• Journal of Microbiology and Biotechnology
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• 제18권12호
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• pp.1997-2003
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• 2008

Cordyceps militaris is well known as a traditional medicinal mushroom and has been shown to exhibit immunostimulatory and anticancer activities. In this study, we investigated the apoptosis induced by an aqueous extract of C. militaris (AECM) via the activation of caspases and altered mitochondrial membrane permeability in human breast cancer MDA-MB-231 cells. Exposure to AECM induced apoptosis, as demonstrated by a quantitative analysis of nuclear morphological change and a flow cytometric analysis. AECM increased hyperpolarization of mitochondrial membrane potential and promoted the activation of caspases. Both the cytotoxic effect and apoptotic characteristics induced by AECM treatment were significantly inhibited by z-DEVD-fmk, a caspase-3 inhibitor, which demonstrates the important role of caspase-3 in the observed cytotoxic effect. AECM-induced apoptosis was associated with the inhibition of Akt activation in a time-dependent manner, and pretreatment with LY294002, a PI3K/Akt inhibitor, significantly increased AECM-induced apoptosis. The results indicated that AECM-induced apoptosis may relate to the activation of caspase-3 and mitochondria dysfunctions that correlate with the inactivation of Akt.

• The Korean Journal of Physiology and Pharmacology
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• 제20권5호
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• pp.525-531
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• 2016

The analgesic mechanism of opioids is known to decrease the excitability of substantia gelatinosa (SG) neurons receiving the synaptic inputs from primary nociceptive afferent fiber by increasing inwardly rectifying $K^+$ current. In this study, we examined whether a ${\mu}$-opioid agonist, [D-Ala2,N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO), affects the two-pore domain $K^+$ channel (K2P) current in rat SG neurons using a slice whole-cell patch clamp technique. Also we confirmed which subtypes of K2P channels were associated with DAMGO-induced currents, measuring the expression of K2P channel in whole spinal cord and SG region. DAMGO caused a robust hyperpolarization and outward current in the SG neurons, which developed almost instantaneously and did not show any time-dependent inactivation. Half of the SG neurons exhibited a linear I~V relationship of the DAMGO-induced current, whereas rest of the neurons displayed inward rectification. In SG neurons with a linear I~V relationship of DAMGO-induced current, the reversal potential was close to the $K^+$ equilibrium potentials. The mRNA expression of TWIK (tandem of pore domains in a weak inwardly rectifying $K^+$ channel) related acid-sensitive $K^+$ channel (TASK) 1 and 3 was found in the SG region and a low pH (6.4) significantly blocked the DAMGO-induced $K^+$ current. Taken together, the DAMGO-induced hyperpolarization at resting membrane potential and subsequent decrease in excitability of SG neurons can be carried by the two-pore domain $K^+$ channel (TASK1 and 3) in addition to inwardly rectifying $K^+$ channel.

• The Korean Journal of Physiology and Pharmacology
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• 제15권5호
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• pp.279-283
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• 2011

Quercetin (3,3',4',5,7-pentahydroxyflavone) is an attractive therapeutic flavonoid for cancer treatment because of its beneficial properties including apoptotic, antioxidant, and antiproliferative effects on cancer cells. However, the exact mechanism of action of quercetin on ion channel modulation is poorly understood in bladder cancer 253J cells. In this study, we demonstrated that large conductance $Ca^{2+}$-activated $K^+$ ($BK_{Ca}$) or MaxiK channels were functionally expressed in 253J cells, and quercetin increased $BK_{Ca}$ current in a concentration dependent and reversible manner using a whole cell patch configuration. The half maximal activation concentration ($IC_{50}$) of quercetin was $45.5{\pm}7.2{\mu}m$. The quercetin-evoked $BK_{Ca}$ current was inhibited by tetraethylammonium (TEA; 5 mM) a non-specific $BK_{Ca}$ blocker and iberiotoxin (IBX; 100 nM) a $BK_{Ca}$-specific blocker. Quercetin-induced membrane hyperpolarization was measured by fluorescence-activated cell sorting (FACS) with voltage sensitive dye, bis (1,3-dibutylbarbituric acid) trimethine oxonol ($DiBAC_4$2(3); 100 nM). Quercetin-evoked hyperpolarization was prevented by TEA. Quercetin produced an antiproliferative effect ($30.3{\pm}13.5%$) which was recovered to $53.3{\pm}10.5%$ and $72.9{\pm}3.7%$ by TEA and IBX, respectively. Taken together our results indicate that activation of $BK_{Ca}$ channels may be considered an important target related to the action of quercetin on human bladder cancer cells.

• The Korean Journal of Physiology
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• 제29권2호
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• pp.233-241
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• 1995

The nonapeptide bradykinin has been shown to exhibit an array of biological activities including relaxation/contraction of various smooth muscles. In order to investigate the effects of bradykinin on the contractility and the electrical activity of antral circular muscle of guinea-pig stomach, the isometric contraction and membrane potential were recorded. Also, using standard patch clamp technique, the $Ca^{2+}-activated$ K currents were recorded to observe the change in cytosolic $Ca^{2+}$ concentration. $0.4 {\mu}M$ bradykinin induced a triphasic contractile response (transient contraction-transient relaxation-sustained contraction) and this response was unaffected by pretreatment with neural blockers (tetrodotoxin, atropine and guanethidine) or with apamin. Bradykinin induced hyperpolarization of resting membrane potential and enhanced the amplitude of slow waves and spike potentials. The enhancement of spike potentials was blocked by neural blockers. Both the bradykinin-induced contractions and changes in membrane potential were reversed by the selective $B_2$-receptor antagonist $(N{\alpha}-adamantaneacetyl-_{D}-Arg-[Hyp, Thy,_{D}-Phe]-bradykinin)$. In whole-cell patch clamp experiment, we held the membrane potential at -20 mV and spontaneous and transient changes of Ca-activated K currents were recorded. Bradykinin induced a large transient outward current, consistent with a calcium-releasing action of bradykinin front the intracellular calcium pool, because such change was blocked by pretreatment with caffeine. Bradykinin-induced contraction was also blocked by pretreatment with caffeine. From these results, it is suggested that bradykinin induces a calciumrelease and contraction through the $B_{2}$ receptor of guinea-pig gastric smooth muscle. Enhancement of slow wave activity is an indirect action of bradykinin through enteric nerve cells embedded in muscle strip.

• The Korean Journal of Physiology
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• 제29권2호
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• pp.203-216
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• 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.

• 대한의생명과학회지
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• 제16권4호
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• pp.259-264
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• 2010

This study was designed to investigate the effects of nitric oxide on the neuronal activity of rat cerebellar Purkinje cells. Sprague-Dawley rats aged 14 to 16 days were decapitated under ether anesthesia. After treatment with pronase and thermolysin, the dissociated Purkinje cells were transferred into a chamber on an inverted microscope. Spontaneous action potentials and potassium current were recorded by standard patch-clamp techniques under current and voltage-clamp modes respectively. 15 Purkinje cells revealed excitatory responses to $20\;{\mu}M$ of sodium nitroprusside (SNP) and 4 neurons (20%) did not respond to SNP. Whole potassium currents of Purkinje cells were decreased by SNP (n=10). Whole potassium currents of Purkinje cells were also decreased by L-arginine, substrate of nitric oxide (n=10). These experimental results suggest that nitric oxide increases the neuronal activity of Purkinje cells by altering the resting membrane potential and after hyperpolarization.

• Journal of Microbiology and Biotechnology
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• 제33권7호
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• pp.857-863
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• 2023

Pathogenic bacteria that colonize the human intestinal tract have evolved strategies to overcome acidic conditions when they pass through the gastrointestinal tract. Amino acid-mediated acid resistance systems are effective survival strategies in a stomach that is full of amino acid substrate. The amino acid antiporter, amino acid decarboxylase, and ClC chloride antiporter are all engaged in these systems, and each one plays a role in protecting against or adapting to the acidic environment. The ClC chloride antiporter, a member of the ClC channel family, eliminates negatively charged intracellular chloride ions to avoid inner membrane hyperpolarization as an electrical shunt of the acid resistance system. In this review, we will discuss the structure and function of the prokaryotic ClC chloride antiporter of amino acid-mediated acid resistance system.

• The Korean Journal of Physiology and Pharmacology
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• 제19권5호
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• pp.435-440
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• 2015

This study aimed to investigate the effect of pituitary adenylate cyclase-activating peptide (PACAP) on the pacemaker activity of interstitial cells of Cajal (ICC) in mouse colon and to identify the underlying mechanisms of PACAP action. Spontaneous pacemaker activity of colonic ICC and the effects of PACAP were studied using electrophysiological recordings. Exogenously applied PACAP induced hyperpolarization of the cell membrane and inhibited pacemaker frequency in a dose-dependent manner (from 0.1 nM to 100 nM). To investigate cyclic AMP (cAMP) involvement in the effects of PACAP on ICC, SQ-22536 (an inhibitor of adenylate cyclase) and cell-permeable 8-bromo-cAMP were used. SQ-22536 decreased the frequency of pacemaker potentials, and cell-permeable 8-bromo-cAMP increased the frequency of pacemaker potentials. The effects of SQ-22536 on pacemaker potential frequency and membrane hyperpolarization were rescued by co-treatment with glibenclamide (an ATP-sensitive $K^+$ channel blocker). However, neither $N^G$-nitro-L-arginine methyl ester (L-NAME, a competitive inhibitor of NO synthase) nor 1H-[1,2,4]oxadiazolo[4,3-${\alpha}$]quinoxalin-1-one (ODQ, an inhibitor of guanylate cyclase) had any effect on PACAP-induced activity. In conclusion, this study describes the effects of PACAP on ICC in the mouse colon. PACAP inhibited the pacemaker activity of ICC by acting through ATP-sensitive $K^+$ channels. These results provide evidence of a physiological role for PACAP in regulating gastrointestinal (GI) motility through the modulation of ICC activity.

• 대한소아치과학회지
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• 제25권4호
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• pp.671-682
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• 1998

Electrophysiological phenomena of pyramidal cells in the CA1 area of the dorsal hippocampus were recorded from and filled with neurobiotin in anesthetized rats. The electropharmacological properties of membrane as well as the cellular-synaptic generation of rhythmic slow activity (theta) were examined. The intracellular response characteristics of these pyramidal cells were distinctly different from responses of interneurons. Pyramidal cells had a high resting membrane potential, a low input resistance, and a large amplitude action potential. A afterhyperpolarization was followed a single action potential. Most of pyramidal cells did not display a spontaneous firing. Pyramidal cells displayed weak inward rectification and anodal break excitation. The slope of the frequency-current relation was 53.4 Hz/nA for the first interspike interval and 15.9 Hz/nA for the last intervals, suggesting the presence of spike frequency adaptation. Neurobiotin-filled neurons showed pyramidal morphology. Cells were generally bipolar dendritc processes ramifying in stratum lacunosum-moleculare, radiatum, and oriens. Commissural stimulation discharged pyramidal cells, followed by excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs). The frequency of theta-related membrane potential oscillation was voltage-independent in pyramidal neurons. At strong depolarization levels (less than 30 mV) pyramidal cells emitted sodium spike oscillation, phase-locked to theta. The observations provide direct evidence that theta-related rhythmic hyperpolarization of principal cells is brought by the rhythmically discharging interneurons. Furthermore, the findings in which interneurons were also paced by rhythmic inhibitory postsynaptic potentials during theta suggest that they were periodically hyperpolarized by their GABAergic septal afferents.

• BMB Reports
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• 제41권6호
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• pp.448-454
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• 2008

Two full-length cDNAs, PutPMP3-1 and PutPMP3-2, encoding PMP3 family proteins were isolated from Puccinellia tenuiflora, a monocotyledonous halophyte. Expression of both genes was induced by low temperature, salt stress, dehydration, ABA, and $NaHCO_3$. Transcripts of PutPMP3-2 were more strongly induced by these stresses relative to those of PutPMP3-1, particularly under low temperature and dehydration conditions. Expression of PutPMP3-1 and PutPMP3-2 in yeast mutants lacking the PMP3 gene can functionally complement the membrane hyper-polarization and salt sensitivity phenotypes resulting from PMP3 deletion. To compare the functions of PutPMP3-1 and PutPMP3-2, the orthologous genes in rice (OsLti6a and OsLti6b) were isolated. Both OsLti6a and OsLti6b could functionally complement the loss of PMP3 in yeast. PutPMP3-2 and OsLti6a were more effective in reversing membrane hyperpolarization than PutPMP3-1 and OsLti6b. However, the four yeast transformants each showed similar levels of salt tolerance. These results imply that these PMP3 family members don't function identically under different stress tolerance conditions.