• Korean Journal of Veterinary Research
• /
• v.40 no.2
• /
• pp.275-282
• /
• 2000

Substantia nigra is known to highly express glibenclamide binding site, a protein associated to ATP-sensitive $K^{+}$ ($K_{ATP}$) channel in the brain. However, the functional expression of $K_{ATP}$ channels in the area is not yet known. In this work, we attempted to estimate the functional expression of $K_{ATP}$ channels in neurons of the substantia nigra pars compacta (SNC) in young rats using slice patch clamp technique. Membrane properties and whole cell currents attributable to $K_{ATP}$ channel were examined by the current and voltage clamp method, respectively. In SNC, two sub-populations of neurons were identified. Type I (rhythmic) neurons had low frequency rebound action potentials ($4.5{\pm}0.25Hz$, n=75) with rhythmic pattern. Type II (phasic) neurons were characterized by faster firing ($22.7{\pm}3.16Hz$, n=12). Both time constants and membrane capacitance in rhythmic neurons ($34.0{\pm}1.27$ ms, $270.0{\pm}11.83$ pF) and phasic neurons ($23.7{\pm}4.16$ ms, $184{\pm}35.2$ pF) were also significantly different. The current density of $K_{ATP}$ channels was $6.1{\pm}1.47$ pA/pF (2.44~15.43 pA/pF, n=8) at rhythmic neurons of young rats. Our data show that in SNC there are two types of neurons with different electrical properties and the density of $K_{ATP}$, channel of rhythmic neuron is about 600 channels per neuron.

• Progress in Medical Physics
• /
• v.11 no.1
• /
• pp.29-38
• /
• 2000

The signal transduction pathway for most neurotransmitter induced inhibition of $Ca^{2+}$ channels in sympathetic neurons involves a G-protein mediated, membrane-delimited mechanism without the participation of any known protein kinase. However, activation of protein kinase C (PKC) has been proposed as one of the intracellular mechanisms mediating some neurotransmitter induced $Ca^{2+}$ channel inhibition. In the present study, we investigated the effects of phorbol-12, 13-dibutyrate (PDBu) on $Ca^{2+}$ channel currents of acutely dispersed neurons from adult rat superior cervical ganglion (SCG) neurons using whole cell variant of the patch clamp technique. PDBu (500 nM), the activator of PKC, increased $Ca^{2+}$ channel currents and retarded the deactivation of tail currents. The effects of PDBu were voltage dependent and the maximal increase in the current amplitudes was observed between -10 to 10 mV (n=4). PDBu attenuated $Ca^{2+}$ current inhibition induced by norepinephrine (NE), which modulates $Ca^{2+}$ channels via a pertussis toxin (PTX)-sensitive pathway. Inhibition of PDBu by staurosporine (1 $\mu$M) blocked the effects of PDBu on current amplitudes and NE-induced G-protein mediated inhibition of $Ca^{2+}$ currents. Further experiment should be done to know if G-protein or $Ca^{2+}$ channel itself is the target of PKC phosphorvlation.phosphorvlation.

• The Korean Journal of Physiology and Pharmacology
• /
• v.17 no.6
• /
• pp.537-546
• /
• 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
• /
• v.1 no.4
• /
• pp.355-366
• /
• 1997

Although cerebellar Purkinje cells display spontaneous electrical activity in vivo and in slice experiments, the mechanism of the spontaneous activity generation has not been clearly understood. The aim of this study was to investigate whether cerebellar Purkinje cells of postnatal rats generate spontaneous electrical activity without synaptic inputs. Dissociated cerebellar Purkinje cells were used for reducing synaptic inputs in the present study. Cerebellar Purkinje cells with dendrites were dissociated from postnatal rats using enzymatic treatment followed by mechanical trituration. Spontaneous electrical activities were recorded from dissociated cells without any stimulus using whole-cell patch clamp configuration. Two types, spontaneously firing or quiescent, of dissociated Purkinje cells were observed in postnatal rats. Both types of cells were identified as Purkinje cells using immunocytochemical staining technique with anti-calbindin after recording. Spontaneously active cells displayed two patterns of firing, repetitive and burst firings. Two thirds of dissociated Purkinje cells displayed repetitive firing and the rest of them did burst firing under same recording condition. Repetitive firing activities were maintained even after further isolation using either physical or pharmacological techniques. Neither high magnessium solution nor excitatory synaptic blockers, AP-5 and DNQX, block the spontaneous activity. These results demonstrate that spontaneous electrical activity of isolated cerebellar Purkinje cells in postnatal rats is generated by intrinsic membrane properties rather than synaptic inputs.

• The Korean Journal of Physiology and Pharmacology
• /
• v.12 no.1
• /
• pp.25-30
• /
• 2008

Although many studies show that thromboxane $A_2\;(TXA_2)$ has the action of gastrointestinal (GI) motility using GI muscle cells and tissue, there are no reports on the effects of $TXA_2$ on interstitial cells of Cajal (ICC) that function as pacemaker cells in GI tract. So, we studied the modulation of pacemaker activities by $TXA_2$ in ICC with whole cell patch-clamp technique. Externally applied $TXA_2\;(5{\mu}M)$ produced membrane depolarization in current-clamp mode and increased tonic inward pacemaker currents in voltage-clamp mode. The tonic inward currents by $TXA_2$ were inhibited by intracellular application of GDP-${\beta}$-S. The pretreatment of ICC with $Ca^{2+}$ free solution and thapsigargin, a $Ca^{2+}$-ATPase inhibitor in endoplasmic reticulum, abolished the generation of pacemaker currents and suppressed the $TXA_2$-induced tonic inward currents. However, chelerythrine or calphostin C, protein kinase C inhibitors, did not block the $TXA_2$-induced effects on pacemaker currents. These results suggest that $TXA_2$ can regulate intestinal motility through the modulation of ICC pacemaker activities. This modulation of pacemaker activities by $TXA_2$ may occur by the activation of G protein and PKC independent pathway via extra and intracellular $Ca^{2+}$ modulation.

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

• Development and Reproduction
• /
• v.15 no.1
• /
• pp.31-39
• /
• 2011

Change in intracellular $Ca^{2+}$-concentration ($[Ca^{2+}]_i$) is an essential event for egg activation and further development. $Ca^{2+}$ ion is originated from intracellular $Ca^{2+}$-store via inositol 1,4,5-triphosphate receptor and/or $Ca^{2+}$ influx via $Ca^{2+}$ channel. This study was performed to investigate whether changes in $Ca^{2+}$/calmodulin dependent protein kinase II (CaM KII) activity affect $Ca^{2+}$ influx during artificial egg activation with ethanol using $Ca^{2+}$ monitoring system and whole-cell patch clamp technique. Under $Ca^{2+}$ ion-omitted condition, $Ca^{2+}$-oscillation was stopped within 30 min post microinjection of porcine sperm factor, and ethanol-induced $Ca^{2+}$ increase was reduced. To investigate the role of CaM KII known as an integrator of $Ca^{2+}$- oscillation during mammalian egg fertilization, CaM KII activity was tested with a specific inhibitor KN-93. In the eggs treated with KN-93, ethanol failed to induce egg activation. In addition, KN-93 inhibited inward $Ca^{2+}$ current ($I_{Ca}$) in a time-dependent manner in whole-cell configuration. Immunostaining data showed that the voltage-dependent $Ca^{2+}$ channels were distributed along the plasma membrane of mouse egg and 2-cell embryo. From these results, we suggest that $Ca^{2+}$ influx during fertilization might be controlled by CaM KII activity.

• The Korean Journal of Physiology and Pharmacology
• /
• v.7 no.2
• /
• pp.73-77
• /
• 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
• /
• v.28 no.1
• /
• pp.51-59
• /
• 1994

This study was carried out to elucidate the excitatory mechanisms of Substance P in the antral circular muscle, using isometric contraction recording, conventional microelectrode method and whole-cell patch clamp technique. Substance P produced tonic and phasic contractions in a dose-dependent manner and depolarized membrane potential with increased amplitude of slow waves in muscle strips. Voltage-dependent $Ca^{2+}$ currents were increased by the application of Substance P from a holding potential of -60mV to 50mV in 10mV steps and this effect was blocked by the addition of an antagonist. Also Substance P increased transient and spontaneous oscillatory $K^+$ outward currents. The enhanced outward currents were abolished by apamin in dispersed single cells. These results suggest that the depolarization of membrane potential by Substance P activates voltage-dependent $Ca^{2+}$ channels, which represents an excitatory response in the antral circular muscle and led to an increase in $Ca^{2+}\;activated\;K^+\;currents$.

• Biomolecules & Therapeutics
• /
• v.14 no.2
• /
• pp.102-105
• /
• 2006

We examined the effects of psoralen derivatives on a rapidly activating delayed rectifier $K^+$ channel (hKv1.5) cloned from human heart and stably expressed in $Ltk^-$ cells. Using the whole cell configuration of the patch-clamp technique, we found that the five psoralen derivatives inhibited hKv1.5 current. Especially, 4-(2-Propenyloxy)-7H-furo[3,2-g][1]benzopyran-7-one (compound 5) was more potent than the inhibition of the hKv1.5 current of psoralen. The compound 5 inhibited the hKv1.5 current in a concentration-, time-, and voltage-dependent manner. These results suggest that the compound 5 is an excellent candidate as an antiarrhythmic drug for atrial fibrillation.