• 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.

• Proceedings of the Korean Society of Applied Pharmacology
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• 2003.11a
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• pp.106-106
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• 2003

Choline serves critical roles in the CNS both as a precursor of neurotransmitter and as an essential component of membrane phospholipids. The long-term maintenance of brain choline concentration is dependent on choline transport across the blood-brain barrier (BBB), And, we examined to elucidate the characteristics of transport of choline across the BBB using conditionally immortalized rat brain capillary endothelial cell line (TR-BBB) in vitro. The ［$^3$H］choline in TR - BBB was increased by time dependently, but independent on Na$\^$＋/, and the transport process is saturable with Michaelis-Menten constrant, Km of about 26 ${\mu}$M. The uptake of ［$^3$H］choline is susceptible for inhibition by various organic cationic compounds including hemicholinium-3, tetraethylammonium chloride (TEA) and $\ell$-carnitine. Also, we investigated the relationship of transport of choline and cationic drugs. The uptake of ［$^3$H］choline is inhibited by antioxidant, a-phenyl-n-tert-butyl nitrone (PBN) with IC$\sub$50/ of 1.2 mM. and by Alzheimer's disease therapeutics, such as acetyl $\ell$-carnitine, tacrine and donepezil. Also, choline uptake presented competitive inhibition with PBN, donepezil and acetyl $\ell$-carnitine in Lineweaver-Burk plot. In conclusion, TR-BBB cells express a saturable transport system for uptake of choline, and several cationic drugs may be transported into the brain by BBB choline transporter.

• The Korean Journal of Physiology
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• v.23 no.1
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• pp.23-34
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• 1989

Gentamicin (GM) is a polybasic, aminoglycoside antibiotic used frequently for the treatment of serious gram-negative infections. The major limiting factors in the clinical use of GM as well as other aminoglycoside antibiotics are their nephrotoxicity and ototoxicity. The primary mechanism of cell injury in aminoglycoside toxicity appears to be the disruption of normal membrane function and the inhibition of $Na^{+}-K^{+}$ ATPase activity. There are both indirect and direct evidences which suggests that the effect of aminoglycoside antibiotics on $Na^{+}-K^{+}$ ATPase may explain, or contribute to, their toxicity. It has been shown that aminoglycoside reduce total ATPase activity (Kaku et al., 1973) and $Na^{+}-K^{+}$ ATPase activity (linuma et al., 1967) in the stria vascularis and spiral ligament of the guinea-pig cochlea. Lipsky and Lietman (1980) reported that aminoglycoside antibitoics inhibited the activity of $Na^{+}-K^{+}$ ATPase in microsomal fractions of the cortex and medulla of the guinea-pig kidney, isolated rat renal tubule and human erythrocyte ghosts. The present invstigation was undertaken to elucidate the mechanism of GM on human erythrocytes by examining its effect on $Na^{+}-K^{+}$ ATPase activity, actives sodium and potassium transport across red blood cell and $^{3}H-ouabain$ binding to red blood cell membranes. The results obtained are summarized as follows: 1) CM inhibited significantly both the activity of total ATPase and $Na^{+}-K^{+}$ ATPase at all concentrations tested. 2) GM inhibited active $^{22}Na$ efflux across red blood cell. When ouabain is present, the rate of $^{22}Na$ efflux was completely inhibited. When both GM and ouabain were added, the inhibitory effect of active $^{22}Na$ efflux was more pronounced. 3) Active $^{86}Rb$ influx was inhibited significantly by GM. In the presence of ouabain, the rate of $^{86}Rb$ influx is markedly inhibited. But $^{86}Rb$ influx is not appreciably altered by the presence of both GM and ouabain. 4) In the presence of GM, $^{3}H-ouabain$ binding to red blood cell membrane increased. From the above results, it may be concluded that the inhibition of active sodium and potassium transport across red blood cell by gentamicin appears to be due to the inhibition of $Na^{+}-K^{+}$ ATPase activity and an increase in ouabain binding to red blood cell membranes.

• Journal of Korean Academy of Nursing
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• v.13 no.2
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• pp.87-104
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• 1983

It has been well documented that animals exposed to cold show increased activity of thyroid gland. The calorigenic action of thyroid hormone has been demonstrated by a variety of in vivo and in vitro studies. According to Edelman et al., the thyroid thermogenesis is due to activation of energy consuming processes, especially the active sodium transport by the hormone in target tissues. If so, the increase in thyroid activity during cold exposure should induce increased capacity of sodium transport in target tissue and the change in tissue metabolism should be precisely correlated with the change in Na+_K+_ATPase activity of the tissue. This possibility was tested in the present study: in one series, changes in oxygen consumption and Na+_K+_-ATPase activity of liver preparations were measured in rats as a function of thyroid status, in order to establish the effect of thyroid hormone on the tissue respiration and enzyme system in another series, the effect of cold stimulus on the serum thyroid hormone level, hepatic tissue oxygen consumption and Na+_K+_ATPase activity in rats. The results obtained are as follows: 1. The Na+_dependent oxygen consumption of liver slices, the oxygen consumption of liver mitochondria and the Na+_K+_ATPase activity of liver preparations were significantly inhibited in hypothyroidism and activated in hyperthyroidism. Kinetic analysis indicated that the Vmax. of Na+_K+_ATPase was decreased in hypothyroidism and increased in hyperth)'roidism. 2. In cold exposed rats, the serum triiodothyronine (T₃) level increased rapidly during the initial one day of cold exposure, then declined slowly to the control level after two weeks. The serum thyroxine (T₄) level decreased gradually throughout the cold exposure. Accordingly the T₃/T₄ratio increased. The mitochondrial oxygen consumption and the Na+_dependent oxygen consumption of liver slices increased during the first two days and then remained unchanged thereafter The activity of the Na+_K+_ATPase in liver preparations increased during cold exposure with a time course similar to that of oxygen consumption. Kinetic analysis indicated that the Vmax. of Na+_K+_ATPase increased. 3. Once the animal was adapted to cold, induction of hypothyroidism did not significantly alter the hepatic oxygen consumption and Na+_K+_ATPase activity. These results indicate that: 1) thyroid hormone increases capacities of mitochondrial respiration and active sodium transport in target tissues such as liver; 2) the increased T₃level during the initial period of cold exposure facilitates biosynthesis of Na+_K+_ATPase and mitochondrial enzymes for oxidative phosphorylation, leading to enhanced production and utilization of ATP, hence heat production.

• The Korean Journal of Physiology
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• v.25 no.2
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• pp.179-188
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• 1991

Effect of a sulfhydryl reagent, p-chloromercuribenzoic acid (PCMB), on the transport of succinate was studied in brush border (BBMV) and basolateral (BLMV) membrane vesicles isolated from rabbit renal cortex. PCMB induced an irreversible inhibition of the $Na^+-dependent$ succinate uptake in a dose-dependent manner with $IC_{50}$ of 55 and $65\;{\mu}M$ in BBMV and BLMV, respectively. The inhibitory effect of PCMB was prevented by a pretreatment of vesicles with dithiothreitol. PCMB did not increase $Na^+$ permeability at concentrations inhibiting succinate uptake. The PCMB inhibition of succinate uptake was due to a change in Vmax, but not in Km. When membrane vesicles were pretreated with PCMB in the presence of unlabelled succinate, the inhibitory effect was significantly reduced. In both BBMV and BLMV, succinate uptake was inhibited by various sulfhydryl reagents with the inhibitory potency of following order: $HgCl_2$>DTNB>PCMBS>PCMB. These results suggest that sulfhydryl groups are essential for dicarboxylate transport and that they may be located at or near substrate binding sites of the transporters in renal brush border and basolateral membranes.

• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.839-842
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• 2012

We report for the first time the synthesis of niobium dioxide nanowires on a sapphire substrate by chemical vapor transport method. We identified single crystalline nature of as-synthesized nanowires by scanning electron microscopy and transmission electron microscopy. Niobium dioxide nanowires with their large surface-to-volume ratio and high activities can be employed for electrochemical catalysts and immunosensors. The Raman spectrum of niobium dioxide nanowires also confirmed their identity.

• BMB Reports
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• v.39 no.4
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• pp.394-399
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• 2006

The transport of putrescine into a moderately salt tolerant cyanobacterium Synechocystis sp. PCC 6803 was characterized by measuring the uptake of radioactively-labeled putrescine. Putrescine transport showed saturation kinetics with an apparent $K_m$ of $92{\pm}10\;{\mu}M$ and $V_{max}$ of $0.33{\pm}0.05\;nmol/min/mg$ protein. The transport of putrescine was pH-dependent with highest activity at pH 7.0. Strong inhibition of putrescine transport was caused by spermine and spermidine whereas only slight inhibition was observed by the addition of various amino acids. These results suggest that the transport system in Synechocystis sp. PCC 6803 is highly specific for polyamines. Putrescine transport is energy-dependent as evidenced by the inhibition by various metabolic inhibitors and ionophores. Slow growth was observed in cells grown under salt stress. Addition of low concentration of putrescine could restore growth almost to the level observed in the absence of salt stress. Upshift of the external osmolality generated by either NaCl or sorbitol caused an increased putrescine transport with an optimum 2-fold increase at 20 mosmol/kg. The stimulation of putrescine transport mediated by osmotic upshift was abolished in chloramphenicol-treated cells, suggesting possible involvement of an inducible transport system.

• The Korean Journal of Physiology and Pharmacology
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• v.11 no.2
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• pp.71-77
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• 2007

Cisplatin treatment increases the excretion of inorganic phosphate in vivo. However, the mechanism by which cisplatin reduces phosphate uptake through renal proximal tubular cells has not yet been elucidated. We examined the effect of cisplatin on $Na^+$-dependent phosphate uptake in opossum kidney (OK) cells, an established proximal tubular cell line. Cells were exposed to cisplatin for an appropriate time period and phosphate uptake was measured using $[^{32}P]$-phosphate. Changes in the number of phosphate transporter in membranes were evaluated by kinetic analysis, $[^{14}C]$phosphonoformic acid binding, and Western blot analysis. Cisplatin inhibited phosphate uptake in a time- and dose-dependent manner, and also the $Na^+$-dependent uptake without altering $Na^+$-independent uptake. The cisplatin inhibition was not affected by the hydrogen peroxide scavenger catalase, but completely prevented by the hydroxyl radical scavenger dimethylthiourea. Antioxidants were ineffective in preventing the cisplatin-induced inhibition of phosphate uptake. Kinetic analysis indicated that cisplatin decreased Vmax of $Na^+$-dependent phosphate uptake without any change in the Km value. $Na^+$-dependent phosphonoformic acid binding was decreased by cisplatin treatment. Western blot analysis showed that cisplatin caused degradation of $Na^+$-dependent phosphate transporter protein. Taken together, these data suggest that cisplatin inhibits phosphate transport in renal proximal tubular cells through the reduction in the number of functional phosphate transport units. Such effects of cisplatin are mediated by production of hydroxyl radicals.

• The Korean Journal of Physiology and Pharmacology
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• v.3 no.1
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• pp.83-91
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• 1999

Angiotensin II (ANG II) has a biphasic effect on $Na^+$ transport in proximal tubule: low doses of ANG II increase the $Na^+$ transport, whereas high doses of ANG II inhibit it. However, the mechanisms of high dose ANG II-induced inhibition on $Na^+$ uptake are poorly understood. Thus the aim of the present study was to investigate signal transduction pathways involved in the ANG II-induced inhibition of $Na^+$ uptake in the primary cultured rabbit renal proximal tubule cells (PTCs) in hormonally defined serum-free medium. ANG II $(10^{-9}\;M)-induced$ inhibition of $Na^+$ uptake was blocked by losartan $(10^{-8}\;M,\;AT_1\;antagonist),$ but not by PD123319 $(10^{-8}\;M,\;AT_2\;antagonist)$ (P<0.05). ANG II-induced inhibition of $Na^+$ uptake was also completely abolished by neomycin $(10^{-4}\;M,$ PLC inhibitor), W-7 $(10^{-4}\;M,$ calmodulin antagonist), and $AACOCF_3\;(10^{-6}\;M,\;PLA_2\;inhibitor)$ (P<0.05). ANG II significantly increased $[^3H]arachidonic$ acid (AA) release compared to control. The ANG II-induced $[^3H]AA$ release was blocked by losartan, $AACOCF_3,$ neomycin, and W-7, but not by PD123319. ANG II-induced $[^3H]AA$ release in the presence of extracellular $Ca^{2+}$ was greater than in $Ca^{2+}-free$ medium, and it was partially blocked by TMB-8 $(10^{-4}\;M,$ intracelluar $Ca^{2+}$ mobilization blocker). However, in the absence of extracellular $Ca^{2+},$ it was completely blocked by TMB-8. In addition, econazole $(10^{-6}\;M,$ cytochrome P-450 monooxygenase inhibitor) and indomethacin $(10^{-6}\;M,$ cyclooxygenase inhibitor) blocked ANG II-induced inhibition of $Na^+$ uptake, but NGDA $(10^{-6}\;M,$ lipoxygenase inhibitor) did not affect it. In conclusion, $PLA_2-mediated$ AA release is involved in ANG II-induced inhibition of $Na^+$ uptake and is modulated by $[Ca^{2+}]_i$ in the PTCs.

• The Korean Journal of Pharmacology
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• v.30 no.3
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• pp.313-319
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• 1994

This study was undertaken to investigate the relationship between the $Na^+$ channels of the cardiovascular regulation center and the responses to increased $Na^+$ concentration in the cerebrospinal fluid (CSF), by observing the effects of icv administration of the agents affecting $Na^+$ transport. Icv infusion of $200\;{\mu}l$ of 1 M NaCl produced hypertension and bradycardia in the urethane-anesthetized rabbit, and the bradycardia was inhibited and reversed to tachycardia by vagotomy. Amiloride, a $Na^+$ transport inhibitor, produced hypertension and bradycardia, which were not altered by vagotomy, and it did not affect the NaCl-induced responses. Benzamil, a derivative of amiloride with higher specificity, neither produced any cardiovascular effects by itself, nor affected the NaCl-induced responses. In vagotomized rabbits, icv amiloride reversed the NaCl-induced tachycardia to a bradycardia, but the bradycardiac effect was not altered by pretreating with NaCl. This study showed that although amiloride and benzamil slightly differ in their cardiovascular action, neither of them did affect the NaCl-induced responses. We suggest that the $Na^+$ channels which are sensitive to amiloride or benzamil in the cardiovascular regulation center are not involved in the NaCl-induced response.