• The Korean Journal of Physiology and Pharmacology
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• v.1 no.5
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• pp.555-563
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• 1997

The effects of pH on $K^+$ currents were investigated in single smooth muscle cells isolated from the thoracic aorta of Wistar-Kyoto rats. Whole-cell $K^+$ currents were recorded in the conventional configuration of the voltage-clamp technique. Pinacidil (10uM) activated the whole-cell current and the pinacidil-activated current was completely inhibited by glibenclamide (10uM) , an inhibitor of ATP-sensitive $K^+$ channel ($K_{ATP}$ channel). Pinacidil-activated current was reversed at near the $K^+$ equilibrium potential. This current was time- and voltage-independent and reduced by elevating intracellular ATP. Pinacidil-activated current was reduced by lowering the external pH. However, alteration of internal pH has controversial effects on pinacidil-activated current. When the single cell was dialyzed with 0.1 mM ATP, alteration of internal pH had no effect on pinacidil-activated $K^+$ current. In the contrast, when the single cell was dialyzed with 3 mM ATP, pinacidil-activated current was increased by lowering internal pH. Our results suggest that $K^+$ channel activated by pinacidil may be $K_{ATP}$ channel and internal $H^+$ may reduce the inhibitory effect of ATP on $K_{ATP}$ channel.

• The Korean Journal of Physiology and Pharmacology
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• v.1 no.6
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• pp.613-624
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• 1997

Dorsal root ganglion (DRG) is composed of neuronal cell bodies of primary afferents with diverse functions. Various types of ion channels present on DRG neurons may reflect those functions. In the present study, voltage-gated potassium currents in DRG neurons of neonatal rats were characterized by whole-cell voltage clamp method. Two types of delayed rectifier and three types of transient potassium currents were identified according to their electrophysiological properties. The delayed rectifier currents were named $I_{Ke}$ (early inactivating) and $I_{K1}$ (late inactivating). Steady state inactivation of $I_{Ke}$ began from -100 mV lasting until -20 mV. $I_{K1}$ could be distinguished from $I_{Ke}$ by its inactivation voltage range, from -70 mV to +10 mV. Three transient currents were named $I_{Af}$ (fast inactivation), $I_{Ai}$ (intermediate inactivation kinetics), and $I_{As}$ (slow inactivation). $I_{Af}$ showed fast inactivation with time constant of $10.6{\pm}2.0$ msec, $I_{Ai}$ of $36.9{\pm}13.9$ msec, and $I_{As}$ of $60.6{\pm}2.9$ msec at +30 mV, respectively. They also had distinct steady state inactivation range of each. Each cell expressed diverse combination of potassium currents. The cells most frequently observed were those which expressed both $I_{K1}$ and $I_{Af}$, and they had large diameters. The cells expressing $I_{Ke}$ and expressing $I_{Ke}$, $I_{Ai}$, and $I_{As}$ usually had small diameters. Judging from cell diameter, capsaicin sensitivity or action potential duration, candidates for nociceptor were the cells expressing $I_{Ke}$, expressing $I_{Ke}$ and $I_{Ai}$, and expressing $I_{Ke}$ and $I_{As}$. The types and distribution of potassium currents in neonatal rat DRG were similar to those of adult rat DRG (Gold et al, 1996b).

• The Korean Journal of Physiology
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• v.27 no.2
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• pp.175-183
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• 1993

There are many report suggesting that influx and intracellular calcium concentration $([Ca^{2+}]_i)$ are related to cell signalling in various cells. However, it has not been reported that calcium channel activation is affected by the substances involved in signal transduction pathways in the mouse eggs. In this study, the effects of isoprenaline (ISP) and cyclic AMP on calcium influx through calcium channels were investigated to show their relationship with the signal transduction process in unfertilized mouse eggs. Using whole cell voltage clamp techniques, calcium currents, elicited by the depolarizing pulses of 300 ms duration (from -50 mV to 50 mV in 10 mV increments) from a holding potential of -80 mV, were recorded. The current-voltage (I-V) relation of calcium currents was shown to be bell-shaped; the current began to activate at -50 mV and reached its maximum $(-1.33{\pm}0.16\;nA:\;mean{\pm}S.E.,\;n=7)$ at -10 mV, then decayed at around 50 mV. Calcium currents were fully activated within $7\;ms{\sim}20\;ms$ and completely inactivated 200 ms after onset of the step pulse. ISP within the concentration ranges of $10^{-8}\;M{\sim}10^{-4}\;M$ dose-dependently increased the amplitude calcium current. The permeable cyclic AMP analogue,8-bromocyclic AMP, also increased its maximal amplitude by 46ft at $10^{-5}\;M$, while protein kinase inhibitor (PKI), which is known to inhibit 0.02 phosphorylating units of cyclic AMP-dependent protein kinase (PKA) per microgram decreased calcium currents. Currents recorded in the presence of PKI were resistant to increase by the application of $10^{-5}\;M$. Also, PKI inhibited the calcium current increase elicited by ISP treatment. These results suggest that $\beta-adrenergic$ regulation of the calcium channel is mediated by the cAMP-dependent protein kinase. This signal transduction pathway might play a role in regulating $[Ca^{2+}]_i$, level due to the increase of calcium influx in mouse eggs.

• The Korean Journal of Physiology and Pharmacology
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• v.5 no.5
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• pp.373-380
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• 2001

The action of opioid on the hyperpolarization-activated cation current $(I_h)$ in substantia gelatinosa neurons were investigated by using whole-cell voltage-clamp recording in rat spinal brain slices. Hyperpolarizing voltage steps revealed slowly activating currents in a subgroup of neurons. The half-maximal activation and the reversal potential of the current were compatible to neuronal $I_h.$ DAMGO $(1\;{\mu}M),$ a selective- opioid agonist, reduced the amplitude of $I_h$ reversibly. This reduction was dose-dependent and was blocked by CTOP $(2\;{\mu}M),$ a selective ${\mu}-opioid$ antagonist. DAMGO shifted the voltage dependence of activation to more hyperpolarized potential. Cesium (1 mM) or ZD 7288 $(100\;{\mu}M)$ blocked $I_h$ and the currents inhibited by cesium, ZD 7288 and DAMGO shared a similar time and voltage dependence. These results suggest that activation of ${\mu}-opioid$ receptor by DAMGO can inhibit $I_h$ in a subgroup of rat substantia gelatinosa neurons.

• Clinical and Experimental Pediatrics
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• v.53 no.9
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• pp.845-851
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• 2010

Purpose: Recombinant human growth hormone (rhGH) has been widely used to treat short stature. However, there are some concerns that growth hormone treatment may induce skeletal maturation and early onset of puberty. In this study, we investigated whether rhGH can directly affect the neuronal activities of of gonadotropin-releasing hormone (GnRH). Methods: We performed brain slice gramicidin-perforated current clamp recording to examine the direct membrane effects of rhGH on GnRH neurons, and a whole-cell voltage-clamp recording to examine the effects of rhGH on spontaneous postsynaptic events and holding currents in immature (postnatal days 13-21) and adult (postnatal days 42-73) mice. Results: In immature mice, all 5 GnRH neurons recorded in gramicidin-perforated current clamp mode showed no membrane potential changes on application of rhGH (0.4, $1{\mu}g/mL$). In adult GnRH neurons, 7 (78%) of 9 neurons tested showed no response to rhGH ($0.2-1{\mu}g/mL$) and 2 neurons showed slight depolarization. In 9 (90%) of 10 immature neurons tested, rhGH did not induce any membrane holding current changes or spontaneous postsynaptic currents (sPSCs). There was no change in sPSCs and holding current in 4 of 5 adult GnRH neurons. Conclusion: These findings demonstrate that rhGH does not directly affect the GnRH neuronal activities in our experimental model.

• The Korean Journal of Physiology and Pharmacology
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• v.20 no.1
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• pp.75-82
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• 2016

Paroxetine, a selective serotonin reuptake inhibitor (SSRI), has been reported to have an effect on several ion channels including human ether-a-go-go-related gene in a SSRI-independent manner. These results suggest that paroxetine may cause side effects on cardiac system. In this study, we investigated the effect of paroxetine on Kv1.5, which is one of cardiac ion channels. The action of paroxetine on the cloned neuronal rat Kv1.5 channels stably expressed in Chinese hamster ovary cells was investigated using the whole-cell patch-clamp technique. Paroxetine reduced Kv1.5 whole-cell currents in a reversible concentration-dependent manner, with an $IC_{50}$ value and a Hill coefficient of $4.11{\mu}M$ and 0.98, respectively. Paroxetine accelerated the decay rate of inactivation of Kv1.5 currents without modifying the kinetics of current activation. The inhibition increased steeply between -30 and 0 mV, which corresponded with the voltage range for channel opening. In the voltage range positive to 0 mV, inhibition displayed a weak voltage dependence, consistent with an electrical distance ${\delta}$ of 0.32. The binding ($k_{+1}$) and unbinding ($k_{-1}$) rate constants for paroxetine-induced block of Kv1.5 were $4.9{\mu}M^{-1}s^{-1}$ and $16.1s^{-1}$, respectively. The theoretical $K_D$ value derived by $k_{-1}/k_{+1}$ yielded $3.3{\mu}M$. Paroxetine slowed the deactivation time course, resulting in a tail crossover phenomenon when the tail currents, recorded in the presence and absence of paroxetine, were superimposed. Inhibition of Kv1.5 by paroxetine was use-dependent. The present results suggest that paroxetine acts on Kv1.5 currents as an open-channel blocker.

• The Korean Journal of Physiology
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• v.28 no.2
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• pp.143-150
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• 1994

The whole-cell mode of the patch clamp technique was used to study $Ca^{2+}-activated\;Cl^-\;current$ $(I_{Cl_{Ca}})$ in gastric antral myocytes. Extracellular application of caffeine evoked $Ca^{2+}-activated\;current$. In order to isolate the chloride current from background current, all known systems were blocked with specific blockers. The current-voltage relationship of caffeine-induced current showed outward rectification and it reversed at around $E_{Cl^-}$. The shift of reversal potential upon the alteration of external and internal chloride concentrations was well fitted with results which were calculated by the Nernst equation. Extracellular addition of N-phenylanthranilic acid and niflumic acid which are known anion channel blockers abolished the caffeine induced current. Intracellular application of a high concentration of EGTA also abolished this current. Application of c-AMP, c-GMP, heparin, or $AIF^-_4$ made no remarkable changes to this current. Sodium replacement with the impermeable cation N-methylglucamine or with $Cd^{2+}$ rarely affected this current. From the above results it is suggested that the caffeine induced current was a $Cl^-$ current and it was activated by intracellular $Ca^{2+}$.

• The Korean Journal of Physiology and Pharmacology
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• v.11 no.3
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• pp.79-84
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• 2007

Because synaptic refinement of medial nucleus of trapezoid body (MNTB) - lateral superior olive (LSO) synapses is most active during the first postnatal week and the long term depression (LTD) has been suggested as one of its mechanisms, LTD of MNTB-LSO synapses was investigated in neonatal rat brain stem slices with the whole cell voltage clamp technique. In $Mg^{2+}$ free condition, tetanus (10 stimuli at 10 Hz for 2 min) in the current clamp mode induced a robust LTD of isolated D, L-APV-sensitive postsynaptic currents (PSCs) for more than 30 min ($n=6,\;2.4{\pm}0.4%$ of the control), while isolated CNQX-sensitive PSCs were not suppressed ($n=6,\;95.3{\pm}1.6%$). Tetanus also elicited similar LTD in the isolated GABAergic/glycinergic PSCs ($n=6,\;3.6{\pm}0.5%$) and mixed PSCs (GABAergic/glycinergic/glutamatergic) ($n=4,\;2.2{\pm}0.7%$). However, such a strong LTD was not observed in the mixed PSCs when 10 mM EGTA was added in the internal solution (n=10), indicating that postsynaptic $Ca^{2+}$ rise is needed for the strong LTD. This robust LTD might contribute to the active synaptic refinement occurring during the first postnatal week.

• The Korean Journal of Physiology and Pharmacology
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• v.10 no.2
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• pp.59-64
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• 2006

The effects of $Zn^{2+}$ on spontaneous glutamate and GABA release were tested in mechanically dissociated rat CA3 pyramidal neurons which retained functional presynaptic nerve terminals. The spontaneous miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs, respectively) were pharmacologically isolated and recorded using whole-cell patch clamp technique under voltage-clamp conditions. $Zn^{2+}$ at a lower concentration $(30{\mu}M)$ increased GABAergic mIPSC frequency without affecting mIPSC amplitude, but it decreased both mIPSC frequency and amplitude at higher concentrations $({\ge}300{\mu}M)$. In contrast, $Zn^{2+}$ (3 to $100{\mu}M$) did not affect glutamatergic mEPSCs, although it slightly decreased both mIPSC frequency and amplitude at $300{\mu}M$ concentration. Facilitatory effect of $Zn^{2+}$ on GABAergic mIPSC frequency was occluded either in $Ca^{2+}$-free external solution or in the presence of $100{\mu}M$ 4-aminopyridine, a non-selective $K^{+}$ channel blocker. The results suggest that $Zn^{2+}$ at lower concentrations depolarizes GABAergic nerve terminals by blocking $K^{+}$ channels and increases the probability of spontaneous GABA release. This $Zn^{2+}$-mediated modulation of spontaneous GABAergic transmission is likely to play an important role in the regulation of neuronal excitability within the hippocampal CA3 area.

• The Korean Journal of Physiology and Pharmacology
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• v.4 no.1
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• pp.9-14
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• 2000

$K^+$ currents play multiple roles in the excitability of dorsal root ganglion (DRG) neurons. Influences on these currents change the shape of the action potential, its firing threshold and the resting membrane potential. In this study, whole cell configuration of patch clamp technique had been applied to record the blocking effect of capsaicin, a lipophilic alkaloid, on the delayed rectifier $K^+$ current in cultured small diameter DRG neurons of adult rat. Capsaicin reduced the amplitude of $K^+$ current in dose dependent manner, and the concentration-dependence curve was well described by the Hill equation with $K_D$ value of $19.1{\mu}M.$ The blocking effect of capsaicin was reversible. Capsaicin $(10 {\mu}M)$ shifted the steady-state inactivation curve in the hyperpolarizing direction by about 15 mV and increased the rate of inactivation. The voltage dependence of activation was not affected by capsaicin. These multiple effects of capsaicin may suggest that capsaicin bind to the region of $K^+$ channel, participating in inactivation process.