks at osmolar change and brain volume regulation and the importance of sodium (Na), potassium, phosphate, and magnesium. The section on sodium looks at its importance to serum osmolality and discusses hyponatremia and hypernatremia, syndrome of inappropriate antidiuretic hormone (SIADH) and cerebral salt wasting, dialysis disequilibrium syndrome, and the CNS effects of elevated ammonia and altered glucose levels. The section on potassium discusses the ratio between the intracellular and extracellular potassium concentrations and looks at hypokalemia and hyperkalemia. Phosphate plays a vital role in energy metabolism, and this section explores hypercalcemia and hypocalcemia. Magnesium’s role in cell proliferation and energy metabolism is discussed, with subsections on hypomagnesemia and hypermagnesemia. Tables list symptoms of electrolyte disorders, ways to distinguish between SIADH and cerebral salt wasting, risk factors for osmotic demyelination, and expansion and contraction syndromes. Figures include a graph showing serum Na against urine osmolality in a patient with symptomatic hyponatremia, and a chart of a woman with hyperammonemia and severe metabolic acidosis. This chapter contains 2 highly rendered figures, 4 tables, 65 references, 5 MCQs.

Neurologic Consequences of Electrolyte Disorders

Characteristically, several fluid and electrolyte disorders have dysfunction of the central nervous system (CNS) as a major complication. The brain, within a closed space, cannot respond quickly or effectively to prevent the acute stresses of osmotic swelling or contraction of extracellular and/or intracellular spaces. Disorders of many other ions and neutral molecules can lead to pathology, including cognitive abnormalities, encephalopathy, falls, and seizures. This chapter looks at osmolar change and brain volume regulation and the importance of sodium (Na), potassium, phosphate, and magnesium. The section on sodium looks at its importance to serum osmolality and discusses hyponatremia and hypernatremia, syndrome of inappropriate antidiuretic hormone (SIADH) and cerebral salt wasting, dialysis disequilibrium syndrome, and the CNS effects of elevated ammonia and altered glucose levels. The section on potassium discusses the ratio between the intracellular and extracellular potassium concentrations and looks at hypokalemia and hyperkalemia. Phosphate plays a vital role in energy metabolism, and this section explores hypercalcemia and hypocalcemia. Magnesium’s role in cell proliferation and energy metabolism is discussed, with subsections on hypomagnesemia and hypermagnesemia. Tables list symptoms of electrolyte disorders, ways to distinguish between SIADH and cerebral salt wasting, risk factors for osmotic demyelination, and expansion and contraction syndromes. Figures include a graph showing serum Na against urine osmolality in a patient with symptomatic hyponatremia, and a chart of a woman with hyperammonemia and severe metabolic acidosis. This chapter contains 2 highly rendered figures, 4 tables, 65 references, 5 MCQs.

Role of mitochondrial fission and fusion in cardiomyocyte contractility

BackgroundMitochondria constitute 30% of cell volume and are engaged in two dynamic processes called fission and fusion, regulated by Drp-1 (dynamin related protein) and mitofusin 2 (Mfn2). Previously, we showed that Drp-1 inhibition attenuates cardiovascular dysfunction following pressure overload in aortic banding model and myocardial infarction. As dynamic organelles, mitochondria are capable of changing their morphology in response to stress. However, whether such changes can alter their function and in turn cellular function is unknown. Further, a direct role of fission and fusion in cardiomyocyte contractility has not yet been studied. In this study, we hypothesize that disrupted fission and fusion balance by increased Drp-1 and decreased Mfn2 expression in cardiomyocytes affects their contractility through alterations in the calcium and potassium concentrations. MethodsTo verify this, we used freshly isolated ventricular myocytes from wild type mouse and transfected them with either siRNA to Drp-1 or Mfn2. Myocyte contractility studies were performed by IonOptix using a myopacer. Intracellular calcium and potassium measurements were done using flow cytometry. Immunocytochemistry (ICC) was done to evaluate live cell mitochondria and its membrane potential. Protein expression was done by western blot and immunocytochemistry. ResultsWe found that silencing mitochondrial fission increased the myocyte contractility, while fusion inhibition decreased contractility with simultaneous changes in calcium and potassium. Also, we observed that increase in fission prompted decrease in Serca-2a and increase in cytochrome c leakage leading to mitophagy. ConclusionOur results suggested that regulating mitochondrial fission and fusion have direct effects on overall cardiomyocyte contractility and thus function.

Antimicrobial efficiency evaluation by monitoring potassium efflux for cellulose fibres functionalised by chitosan

As there is a large gap in the field of fibre microbiological testing, the successful establishment of appropriate techniques is extremely appreciated. Antimicrobials prevent bacterial cell division by damaging the cell wall or affecting the permeabilities of cells’ membranes; they denature proteins, block enzyme activity, prevent cell survival, etc. Intracellular potassium cations are released by the inhibitions of pathogenic micro-organisms. Their quantitative determination enables monitoring of the bactericidal effect regarding antimicrobials. It can be used as an alternative technique for determining the inhibition of micro-organisms in contact with antimicrobial agents. Chitosan, a biodegradable natural polymer, possesses antimicrobial characteristics that depend on a number of factors such as the protonated amino groups’ quantities, degree of acetylation, molecular weight, solvents, etc. Over recent years chitosan has become extremely attractive for fibre functionalization usage. The aim of this paper was to apply spectrophotometry and potentiometry using potassium ion-selective electrode, respectively, for the quantitative analysis of potassium efflux, resulting from the degradation of micro-organisms’ membranes in contact with chitosan itself, as well as with cellulose fibres functionalised by chitosan.

Cytotoxicity of cardiotonic steroids in sensitive and multidrug-resistant leukemia cells and the link with Na+/K+-ATPase

Cardiotonic steroids have long been in clinical use for treatment of heart failure and are now emerging as promising agents in various diseases, especially cancer. Their main target is Na+/K+-ATPase, a membrane protein involved in cellular ion homeostasis. Na+/K+-ATPase has been implicated in cancer biology by affecting several cellular events and signaling pathways in both sensitive and drug-resistant cancer cells. Hence, we investigated the cytotoxic activities of 66 cardiotonic steroids and cardiotonic steroid derivatives in sensitive CCRF-CEM and multidrug-resistant CEM/ADR5000 leukemia cells. Data were then subjected to quantitative structure-activity relationship analysis (QSAR) and molecular docking into Na+/K+-ATPase, which both indicated a possible differential expression of the pump in the mentioned cell lines. This finding was confirmed by western blotting, intracellular potassium labeling and next generation sequencing which showed that Na+/K+-ATPase was less expressed in multidrug-resistant than in sensitive cells.

A streptococcal lipid toxin induces membrane permeabilization and pyroptosis leading to fetal injury.

Group B streptococci (GBS) are Gram-positive bacteria that cause infections in utero and in newborns. We recently showed that the GBS pigment is hemolytic and increased pigment production promotes bacterial penetration of human placenta. However, mechanisms utilized by the hemolytic pigment to induce host cell lysis and the consequence on fetal injury are not known. Here, we show that the GBS pigment induces membrane permeability in artificial lipid bilayers and host cells. Membrane defects induced by the GBS pigment trigger K+ efflux leading to osmotic lysis of red blood cells or pyroptosis in human macrophages. Macrophages lacking the NLRP3 inflammasome recovered from pigment-induced cell damage. In a murine model of in utero infection, hyperpigmented GBS strains induced fetal injury in both an NLRP3 inflammasome-dependent and NLRP3 inflammasome-independent manner. These results demonstrate that the dual mechanism of action of the bacterial pigment/lipid toxin leading to hemolysis or pyroptosis exacerbates fetal injury and suggest that preventing both activities of the hemolytic lipid is likely critical to reduce GBS fetal injury and preterm birth.

Biochemical storage lesions occurring in nonirradiated and irradiated red blood cells: a brief review.

Red blood cells undergo a series of biochemical fluctuations during 35–42-day storage period at 1°C to 6°C. The sodium/potassium pump is immobilised causing a decrease in intracellular potassium with an increase in cytoplasmic sodium levels, glucose levels decline, and acidosis occurs as a result of low pH levels. The frailty of stored erythrocytes triggers the formation of haemoglobin-containing microparticles and the release of cell-free haemoglobin which may add to transfusion difficulties. Lipid peroxidation, oxidative stress to band 3 structures, and other morphological and structural molecular changes also occur leading to spheroechinocytes and osmotic fragility. These changes that transpire in the red cells during the storage period are referred to as “storage lesions.” It is well documented that gamma irradiation exacerbates storage lesions and the reports of increased potassium levels leading to adverse reactions observed in neonates and infants have been of particular concern. There are, however, remarkably few systematic studies comparing the in vitro storage lesions of irradiated and nonirradiated red cell concentrates and it has been suggested that the impact of storage lesions on leucocyte reduced red blood cell concentrate (RBCC) is incomplete. The review examines storage lesions in red blood cells and their adverse effects in reference to blood transfusion.

Matrine Inhibits Mouse Sperm Function by Reducing Sperm [Ca2+]i and Phospho-ERK1/2

Background: Matrine is a bioactive alkaloid that has a variety of pharmacological effects and is widely used in Chinese medicine. However, its effects on male reproduction are not well known. In this study, we aimed to investigate the in vitro toxicity of matrine on mature mouse sperm. Methods: Mouse cauda epididymal sperm were exposed to matrine (10-200 µM) in vitro. The viability, motility, capacitation, acrosome reaction and fertilization ability of the mouse sperm were examined. Furthermore, the intracellular calcium concentration ([Ca²⁺]_i), calcium (Catsper) and potassium (Ksper) currents, and phosphorylation of extracellular signal regulated kinases 1/2 (p-ERK1/2) of the sperm were analyzed. Results: After exposure to 100 µM or more of matrine, mouse cauda epididymal sperm exhibited a significant reduction in total motility, progressive motility, linear velocity and acrosome reaction rate induced by Ca²⁺ ionophore A23187. As a result, the fertilization ability of mouse sperm was remarkably decreased by matrine. Our data further demonstrated that matrine significantly reduced sperm [Ca²⁺]_i and [Ca²⁺]_i-related p-ERK1/2; however, both the CatSper and KSper currents, which are thought to interactively regulate Ca²⁺ influx in sperm, were not affected by matrine. Conclusion: Our findings indicate that matrine inhibits mouse sperm function by reducing sperm [Ca²⁺]_i and suppressing the phosphorylation of ERK1/2.

Rhabdomyolysis in lumbar spinal surgery: Early detection is crucial.

Sir, Rhabdomyolysis (RM) after neurosurgical procedure is a rare event. We report a case of RM following lumbar surgery and discuss the importance of early recognition. A 22-year-old male underwent resection of L3 giant cell tumor in right lateral position. The patient weighed 96 kg with a body mass index (BMI) of 35.6 kg/m2 with no comorbidities. General anesthesia was administered with oxygen, nitrous oxide, isoflurane, propofol, and morphine. Surgery lasted for 9 h. On 1st postoperative day, he developed severe pain with a progressive increase in girth of the right thigh. Doppler study ruled out deep venous thrombosis. Next day, he developed tachycardia, tachypnea, and icterus. Concurrently, he had oliguria. Investigations showed a high serum creatinine (1.63 mg/dl), creatine phosphokinase (CPK) (29,100 U/L) and deranged liver function (total bilirubin 1.5 mg%, direct 0.5 mg%, aspartate aminotransferase 209 U/L, alanine aminotransferase 185 U/L, alkaline phosphate 372 U/L). A diagnosis of RM was made, and the patient was treated with liberal hydration to maintain urine output of at least 100 ml/h along with alkalinization of urine. Clinically and serologically, he started to improve and was ambulated and discharged in a week. There are only a few reported cases of RM after neurosurgical procedures, with several risk factors being proposed. Lateral positioning in posterior fossa tumor resection and minimally invasive spinal surgeries have been reported as probable cause in 9 patients.[1] Van Gompel et al. reviewed 10 cases of RM after neurosurgery in supine or prone positions for cranial and spinal pathologies, and found obesity and prolonged surgery as common risk factors.[2] Woernle et al. studied 150 patients with routine CPK analysis before and after surgery to determine the effect of position. They correlated raised CPK not only with lateral position, but also with the use of intraoperative monitoring, and hypothesized it to be due to the absence of pharmacological relaxation during monitoring.[3] In our case, several of these factors contributed to the development of RM. The patient was obese (BMI of 35.8 kg/m2), had a long surgery (9 h) in right lateral position. Use of isoflurane is thought to stress an unstable sarcolemmal membrane causing increased permeability resulting in an influx of calcium and leak of intracellular potassium and creatinine kinase from myocytes.[4] Acute renal failure (ARF) is the most dangerous complication of RM, with prompt recognition and early therapy determining the outcome. Adequate rehydration to maintain hourly urine output of 100–300 ml is the main component of management to prevent ARF, with alkalization of urine to maintain pH >7.5. The kidney disease improving global outcomes recommends against the use of diuretics to maintain an adequate output (level 1 B).[5] Hemodialysis is required if the kidneys do not respond. Rhabdomyolysis is a rare but potentially life-threatening postoperative complication in neurosurgery, with obesity, lateral position, and prolonged surgery being common risk factors. A high index of suspicion and early recognition helps prevent renal shutdown.

Epithelial sodium transport and its control by aldosterone: the story of our internal environment revisited.

Transcription and translation require a high concentration of potassium across the entire tree of life. The conservation of a high intracellular potassium was an absolute requirement for the evolution of life on Earth. This was achieved by the interplay of P- and V-ATPases that can set up electrochemical gradients across the cell membrane, an energetically costly process requiring the synthesis of ATP by F-ATPases. In animals, the control of an extracellular compartment was achieved by the emergence of multicellular organisms able to produce tight epithelial barriers creating a stable extracellular milieu. Finally, the adaptation to a terrestrian environment was achieved by the evolution of distinct regulatory pathways allowing salt and water conservation. In this review we emphasize the critical and dual role of Na(+)-K(+)-ATPase in the control of the ionic composition of the extracellular fluid and the renin-angiotensin-aldosterone system (RAAS) in salt and water conservation in vertebrates. The action of aldosterone on transepithelial sodium transport by activation of the epithelial sodium channel (ENaC) at the apical membrane and that of Na(+)-K(+)-ATPase at the basolateral membrane may have evolved in lungfish before the emergence of tetrapods. Finally, we discuss the implication of RAAS in the origin of the present pandemia of hypertension and its associated cardiovascular diseases.

The wheat NHX antiporter gene TaNHX2 confers salt tolerance in transgenic alfalfa by increasing the retention capacity of intracellular potassium.

Previous studies have shown that TaNHX2 transgenic alfalfa (Medicago sativa L.) accumulated more K(+) and less Na(+) in leaves than did the wild-type plants. To investigate whether the increased K(+) accumulation in transgenic plants is attributed to TaNHX2 gene expression and whether the compartmentalization of Na(+) into vacuoles or the intracellular compartmentalization of potassium is the critical mechanism for TaNHX2-dependent salt tolerance in transgenic alfalfa, aerated hydroponic culture was performed under three different stress conditions: control condition (0.1mM Na(+) and 6mMK(+) inside culture solution), K(+)-sufficient salt stress (100mMNaCl and 6mMK(+)) and K(+)-insufficient salt stress (100mM NaCl and 0.1mMK(+)). The transgenic alfalfa plants had lower K(+) efflux through specific K(+) channels and higher K(+) absorption through high-affinity K(+) transporters than did the wild-type plants. Therefore, the transgenic plants had greater K(+) contents and [K(+)]/[Na(+)] ratios in leaf tissue and cell sap. The intracellular compartmentalization of potassium is critical for TaNHX2-induced salt tolerance in transgenic alfalfa.

Stem bark extract and fraction of Persea americana (Mill.) exhibits bactericidal activities against strains of bacillus cereus associated with food poisoning.

The study investigates the in vitro antibacterial potentials of stem bark extracts of Persea americana on strains of Bacillus cereus implicated in food poisoning. The crude stem bark extracts and butanolic fraction at a concentration of 25 mg/mL and 10 mg/mL, respectively, exhibited antibacterial activities against test isolates. The zones of inhibition exhibited by the crude extract and the fraction ranged between 10 mm and 26 mm, while the minimum inhibitory concentration values ranged between 0.78 and 5.00 mg/mL. The minimum bactericidal concentrations ranged between 3.12 mg/mL–12.5 mg/mL and 1.25–10 mg/mL for the extract and the fraction, respectively. The butanolic fraction killed 91.49% of the test isolates at a concentration of 2× MIC after 60 min of contact time, while a 100% killing was achieved after the test bacterial cells were exposed to the butanolic fraction at a concentration of 3× MIC after 90 min contact time. Intracellular protein and potassium ion leaked out of the test bacterial cells when exposed to certain concentrations of the fraction; this is an indication of bacterial cell wall disruptions by the extract’s butanolic fraction and, thus, caused a biocidal effect on the cells, as evident in the killing rate test results.