• BMB Reports
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• v.38 no.4
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• pp.468-473
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• 2005

The energetics of nitrate uptake by intact cells of the halotolerant cyanobacterium Aphanothece halophytica were investigated. Nitrate uptake was inhibited by various protonophores suggesting the coupling of nitrate uptake to the proton motive force. An artificially-generated pH gradient across the membrane (${\Delta}pH$) caused an increase of nitrate uptake. In contrast, the suppression of ${\Delta}pH$ resulted in a decrease of nitrate uptake. The increase of external pH also resulted in an enhancement of nitrate uptake. The generation of the electrical potential across the membrane ($\Delta\psi$) resulted in no elevation of the rate of nitrate uptake. On the other hand, the valinomycin-mediated dissipation of $\Delta\psi$ caused no depression of the rate of nitrate uptake. Thus, it is unlikely that $\Delta\psi$ participated in the energization of the uptake of nitrate. However, $Na^+$-gradient across the membrane was suggested to play a role in nitrate uptake since monensin which collapses $Na^+$-gradient strongly inhibited nitrate uptake. Exogenously added glucose and lactate stimulated nitrate uptake in the starved cells. N, N'-dicyclohexylcarbodiimide, an inhibitor of ATPase, could also inhibit nitrate uptake suggesting that ATP hydrolysis was required for nitrate uptake. All these results indicate that nitrate uptake in A. halophytica is ATP-dependent, driven by ${\Delta}pH$ and $Na^+$-gradient.

• Bulletin of the Korean Chemical Society
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• v.24 no.1
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• pp.37-44
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• 2003

We examined the effect of polyether-type nonionic surfactants (Brij 35, Triton X-100, Tween 20 and Tween 80) on the potentiometric properties of sodium-, potassium- and calcium-selective membranes which are prepared with widely used ionophores and four kinds of polymer matrices [poly(vinyl chloride) (PVC), polyurethane (PU), PVC/PU blend, and silicone rubber (SR)]. It was found that the PVC-based membranes, which provide the best performance among all other matrix-based membranes in the absence of nonionic surfactants, exhibited larger change in their potentiometric properties when nonionic surfactants are added to the sample solution. On the other hand, the sodium-selective SR-based membrane with calix[4]arene, potassium-selective PVC/PU- or SR-based membrane with valinomycin, and the calcium-selective SR-based membrane with ETH 1001 provide almost identical analytical performance in the presence and absence of Tween 20 or Tween 80 surfactants. The origin of nonionic surfactants effect was also investigated by interpreting the experimental results obtained with various matrices and ionophores. The results suggest that the nonionic surfactant extracted into the membrane phase unselectively form complexes with the primary and interfering ions, resulting in increased background potential and lower binding ability for the ionophore. Such effects should result in deteriorated detection limits, reduced response slopes and lower selectivity for the primary ions.

• Journal of Environmental Health Sciences
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• v.26 no.4
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• pp.88-96
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• 2000

The aim of the current study was to evaluate the transport system in EMT-6 cell for the uptake of the methylmercury(MeHg). Several inhibitors ere used to test used to test which potential transport system might be involoved in MeHg uptake. Probenecid was used to test the organic transport system, valinomycin for testing the effect of the membrane potential, cytochalasin B for testing the facilitated diffusive D-glucose transport system and colchicine for testing the microtubule system. Ouabain for evaluating active transport system, 4',4-diisothiocyano-2',2-stilbenedisulfonic acid(DIDS) the Cl- ion transport system and verapamil for the $Ca^{2+}$ transprot system. Significantly, MeHg decreased the synthesis of nitric oxcide(NO) and intracellular ATP in ENT-6 cells. In the condition of ouabain containing with MeHg decreased the production of NO and intracelluar ATP. In the treatment of inhibitors, ouabain showed protective effect against cytotoxicity of MeHg but ather inhibitors not showed protective effects. The protective effects of ouabain against the cytotoxicity of MeHg deoended on the concentration of added ouabain to the culture medium for MET-6 cells. These result showed that the uptake of MeHg might be involved in the active transport system. Active transports system seems to share similarities with the transport systems for the uptake of MeHg when using MeHg and MeHg-glutathione complex.x.

• Journal of the Korean institute of surface engineering
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• v.55 no.3
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• pp.156-163
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• 2022

An ammonium ion with a size and charge similar to that of potassium can bind to valinomycin, which is used as an ion carrier for potassium, and cause a meaningful interference effect on the detection of potassium ions. Currently, there are few ion sensors that correct the interference effect of ammonium ions, and there are few studies that specifically suggest the mechanism of the interference effect. By fabricating a SPCE-based potassium ion-selective electrode, the electromotive force was measured in the concentration range of potassium in the nutrient solution, and the linear range was measured to be 10^-5 to 10^-2 M, and the detection limit was 10^-5.19 M. And the interference phenomenon of the potassium sensor was investigated in the concentration range of ammonium ions present in the nutrient solution. Therefore, a data-based analysis strategy using deep learning was presented as a method to minimize the interference effect.

• Microbiology and Biotechnology Letters
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• v.19 no.2
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• pp.128-134
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• 1991

To study the reduced growth and synthesis, proeviously reported, of ${\beta}$-galactosidase of alkalophilic Bacillus sp. YS-309 at the higher lactose concentration of 0.5% (w/v) in the medium, lactose transport and utilization were examined. The results showed that lactose transport was influenced by the addition of four kinds of antibiotics, and tetracycline stimulated most but not valinomycin. PEP-potentials of the cells grown on lactose was estimated lower than the cells on glucose and on galactose. Thus, the transport of lactose was independent of intracellular PEP and phosphorylation reactions, and was thought to be uptaked directly or oxidized in part in the transport process. In the other hand, once lactose was uptaked into the cells, it was hydrolyzed by ${\beta}$-glactosidase to glucose and galactose. The former was metabolized fast but the latter was accumulated. Galactose and lactose were not utilized until glucose was mostly depleted in the medium. The ${\beta}$-galactosidase synthesis decreased in the presence of glucose over 0.2% and galactose over 0.05 to 0.1%, respectively. In conclusion, it was considered for glucose as a repressor and galactose as a inducer for ${\beta}$-galactosidase synthesis even though the mechanisms were not elucidated. Catabolite repression of glucose on the enzyme synthesis was not relieved by the addition of exogeneous cAMP.

• Journal of Microbiology and Biotechnology
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• v.14 no.3
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• pp.456-465
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• 2004

$K^+$ efflux through a certain type of $K^+$ channels causes the change of membrane potential and leads to cAMP synthesis in the transmembrane cell signaling for the initiation of sperm motility in the salmonid fishes. The addition of $Ca^{2+}$ conferred motility to the trout sperm that were immobilized by external $K^+$ and other alkaline metals, $Rb^+$ and $Cs^{2+}$, suggesting the participation of external $Ca^{2+}$ in the initiation of sperm motility. L-type $Ca^{2+}$ channel blockers such as nifedipine, nimodipine, and FS-2 inhibited the motility, but N-type $Ca^{2+}$ channel blocker, w-conotoxin MvIIA, did not. On the other hand, the membrane hyperpolarization and cAMP synthesis were suppressed by $Ca^{2+}$ channel blockers, nifedipine, and trifluoroperazine. Furthermore, these suppressions were relieved by the addition of $K^+$ ionophore, valinomycin. Inhibitors of calmodulin, such as W-7, trifluoperazine, and calrnidazol-C1, inhibited the sperm motility, membrane hyperpolarization, and cAMP synthesis. The results suggest that $Ca^{2+}$ influx through $Ca^{2+}$ channels that are sensitive to specific $Ca^{2+}$ channel blockers and calmodulin participate in the changes of membrane potential, leading to synthesis of cAMP in the cell signaling for the initiation of trout sperm motility.

• The Korean Journal of Physiology and Pharmacology
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• v.9 no.1
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• pp.37-43
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• 2005

Our previous report demonstrated that chick myoblasts are equipped with $Ca^{2+}$-permeable stretchactivated channels and $Ca^{2+}-activated$ potassium channels ($K_{Ca}$), and that hyperpolarization-induced by $K_{Ca}$ channels provides driving force for $Ca^{2+}$ influx through the stretch-activated channels into the cells. Here, we showed that acetylcholine (ACh) also hyperpolarized the membrane of cultured chick myoblasts, suggesting that nicotinic acetylcholine receptor (nAChR) may be another pathway for $Ca^{2+}$ influx. Under cell-attatched patch configuration, ACh increased the open probability of $K_{Ca}$ channels from 0.007 to 0.055 only when extracellular $Ca^{2+}$ was present. Nicotine, a nAChR agonist, increased the open probability of $K_{Ca}$ channels from 0.008 to 0.023, whereas muscarine failed to do so. Since the activity of $K_{Ca}$ channel is sensitive to intracellular $Ca^{2+}$ level, nAChR seems to be capable of inducing $Ca^{2+}$ influx. Using the $Ca^{2+}$ imaging analysis, we were able to provide direct evidence that ACh induced $Ca^{2+}$ influx from extracellular solution, which was dramatically increased by valinomycin-mediated hyperpolarization. In addition, ACh hyperpolarized the membrane potential from $-12.5{\pm}3$ to $-31.2{\pm}5$ mV by generating the outward current through $K_{Ca}$ channels. These results suggest that activation of nAChR increases $Ca^{2+}$ influx, which activates $K_{Ca}$ channels, thereby hyperpolarizing the membrane potential in chick myoblasts.

• The Korean Journal of Physiology
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• v.25 no.1
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• pp.49-60
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• 1991

The change of the acridine orange absorbance was used to monitor the formation and/or dissipation of a pH gradient in microvillous membrane vesicles (MVV) isolated from human term placenta. Under $Na^+$ efflux conditions, an acidification of the intravesicular space occured and it was completely inhibited by 0.1 mM amiloride. Under $K^+$ efflux conditions, an acidification of the intravesicular space occured and it was potentiated by valinomycin or FCCP. An inwardly directed chloride gradient also induced a minor intravesicular acidification, but it was not observed in voltage-clampled MVV. The initial rate of the dissipation of a pH gradient was accelerated by pulse injections of $Na^+$ in a saturable manner and $Li^+$ could replace $Na^+$. The kinetic parameter of $Na^+$ in placental $Na^+/H^+$ exchange was similar to that of renal $Na^+/H^+$ exchange. Amiloride was a inhibitor of directly coupled $Na^+/H^+$ exchange and its $IC_{50}$ in placental MVV was about 14-fold higher than that in renal brush border membrane. These results indicate that $Na^+/H^+$ exchanger exists in human placental MVV and that its kinetic characteristics is similar to that of renal $Na^+/H^+$ exchanger but its pharmacological characteristics is different. In placental MVV $K^+,\;H^+$, and, relatively minor chloride conductances are present. The magnitude of $Cl^-/OH^-$ exchange, even though it exists, seems to be smaller than that of $Na^+/H^+$ exchange.

• The Korean Journal of Physiology
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• v.23 no.2
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• pp.237-252
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• 1989

Effect of a $Na^+$ gradient on $Ca^{2+}$ uptake was studied in isolated sarcolemmal vesicles of cat ileal longitudinal muscle. $Ca^{2+}$ uptake was markedly stimulated in the presence of an outwardly directed $Na^+$ gradient. External $Na^+$, monensin and A23187 abolished the $Na^+-dependent$ $Ca^{2+}$ uptake. Monovalent cations such as $K^+$, $Li^+$, $Rb^+$, $Cs^+$ and choline could not substitute for $Na^+$ in enhancement of $Ca^{2+}$ uptake. Divalent cations such as $Ba^{2+}$, $Sr^{2+}$, $Mn^{2+}$ and $Cd^{2+}$ but not $Mg^{2+}$ inhibited the $Na^+-dependent$ $Ca^{2+}$ uptake. Increase in external pH in the range of 6.0 to 8.0 stimulated the $Na^+-dependent$ $Ca^{2+}$ uptake. Amiloride inhibited the $Na^+-dependent$ $Ca^{2+}$ uptake at concentrations above 0.5 mM, whereas diltiazem or vanadate did not. The apparent Km of the $Na^+-dependent$ $Ca^{2+}$ uptake for $Ca^{2+}$ was 18.2 ${\mu}M$ and apparent Vmax was 689.7 pmole/mg protein/5 sec. Kinetic analysis of the $Na^+-dependent$ $Ca^{2+}$ uptake showed a noncompetitive interaction between internal $Na^+$ and external $Ca^{2+}$. The dependence of $Ca^{2+}$ uptake on internal $Na^+$ showed sigmoidal kinetics and Hill coefficient for internal $Na^+$ was 2.52. Inside positive membrane potential generated by imposing an inwardly directed $K^+$ gradient and valinomycin significantly stimulated the $Na^+-dependent$ $Ca^{2+}$ uptake. These results indicate that a $Na^+-Ca^{2+}$ exchange system exists in the sarcolemmal membranes isolated from cat ileal longitudinal muscle and it might operate as an electrogenic process.

• Applied Chemistry for Engineering
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• v.9 no.6
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• pp.870-877
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• 1998

With impedance spectrum measurements, impedance was studied in the interface between sample solutions for $K^+-ion$ selective PVC membrane electrode containing neutral carriers [dibenzo-18-crown-6 (D18Cr6) and valinomycine (Val)]. Response characteristics of electrode were examined by measuring AC impedance spectra that were resulted from the chemical structure and the content of carrier, variation of plasticizer, membrane thickness, doping of base electrolytes, and concentration variation of sample solution. Transport characteristics of PVC membrane electrode were also studied. It was found that the equivalent circuit for the membrane in $K^+$ solution could be expressed by a series combination of solution resistance and a parallel circuit consisting of the bulk resistance and geometric capacitance of the membrane system. But the charge transfer resistance and Warburg resistance were overlapped a little in the low concentration and low frequency ranges. The carrier, D18Cr6 was best for electrode and impedance characteristics, and ideal electrode characteristics were appeared especially in case of doping of the base electrolyte[potassium tetraphenylborate(TPB)]. The optimum carrier content was about 3.23 wt% in case of D18Cr6 and Val. DBP was best as a plasticizer. As membrane thickness decreased the impedance characteristics was improved, but electrode characteristics were lowered for membrane thickness below the optimum. In the case of D18Cr6, the selectivity coefficients by the mixed solution method for the $K^+$ ion were the order of $NH_4{^+}>Ca^{2+}>Mg^{2+}>Na^+$.