• The Korean Journal of Physiology
• /
• v.29 no.2
• /
• pp.203-216
• /
• 1995

The effects of ${\alpha}_1-adrenergic$ receptor stimulation on membrane potential, intracellular $Na^+$ activity, and twitch force were investigated in ventricular muscles from guinea-pig hearts. Action potentials, intracellular $Na^+$ activity, and twitch force of ventricular papillary muscles were measured simultaneously under various experimental conditions. Stimulation of the ${\alpha}_1-adrenergic$ receptor by phenylephrine produced variable changes in action potential duration, a slight hyperpolarization of the diastolic membrane potential, a decrease in intracellular $Na^+$ activity, and a biphasic inotropic response in which a transient negative inotropic response was followed by a sustained positive inotropic response. These changes were blocked by prazosin, an antagonist of the ${\alpha}_1-adrenergic$ receptor, but not by atenolol, an antagonist of the ${\beta}-adrenergic$ receptor. This indicates that the changes in membrane potential, intracellular $Na^+$ activity, and twitch force are mediated by stimulation of the ${\alpha}_1-adrenergic$ receptor, but not by stimulation of ${\beta}-adrenergic$ receptor. The decrease in intracellular $Na^+$ activity was not observed in quiescent muscles, depending on the rate of the action pontentials in beating muscles. The intracellular $Na^+$ activity decrease was substantially inhibited by tetrodotoxin. However, the decrease in intracellular $Na^+$ activity was not affected by an inhibition of the $Na^+-K^+$ pump. Therefore, the decrease in intracellular $Na^+$ activity mediated by the ${\alpha}_1-adrenergic$ receptor appears to be due to a reduction of $Na^+$ influx during the action potential, perhaps through tetrodotoxin sensitive $Na^+$ channels. Our study also revealed that the decrease in intracellular $Na^+$ activity might be related to the transient negative inotropic response. The intracellular $Na^+$ activity decrease could lower intracellular $Ca^{2+}$ through the $Na^+-Ca^{2+}$ exchanger and thereby produce a decline in twitch force.

• Biomolecules & Therapeutics
• /
• v.25 no.6
• /
• pp.593-598
• /
• 2017

The $Na^+/H^+$ exchanger-1 (NHE-1) is a ubiquitously expressed pH-regulatory membrane protein that functions in the brain, heart, and other organs. It is increased by intracellular acidosis through the interaction of intracellular $H^+$ with an allosteric modifier site in the transport domain. In the previous study, we reported that glutamate-induced NHE-1 phosphorylation mediated by activation of protein kinase C-${\beta}$ (PKC-${\beta}$) in cultured neuron cells via extracellular signal-regulated kinases (ERK)/p90 ribosomal s6 kinases (p90RSK) pathway results in NHE-1 activation. However, whether glutamate stimulates NHE-1 activity solely by the allosteric mechanism remains elusive. Cultured primary cortical neuronal cells were subjected to intracellular acidosis by exposure to $100{\mu}M$ glutamate or 20 mM $NH_4Cl$. After the desired duration of intracellular acidosis, the phosphorylation and activation of PKC-${\beta}$, ERK1/2 and p90RSK were determined by Western blotting. We investigated whether the duration of intracellular acidosis is controlled by glutamate exposure time. The NHE-1 activation increased while intracellular acidosis sustained for >3 min. To determine if sustained intracellular acidosis induced NHE-1 phosphorylation, we examined phosphorylation of NHE-1 induced by intracellular acidosis by transient exposure to $NH_4Cl$. Sustained intracellular acidosis led to activation and phosphorylation of NHE-1. In addition, sustained intracellular acidosis also activated the PKC-${\beta}$, ERK1/2, and p90RSK in neuronal cells. We conclude that glutamate stimulates NHE-1 activity through sustained intracellular acidosis, which mediates NHE-1 phosphorylation regulated by PKC-${\beta}$/ERK1/2/p90RSK pathway in neuronal cells.

• Journal of Korean Society on Water Environment
• /
• v.20 no.6
• /
• pp.692-697
• /
• 2004

Biological phosphorus removal is characterized by complex interactions between different intracellular components of energy as PHA. Therefore, fundamental understanding of the behavior of the intracellular components and their influence on the removal of phosphorus is essential before control strategies to stabilize the proper process. The purpose of this study is to investigate relationship between release of phosphorus and synthesis of intracellular storage polymer. Mass of stored intracellular storage polymer was 21.2 mg PHA/L, 28.8 mg PHA/g MLSS. And phosphorus release/intracellular storage polymer synthesis rate was 1.8545 mg stored polymer/mg Phosphate. In the aerobic phase, mass of PAOs synthesis is 49.37 mg PAOs/L. And PAOs fraction was 6.7-6.9%. Thus intracellular storage polymer synthesis by PAOs is calculated as 493mg PHA/g PAOs.

• The Korean Journal of Physiology and Pharmacology
• /
• v.2 no.4
• /
• pp.411-417
• /
• 1998

The role of phospholipase ($A_2\;PLA_2$) in tumor cell growth was investigated using SK-N-MC human neuroblastoma cells. 4-Bromophenacyl bromide (BPB) and mepacrine (Mep), known $PLA_2$ inhibitors, suppressed growth of the tumor cells in a dose-dependent manner without a significant cytotoxicity. Melittin (Mel), a $PLA_2$ activator, enhanced the cell growth in a concentration-dependent fashion. The growth-enhancing effects of Mel were significantly reversed by the co-treatment with $PLA_2$ inhibitors. In addition, Mel induced intracellular $Ca^{2+}$ release from internal stores like as did serum, a known intracellular $Ca^{2+}$ agonist in the tumor cells. Intracellular $Ca^{2+}$ release induced by these agonists was significantly blocked by $PLA_2$ inhibitors at growth-inhibitory concentrations. Arachidonic acid (AA), a product of the $PLA_2-catalyzed$ reaction, induced cell growth enhancement and intracellular $Ca^{2+}$ release. These effects of AA were significantly blocked by BAPTA/AM, an intracellular $Ca^{2+}$ chelator. Taken together, these results suggest that the modulation of $PLA_2$ activity may be one of the regulatory mechanisms of cell growth in human neuroblastoma cells. Intracellular $Ca^{2+}$ may act as a key mediator in the $PLA_2-induced$ growth regulation.

• The Korean Journal of Physiology and Pharmacology
• /
• v.18 no.3
• /
• pp.241-247
• /
• 2014

To investigate the underlying mechanisms of C18 fatty acids (stearic acid, oleic acid, linoleic acid and ${\alpha}$-linolenic acid) on mast cells, we measured the effect of C18 fatty acids on intracellular $Ca^{2+}$ mobilization and histamine release in RBL-2H3 mast cells. Stearic acid rapidly increased initial peak of intracellular $Ca^{2+}$ mobilization, whereas linoleic acid and ${\alpha}$-linolenic acid gradually increased this mobilization. In the absence of extracellular $Ca^{2+}$, stearic acid ($100{\mu}M$) did not cause any increase of intracellular $Ca^{2+}$ mobilization. Both linoleic acid and ${\alpha}$-linolenic acid increased intracellular $Ca^{2+}$ mobilization, but the increase was smaller than that in the presence of extracellular $Ca^{2+}$. These results suggest that C18 fatty acid-induced intracellular $Ca^{2+}$ mobilization is mainly dependent on extracellular $Ca^{2+}$ influx. Verapamil dose-dependently inhibited stearic acid-induced intracellular $Ca^{2+}$ mobilization, but did not affect both linoleic acid- and ${\alpha}$-linolenic acid-induced intracellular $Ca^{2+}$ mobilization. These data suggest that the underlying mechanism of stearic acid, linoleic acid and ${\alpha}$-linolenic acid on intracellular $Ca^{2+}$ mobilization may differ. Linoleic acid and ${\alpha}$-linolenic acid significantly increased histamine release. Linoleic acid (C18:2: ${\omega}$-6)-induced intracellular $Ca^{2+}$ mobilization and histamine release were more prominent than ${\alpha}$-linolenic acid (C18:3: ${\omega}$-3). These data support the view that the intake of more ${\alpha}$-linolenic acid than linoleic acid is useful in preventing inflammation.

• The Korean Journal of Physiology and Pharmacology
• /
• v.1 no.5
• /
• pp.537-546
• /
• 1997

It has been postulated that the intracellular taurine is co-transported with $Na^+$down a concentration gradient and prevents the intracellular accumulation of sodium. It is therefore, expected that an elevated level of intracellular taurine prevents the sodium-promoted calcium influx to protect the cellular damages associated with sodium and calcium overload. In the present study, we evaluated the effects of intra- and extracellular taurine on the myocardial $Na^+$and$Ca^{++}$ contents and the cardiac functions in isolated rat hearts which were loaded with sodium by monensin, a $Na^+-ionophore$. Monensin caused a dose-dependent increase in intracellular $Na^+$ accompanied with a subsequent increase in intracellular $Ca^{++}$ and a mechanical dysfunction. In this monensin-treated heart, myocardial taurine content was decreased with a concomittent increase in the release of taurine. The monensin-induced increases in intracellular $Na^+$, $Ca^{++}$ and depression of cardiac function were prevented in the hearts of which taurine content had been increased by high-taurine diet. Conversely, in the hearts of which taurine concentration gradient had been decreased by addition of taurine in the perfusate, the monensin-induced increases in $Na^+$, $Ca^{++}$ and functional depression were accelerated. These results suggest that taurine, depending on the intra-extracellular concentration gradient, can affect intracellular sodium and calcium concentrations, and that an increased intracellular taurine may play a role in protection of myocardial dysfunction associated with the sodium and calcium overload.

• Archives of Pharmacal Research
• /
• v.21 no.6
• /
• pp.664-670
• /
• 1998

The role of intracellular $Ca^{2+}$, in the regulation of tumor cell proliferation by products of arachidonic acid (AA) metabolism was investigated using U-373 MG human as trocytoma cells. Treatment with nordihydroguaiaretic acid (NDGA), a lipoxygenase (LOX) inhibitor, or caffeic acid (CA), a specific 5-LOX inhibitor, suppressed proliferation of the tumor cells in a dose-dependent manner. However, indomethacin (indo), a cyclooxygenase (COX) inhibitor, did not significantly alter proliferation of the tumor cells. At anti-proliferative concentrations, NDGA and CA significantly inhibited intracellular $Ca^{2+}$ release induced by carbachol, a known intracelluar $Ca^{2+}$ agonist in the tumor cells. Exogenous administration of leukotriene $B_4(LTB_4)$, an AA metabolite of LOX pathway, enhanced proliferation of the tumor cells in a concentration-dependent fashion. In addition, $LTB_4$, induced intracelluar $Ca^{2+}$ release. Intracellular $Ca^{2+}$-inhibitors, such as an intracellular $Ca^{2+}$ chelator (BAPTA) and intracellular $Ca^{2+}$-release inhibitors (dantrolene and TMB-8), significantly blocked the LTB4-induced enhancement of cell proliferation and intracellular $Ca^{2+}$ release. These results suggest that LOX activity may be critical for cell proliferation of the human astrocytoma cells and that intracelluar $Ca^{2+}$ may play a major role in the mechanism of action of LOX.

• Korean Journal of Environmental Biology
• /
• v.21 no.3
• /
• pp.303-307
• /
• 2003

Tributyltin (TBT) used world-wide in antifouling paints toy ships is a wide-spread environmental pollutant. At low doses, antiproliferative modes of action have been shown to be involved, whereas at higher doses apoptosis seems to be the mechanism of toxicity in reproductive organs by TBT. In this study, we investigated that the mechanisms underlying apoptosis induced by TBT in R2C cell. Effects of TBT on intracellular $Ca^{2+}$ level and reactive oxygen species (ROS) were investigated in R2C cells by fluorescence detector. TBT significantly induced intracellular $Ca^{2+}$ level in a time-dependent manner. The rise in intracellular $Ca^{2+}$ level was followed by a time-dependent generation of reactive oxygen species (ROS) at the cytosol level. Simultaneously, TBT induced the release of cytochrome c from the mitochondrial membrane into the cytosol. Furthermore, ROS production and the release of cytochrome c were reduced by BAPTA, an intracellular $Ca^{2+}$ chelator, indicating the important role of $Ca^{2+}$ in R2C during these early intracellular events. In addition, Z-DEVD FMB, a caspase -3 inhibitor, decreased apoptosis by TBT. Taken together, the present results indicated that the apoptotic pathway by TBT might start with an increase in intracellular $Ca^{2+}$ level, continues with release of ROS and cytochrome c from mitochondria, activation of caspases, and finally results in DNA fragmentation.

• BMB Reports
• /
• v.28 no.5
• /
• pp.392-397
• /
• 1995

The effect of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) on the intracellular $Ca^{2+}$ level was studied in NIH3T3 fibroblast cells. A reduction of the intracellular $Ca^{2+}$ level was observed after exposure to 300 ${\mu}m$ MNNG. However, the intracellular level of $IP_3$, a well-known regulator of $Ca^{2+}$ release from internal storage, was not changed by MNNG treatment. Instead, a reduction of the intracellular NAD level was observed. NAD as well as $IP_3$ stimulated intracellular $Ca^{2+}$ release from permeabilized cells. The treatment of 3-aminobenzamide, which inhibited the MNNG-induced reduction of the NAD level, also prevented the MNNG-induced decrease of the $Ca^{2+}$ level. Our data suggest that MNNG reduces the intracellular $Ca^{2+}$ level by NAD depletion in NIH3T3 cells.

• Archives of Pharmacal Research
• /
• v.27 no.12
• /
• pp.1245-1252
• /
• 2004

Although ascorbate (vitamin C) has been shown to have anti-cancer actions, its effect on human hepatoma cells has not yet been investigated, and thus, the exact mechanism of this action is not fully understood. In this study, the mechanism by which ascorbate induces apoptosis using HepG2 human hepatoblastoma cells is investigated. Ascorbate induced apoptotic cell death in a dose-dependent manner in the cells, was assessed through flow cytometric analysis. Contrary to expectation, ascorbate did not alter the cellular redox status, and treatment with antioxidants (N-acetyl cysteine and N,N-diphenyl-p-phenylenediamine) had no influence on the ascorbate-induced apoptosis. However, ascorbate induced a rapid and sustained increase in intracellular $Ca^{2+}$ concentration. EGTA, an extracellular $Ca^{2+}$ chelator did not significantly alter the ascorbate-induced intracellular $Ca^{2+}$ increase and apoptosis, whereas dantrolene, an intracellular $Ca^{2+}$ release blocker, completely blocked these actions of ascorbate. In addition, phospholipase C (PLC) inhibitors (U-73122 and manoalide) significantly suppressed the intracellular $Ca^{2+}$ release and apoptosis induced by ascorbate. Collectively, these results suggest that ascorbate induced apoptosis without changes in the cellular redox status in HepG2 cells, and that the PLC-coupled intracellular $Ca^{2+}$ release mechanism may mediate ascorbate-induced apoptosis.