• The Korean Journal of Physiology and Pharmacology
• /
• v.3 no.2
• /
• pp.137-146
• /
• 1999

Interactions among dexamethasone, dehydroepiandrosterone (DHEA), lipopolysaccharide (LPS), and antimycin A on the glutamate uptake and the polyamine uptake were investigated in primary cultures of rat cerebral cortical astrocytes to examine the effects of dexamethasone and DHEA on the regulatory role of astrocytes in conditions of increased extracellular concentrations of glutamate or polyamines. 1. $[^3H]Glutamate$ uptake: LPS and antimycin A decreased $V_{max},$ but both drugs had little effect on $K_m.$ Dexamethasone also decreased basal $V_{max}$ without any significant effect on $K_m.$ And dexamethasone further decreased the antimycin A-induced decrease of $V_{max}.$ DHEA did not affect the kinetics of basal glutamate uptake and the change by LPS or antimycin A. 2. $[^{14}C]Putrescine$ uptake: LPS increased $V_{max},$ and antimycin A decreased $V_{max}.$ They showed little effect on $K_m.$ Dexamethasone decreased $V_{max}$ of basal uptake and further decreased the antimycin A-induced decrease of $V_{max},$ and also decreased $V_{max}$ to less than control in LPS-treated astrocytes. DHEA did not affect $K_m$ and the change of $V_{max}$ by LPS or antimycin A. 3. $[^{14}C]Spermine$ uptake: Antimycin A decreased $V_{max},$ and LPS might increase $V_{max}.\;K_m$ was little affected by the drugs. Dexamethasone decreased basal $V_{max}$ and might further decrease the antimycin A-induced decrease of $V_{max}.$ And dexamethasone also decreased $V_{max}$ to less than control in LPS-treated astrocytes. DHEA might increase basal $V_{max}$ and $V_{max}$ of LPS-treated astrocytes. 4. $V_{max}$ of glutamate uptake by astrocytes was increased by putrescine (1000 ${\mu}M$ & 2000 ${\mu}M$) and spermidine (200 ${\mu}M,$ 500 ${\mu}M$ & 2000 ${\mu}M$). Spermine, 200 ${\mu}M$ (and 100 ${\mu}M$), also increased $V_{max},$ but a higher dose of 2000 ${\mu}M$ decreased $V_{max}.\;K_m$ of glutamate uptake was not significantly changed by these polyamines, except that higher doses of spermine showed tendency to decrease $K_m$ of glutamate uptake. In astrocytes, dexamethasone inhibited the glutamate uptake and the polyamine uptake in normal or hypoxic conditions, and the polyamine uptake might be stimulated by LPS and DHEA. Polyamines could aid astrocytes to uptake glutamate.

• Journal of Microbiology and Biotechnology
• /
• v.19 no.5
• /
• pp.447-454
• /
• 2009

The transport of spermidine into a cyanobacterium, Synechocystis sp. pec 6803, was characterized by measuring the uptake of $^{14}C$-spermidine. Spermidine transport was shown to be saturable with an apparent affinity constant ($K_m$) value of $67{\mu}M$ and a maximal velocity ($V_{max}$) value of 0.45 nmol/min/mg protein. Spermidine uptake was pH-dependent with the pH optimum being 8.0. The competition experiment showed strong inhibition of spermidine uptake by putrescine and spermine, whereas amino acids were hardly inhibitory. The inhibition kinetics of spermidine transport by putrescine and spermine was found to be noncompetitive with $K_i$ values of 292 and $432{\mu}M$, respectively. The inhibition of spermidine transport by various metabolic inhibitors and ionophores suggests that spermidine uptake is energy-dependent. The diminution of cell growth was observed in cells grown at a high concentration of NaCl. Addition of a low concentration of spermidine at 0.5 mM relieved growth inhibition by salt stress. Upshift of the external osmolality generated by either NaCl or sorbitol caused an increased spermidine transport with about 30-40% increase at 10 mosmol/kg upshift.

• Molecules and Cells
• /
• v.20 no.1
• /
• pp.127-135
• /
• 2005

The uptake of putrescine, spermidine and spermine by Fortner's hamster amelanocytic melanoma AMEL-3 cells was observed in this study to be time-dependent, temperature-sensitive, pH-dependent and saturable. Metabolic poisons nullified polyamine uptake, an indication that this is an energy-requiring mechanism. The presence of $Na^+$ ions was found to be requisite to full activity. Valinomycin, gramicidin, monensin and the calcium ionophore calcimycin were also observed to inhibit the process substantially. The transporter active site would seem to contain sulfhydryl groups. Other diamines and polyamine analogues, as well as cationic diamidines, suppressed putrescine uptake. The presence of the ornithine decarboxylase inhibitor DFMO in the culture medium induced putrescine inflows. Putrescine, in turn, induced the negative expression of the carrier, thus suggesting that this influx mechanism is governed by up/down regulation. The cationic diamidine CGP 40215A and its analogue CGP039937A competitively inhibited putrescine transport, with Ki values of 1.9 and $15{\mu}M$, respectively. The role of polyamine uptake in these cultures is discussed.

• The Korean Journal of Pharmacology
• /
• v.32 no.1
• /
• pp.113-123
• /
• 1996

It has been well known that polyamines ensure the stability of chromatin structure and the fidelity of DNA transcription. This study was carried out to evaluate the effect of polyamines on the apoptosis of mouse thymocytes induced by dexamethasone and polyamine synthesis inhibitors. 1) In the histological death findings of thymocytes double-stained with acridine orange and ethidium bromide, the apoptotic and the necrotic fractions (AF; NF) in the control group were $9.4{\pm}4.2%$ and $4.5{\pm}5.3%$, respectively. Dexamethasone $(3\;{\times}\;10^{-8}\;M:\;DX)$ in creased AF upto $52.0{\pm}8.1%$ and did not change NF, but A23187 $(5\;{\times}\;10^{-7}\;M:\;A2)$ increased AF and NF upto $45.0{\pm}8.9%$ and $20.5{\pm}10.6%$, respectively. 2) The thymocyte viability was significantly reduced by DX, DHEA $(1\;{\times}\;10^{-4}\;M)$, A2, DFMO $(1\;{\times}\;10^{-4}\;M)$, and $MGBG\;(1\;{\times}\;10^{-4}\;M)$, respectively. It was, however, little affected by $aminoguanidine\;(1\;{\times}\;10^{-4}\;M:\;AG)$, $putrescine\;(1\;{\times}\;10^{-5}\;M:\;PT)$, $spermidine\;(1\;{\times}\;10^{-5}\;M:\;SD)$, and $spermine\;(1\;{\times}\;10^{-5}\;M:\;SM)$. 3) The genomic DNA of mouse thymocyte was markedly fragmented by DX and A2, respectively, and to a lesser extent, by DHEA, but was little affected by MGBG, DFMO, AG, and each of polyamines. 4) The DX induced reduction of thymocyte viability was moderately attenuated by DHEA, but little affected by DFMO, MGBC, and AG. However, SM significantly attenuated the viability reduction induced by A2 as well as DX. 5) The thymocyte viability reduction by MGBG and DFMO was significantly attenuated by only SM among three polyamines applied in this study. 6) The thymocyte viability redution by combined treatments of DX with DFMO and MGBG, respectively, was significantly attenuated by SM, and moderately by PT. But the viability reduction by combined treatment of DX with AG or DHEA was not affected by polyamines. These results suggest that polyamines, particularly spermine, might play the inhibitory role in thymocyte apoptosis and the inhibitory effect can be ascribed in part to the increase of polyamine uptake by thymocytes pretreated with DFMO and MGBG.

• Biomolecules & Therapeutics
• /
• v.5 no.3
• /
• pp.265-271
• /
• 1997

Since the advent of chemotherapy, certain types of cancer have been particularly resistant to chemotherapeutic treatment. One of the most well-studied types of resistance is resistance to multiple struc-turally dissimialr hydrophobic chemotherapeutic agents, or multidrug resistance (MDR). We found that MDR cells (KBV20C, KB7D) being highly resistant to colchicine, etoposide, and vincristine were found to have very low level of putrescine and low level of spermidine than the drug sensitive parental cells (KB) but they had almost same level of spermine as the drug sensitive cells. Although both MDR and drug sensitive cells had almost same rate of polyamine uptake, MDR cells were much more sensitive to an inhibitor of polyamine synthesis, methylglyoxal-bis guanylhydrazone (MGBG), suggesting that MDR cells might be defective in polyamine synthesis. These results also suggest that HGBG can be used for treatment of MDR in vivo.

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