• The Korean Journal of Physiology and Pharmacology
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• v.7 no.2
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• pp.73-77
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• 2003

The effects of nitric oxide on the vestibular function recovery following unilateral labyrinthectomy (UL) were studied. Sprague-Dawley male rats, treated with nitric oxide liberating agent sodium nitroprusside (SNP) and NOS inhibitor $N^G$-nitro-L-arginine methyl ester (L-NAME), were subjected to destruction of the unilateral vestibular apparatus, and then spontaneous nystagmus was observed in the rat. To explore the effects of nitric oxide on the neuronal excitability, whole cell patch clamp technique was applied on isolated medial vestibular nuclear neurons. The frequency of spontaneous nystagmus in SNP treated rats was lesser than that of spontaneous nystagmus in control animals. In contrast, pre-UL treatment with L-NAME resulted in a significant increase in spontaneous nystagmus frequency. In addition, SNP increased the frequency of spontaneous action potential in isolated medial vestibular nuclear neurons. Potassium currents of the vestibular nuclear neurons were inhibited by SNP. After blockade of calcium dependent potassium currents by high EGTA (11 mM) in a pipette solution, SNP did not inhibit outward potassium currents. 1H-[1,2,4] oxadiazolo [4,3-a] quinozalin-1-one (ODQ), a specific inhibitor of soluble guanylyl cyclase, inhibited the effects of SNP on the spontaneous firing and the potassium current. These results suggest that nitric oxide after unilateral labyrinthectomy would help to facilitate vestibular compensation by inhibiting calcium-dependent potassium currents through increasing intracellular cGMP, and consequently would increase excitability in ipsilateral vestibular nuclear neurons.

• The Korean Journal of Physiology and Pharmacology
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• v.21 no.1
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• pp.75-82
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• 2017

The effects of acepromazine on human ether-$\grave{a}$-go-go-related gene (hERG) potassium channels were investigated using whole-cell voltage-clamp technique in human embryonic kidney (HEK293) cells transfected with hERG. The hERG currents were recorded with or without acepromazine, and the steady-state and peak tail currents were analyzed for the evaluating the drug effects. Acepromazine inhibited the hERG currents in a concentration-dependent manner with an $IC_{50}$ value of $1.5{\mu}M$ and Hill coefficient of 1.1. Acepromazine blocked hERG currents in a voltage-dependent manner between -40 and +10 mV. Before and after application of acepromazine, the half activation potentials of hERG currents changed to hyperpolarizing direction. Acepromazine blocked both the steady-state hERG currents by depolarizing pulse and the peak tail currents by repolarizing pulse; however, the extent of blocking by acepromazine in the repolarizing pulse was more profound than that in the depolarizing pulse, indicating that acepromazine has a high affinity for the open state of the channels, with a relatively lower affinity for the closed state of hERG channels. A fast application of acepromazine during the tail currents inhibited the open state of hERG channels in a concentration-dependent. The steady-state inactivation of hERG currents shifted to the hyperpolarized direction by acepromazine. These results suggest that acepromazine inhibits the hERG channels probably by an open- and inactivated-channel blocking mechanism. Regarding to the fact that the hERG channels are the potential target of drug-induced long QT syndrome, our results suggest that acepromazine can possibly induce a cardiac arrhythmia through the inhibition of hERG channels.

• 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 and Pharmacology
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• v.1 no.3
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• pp.233-240
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• 1997

Neurons in the nucleus raphe magnus are involved in descending modulation of nociceptive transmission. In this study, we attempted to investigate electrophysiological properties of the NRM neurons dissociated from the postnatal rat medulla. The NRM neurons in the coronal slices of and the dissociated neurons from the postnatal rat medullae were immunohistochemically identified using antibody against serotonin. Relatively small number of neurons were positively stained in both preparations. The positively stained neurons displayed large cell body with double or multiple neurites. Using whole-cell patch clamp configuration ionic currents were recorded from the dissociated NRM-like neurons selected by criteria such as size and shape of cell body and cell population. Two types, high- and low-threshold, of voltage-dependent calcium currents were recorded from the dissociated NRM-like neurons. Some neurons displayed both types of calcium currents, whereas others displayed only high-threshold calcium current. Voltage-dependent potassium currents were also recorded from the dissociated NRM neurons. Some neurons displayed both transient outward and delayed rectifier currents but others showed only delayed rectifier current. These results suggest that there are at least two types of calcium currents and two types of potassium currents in the dissociated NRM neurons.

• The Korean Journal of Physiology and Pharmacology
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• v.2 no.2
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• pp.225-232
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• 1998

To investigate the possible involvement of outward potassium ($K^+$) currents in nitric oxide-induced relaxation in intestinal smooth muscle, we used whole-cell patch clamp technique in freshly dispersed guinea-pig ileum longitudinal smooth muscle cells. When cells were held at -60 mV and depolarized from -40 mV to -50 mV in 10 mV increments, sustained outward $K^+$ currents were evoked. The outward $K^+$ currents were markedly increased by the addition of 10 ${\mu}M$ sodium nitroprusside (SNP). 10 ${\mu}M$ S-nitroso-N-acetylpenicillamine (SNAP) and 1 mM 8-Bromo-cyclic GMP (8-Br-cGMP) also showed a similar effect to that of SNP. 1 mM tetraethylammonium (TEA) significantly reduced depolarization-activated outward $K^+$ currents. SNP-enhanced outward $K^+$ currents were blocked by the application of TEA. High EGTA containing pipette solution (10 mM) reduced the control currents and also inhibited the SNP-enhanced outward $K^+$ currents. 5 mM 4-aminopyridine (4-AP) significantly reduced the control currents but showed no effect on SNP-enhanced outward $K^+$ currents. 0.3 ${\mu}M$ apamin and 10 ${\mu}M$ glibenclamide showed no effect on SNP-enhanced outward $K^+$ currents. 10 ${\mu}M$ 1H-[1,2,4]oxadiazolo [4,3-a]quinoxaline-1-one (ODQ), a specific inhibitor of soluble guanylate cyclase, significantly blocked SNP-enhanced $K^+$ currents. We conclude that NO donors activate the $Ca^{2+}-activated$ $K^+$ channels in guinea-pig ileal smooth muscle via activation of guanylate cyclase.

• Biomedical Science Letters
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• v.16 no.1
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• pp.46-52
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• 2010

This study was designed to investigate the effects of sphingosine-1-phosphate on the neuronal activity of rat medial vestibular nuclear neurons. Sprague-Dawley rats aged 14 to 16 days were decapitated under ether anesthesia. After treatment with pronase and thermolysin, the dissociated medial vestibular nuclear neurons were transferred into a chamber on an inverted microscope. Spontaneous action potentials and potassium currents were recorded by standard patch-clamp techniques under current and voltage-clamp modes respectively. 15 medial vestibular nuclear neurons revealed excitatory responses to 1 and $5\;{\mu}M$ of sphingosine-1-phosphate. The spike frequency and resting membrane potential of these cells were increased by sphingosine-1-phosphate. The amplitude of afterhyperpolarization was decreased by sphingosine-1-phosphate. Whole potassium currents of medial vestibular nuclear neurons were decreased by sphingosine-1-phosphate (n=12). Sphingosine-1-phosphate did not affect the charybdotoxin-treated potassium currents. These experimental results suggest that sphingosine-1-phosphate increases the neuronal activity of the medial vestibular nuclear neurons by altering the resting membrane potential and afterhyperpolarization.

• Biomedical Science Letters
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• v.16 no.4
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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.

• The Korean Journal of Physiology and Pharmacology
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• v.17 no.6
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• pp.537-546
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• 2013

Deiters' cells are the supporting cells in organ of Corti and are suggested to play an important role in biochemical and mechanical modulation of outer hair cells. We successfully isolated functionally different $K^+$ currents from Deiters' cells of guinea pig using whole cell patch clamp technique. With high $K^+$ pipette solution, depolarizing step pulses activated strongly outward rectifying currents which were dose-dependently blocked by clofilium, a class III anti-arrhythmic $K^+$ channel blocker. The remaining outward current was transient in time course whereas the clofilium-sensitive outward current showed slow inactivation and delayed rectification. Addition of 5 mM tetraethylammonium (TEA) further blocked the remaining current leaving a very fast inactivating transient outward current. Therefore, at least three different types of $K^+$ current were identified in Deiters' cells, such as fast activating and fast inactivating current, fast activating slow inactivating current, and very fast inactivating transient outward current. Physiological role of them needs to be established.

• The Korean Journal of Physiology and Pharmacology
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• v.27 no.1
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• pp.95-103
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• 2023

Rosiglitazone is a thiazolidinedione-class antidiabetic drug that reduces blood glucose and glycated hemoglobin levels. We here investigated the interaction of rosiglitazone with Kv3.1 expressed in Chinese hamster ovary cells using the wholecell patch-clamp technique. Rosiglitazone rapidly and reversibly inhibited Kv3.1 currents in a concentration-dependent manner (IC₅₀ = 29.8 µM) and accelerated the decay of Kv3.1 currents without modifying the activation kinetics. The rosiglitazonemediated inhibition of Kv3.1 channels increased steeply in a sigmoidal pattern over the voltage range of -20 to +30 mV, whereas it was voltage-independent in the voltage range above +30 mV, where the channels were fully activated. The deactivation of Kv3.1 current, measured along with tail currents, was also slowed by the drug. In addition, the steady-state inactivation curve of Kv3.1 by rosiglitazone shifts to a negative potential without significant change in the slope value. All the results with the use dependence of the rosiglitazone-mediated blockade suggest that rosiglitazone acts on Kv3.1 channels as an open channel blocker.

• International Journal of Precision Engineering and Manufacturing-Green Technology
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• v.5 no.5
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• pp.631-636
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• 2018

Extraction of photosynthetic currents from thylakoids was studied using micro pillar structured electrode. Thylakoids were isolated from spinach leaves, and the size and shape of thylakoids were estimated from scanning electron microscopy images. Based on the geometry information of thylakoids, micro pillar shaped electrode was designed and fabricated using metal-assisted chemical etching of silicon wafers. Influence of photovoltaic effect on the silicon-based micro pillar electrode was confirmed to be negligible. Photosynthetic currents were measured in a three-electrode setup with an electron mediator, potassium ferricyanide. Photosynthetic currents from micro pillar electrodes were enhanced compared with the currents from flat electrodes. This indicates the significance of the enhanced contact between thylakoids and an electrode for harvesting photosynthetic electrons.