Cyproheptadine Regulates Pyramidal Neuron Excitability in Mouse Medial Prefrontal Cortex / 神经科学通报·英文版

Cyproheptadine (CPH), a first-generation antihistamine, enhances the delayed rectifier outward K current (I) in mouse cortical neurons through a sigma-1 receptor-mediated protein kinase A pathway. In this study, we aimed to determine the effects of CPH on neuronal excitability in current-clamped pyramidal neurons in mouse medial prefrontal cortex slices. CPH (10 µmol/L) significantly reduced the current density required to generate action potentials (APs) and increased the instantaneous frequency evoked by a depolarizing current. CPH also depolarized the resting membrane potential (RMP), decreased the delay time to elicit an AP, and reduced the spike threshold potential. This effect of CPH was mimicked by a sigma-1 receptor agonist and eliminated by an antagonist. Application of tetraethylammonium (TEA) to block I channels hyperpolarized the RMP and reduced the instantaneous frequency of APs. TEA eliminated the effects of CPH on AP frequency and delay time, but had no effect on spike threshold or RMP. The current-voltage relationship showed that CPH increased the membrane depolarization in response to positive current pulses and hyperpolarization in response to negative current pulses, suggesting that other types of membrane ion channels might also be affected by CPH. These results suggest that CPH increases the excitability of medial prefrontal cortex neurons by regulating TEA-sensitive I channels as well as other TEA-insensitive K channels, probably I and inward-rectifier Kir channels. This effect of CPH may explain its apparent clinical efficacy as an antidepressant and antipsychotic.

Tetraethylammonium-induced Epileptiform Activity and its Modification by GABAA Antagonist in the Rat Visual Cortex

PURPOSE: The goal of this study was to investigate the effect of tetraethylammonium (TEA) on the excitability of visual cortex, and observe the induction of epileptiform activity. Also, it was aimed to define the characteristics of spontaneous activity and observe the effect of GABAA antagonist, NMDA antagonist and non-NMDA antagonist on the TEA-induced epileptiform activity. METHODS: The visual cortex slices in this study were obtained from 19 to 23 day-old Sprague-Dawley rats. Extracellular cellular recording was performed to observe the induction of epileptiform discharge perfused by artificial CSF containing 1, 5 and 10 mM TEA and the effect of 10 ?M 6-cyano-7-nitroquinoxaline-dione disodium(CNQX) and 50 microM D-(-)-2-amino-5-phosphonopentanoic acid(D-AP5) on the 10 mM TEA-induced epileptiform activity. RESULTS: Spontaneous epileptiform activities were observed in 5 and 10 mM TEA groups. The addition of 5 ?M BIC blocked the TEA-induced spontaneous ictal epileptiform activity but didn't block the TEA-induced spontaneous interictal epileptiform activity. The addition of 10 ?M CNQX shortened duration, decreased frequency and amplitude of the TEA-induced spontaneous epileptiform activity. The addition of 50 microM D-AP5 blocked the TEA-induced spontaneous ictal and interictal epileptiform activity. CONCLUSION: TEA induced the increased excitability in the visual cortex and spontaneous epileptiform activity. 5 ?M BIC blocked the TEA-induced spontaneous ictal epileptiform activity and GABAA antagonist BIC plays a role in limiting the epileptiform discharge. The TEA-induced spontaneous epileptiform activity induction was decreased by CNQX and blocked by D-AP5. NMDA and non-NMDA are required to modify the TEA-induced spontaneous epileptiform activity.

Arsenic trioxide-induced HeLa cell death is partially prevented by K + channel blockers / 药学学报

Aim To investigate the effects of K + channel blockers on arsenic trioxide-induced HeLa cell death. Methods Viability of HeLa cells was assessed by mitochondrial dehydrogenase activity using colorimetric MTT assay and the voltage-dependent K+ currents were recorded by using patch-clamp rest living cells after As2 O3 24 h-incubation showed significant increase of K + currents densities. At + 80mV, the densities of K+ currents (61 ± 18) pA/10 pF (n = 8) in As2O3 24 h-incubation group were significantly more than that in the control group (38 ± 10) pA/10 pF (n = 8, P ＜ 0. 05 ). The HeLa cells were prevented partially from As2 O3-induced cell death by co-application for 24 h with typical voltageeffects on HeLa cells. Conclusion Chronic treatment with As2 O3 increased voltage-dependent K+currents in HeLa cells and the cell death induced by As2O3 was reduced partially by voltage-dependent K +channel blockers, 4-aminopyridine or tetraethylammonium.

Inhibitory Effects of Potassium Channel Blockers on Carbachol-induced Contraction in Rat Detrusor Muscle

We present accidental findings that potassium channel blockers, such as tetraethyl-ammonium (TEA) or 4-aminopyridine (4-AP), inhibit the sustained tonic contraction induced by carbachol in rat detrusor muscle strips. The relatively lower concentrations (5 mM) potentiated phasic contractions. The potentiation of phasic contraction was not observed in nicardipine pretreated condition. In nicardipine pretreated condition, the concentration-response curves for the negative inotropic effect of potassium channel blockers were shifted to the right by the increasing concentration of carbachol from 0.5 micrometer to 5 micrometer. IC50 was changed significantly from 0.19 to 0.64 mM (TEA) and from 0.21 to 0.96 (4-AP). Such inhibitory effects were also observed in Ca2+ depleted condition, where 0.1 mM EGTA and 1 micrometer thapsigargin were added into Ca2+ free solution. In conclusion, inhibitory effects of potasssium channel blockers on carbachol-induced contraction may be ascribed to the direct inhibition of receptor-agonist binding.

Effect of potassium channel blocker tetraethylammonium on proliferation and apoptosis of ovarian cancer cell / 解放军医学杂志

Objective To study the effects of potassium channel blocker,tetraethylammonium(TEA) on the proliferation and apoptosis of ovarian cancer cell line SKOV3.Methods SKOV3 cells were treated with TEA.The effect of TEA on proliferation of SKOV3 cells was assessed by MTT assay.Hoechst 33258 fluorescein staining and flow cytometry(FCM) were employed in detection of SKOV3 cells apoptosis.Results TEA(1,5,10 and 20mmol/L) can significantly inhibit the proliferation of SKOV3 cells,the inhibitory rates were 8.61%,18.86%,46.63% and 65.22%,respectively(P

Effect of K+-channel blockers on the muscarinic- and A|1-adenosine-receptor coupled regulation of electrically evoked acetylcholine release in the rat hippocampus

It was attempted to clarify the participation of K+ channels in the post-receptor mechanisms of the muscarinic and A1-adenosine receptor-mediated control of acetylcholine (ACh) release in the present study. Slices from the rat hippocampus were equilibrated with (3H)choline and the release of the labelled products was evoked by electrical stimulation (3 Hz, 5 V/cm, 2 ms, rectangular pulses), and the influence of various agents on the evoked tritium-outflow was investigated. Oxotremorine (Oxo, 0.1~10 micrometer), a muscarinic agonist, and N6-cyclopentyladenosine (CPA, 1~30 micrometer), a specific A1-adenosine agonist, decreased the ACh release in a dose-dependent manner, without affecting the basal rate of release. 4-aminopyridine (4AP), a specific A-type K+-channel blocker (1~100 micrometer), increased the evoked ACh release in a dose-related fashion, and the basal rate of release is increased by 3 and 100 micrometer. Tetraethylammonium (TEA), a non-specific K+-channel blocker (0.1~10 mM), increased the evoked ACh release in a dose-dependent manner without affecting the basal release. The effects of Oxo and CPA were not affected by 3 micrometer 4AP co-treatment, but 10 mM TEA significantly inhibited the effects of Oxo and CPA. 4AP (10 micrometer- and TEA (10 mM)-induced increments of evoked ACh release were completely abolished in Ca2+-free medium, but these were recovered in low Ca2+ medium. And the effects of K+-channel blockers in low Ca2+ medium were inhibited by Mg2+ (4 mM) and abolished by 0.3 micrometer tetrodotoxin (TTX). These results suggest that the changes in TEA-sensitive potassium channel permeability and the consequent limitation of Ca2+ influx are partly involved in the presynaptic modulation of the evoked ACh-release by muscarinic and A1-adenosine receptors of the rat hippocampus.

Effects of K+ channel modulators on extracellular K+ accumulation during ischemia in the rat hippocampal slice

Loss of synaptic transmission and accumulation of extracellular K+((K+)o) are the key features in ischemic brain damage. Here, we examined the effects of several K+ channel modulators on the early ischemic changes in population spike (PS) and (K+)o in the CA1 pyramidal layer of the rat hippocampal slice using electrophysiological techniques. After onset of anoxic aglycemia (AA), orthodromic field potentials decreased and disappeared in 3.3 +/- 0.22 min (mean +/- SEM, n = 40). The hypoxic injury potential (HIP), a transient recovery of PS appeared at 6.0 +/- 0.25 min (n = 40) in most slices during AA and lasted for 3.3 +/- 0.43 min. (K+)o increased initially at a rate of 0.43 mM/min (Phase 1) and later at a much faster rate (12.45 mM/min, Phase 2). The beginning of Phase 2 was invariably coincided with the disappearance of HIP. Among K+ channel modulators tested such as 4-aminopyridine (0.03, 0.3 mM), tetraethylammonium (0.1 mM), NS1619 (0.3 ~ 10 muM), niflumic acid (0.1 mM), glibenclamide (40 muM), tolbutamide (300 muM) and pinacidil (100 muM), only 4-aminopyridine (0.3 mM) induced slight increase of (K+)o during Phase 1. However, none of the above agents modulated the pattern of Phase 2 in (K+)o in response to AA. Taken together, the experimental data suggest that 4-aminopyridine-sensitive K+ channels, large conductance Ca2+/-activated K+ channels and ATP-sensitive K+ channels may not be the major contributors to the sudden increase of (K+)o during the early stage of brain ischemia, suggesting the presence of other routes of K+ efflux during brain ischemia.

Effect of Tetraethylammonium on the Contractile Reponse in the Isolated Rat Phrenic: Hemidiaphra / 대한마취과학회지

BACKGROUND: Recently, the phannacologic and therapeutic significance of various types of potassium channels are being realized. Thus it was attempted to delineate the role of voltage-gated K+ -channels on the excitation-contraction coupling in skeletal muscle. METHODS: The effects of tetraethylammonium, a well known K+ -channel blocker, on the electrically-evoked twitch response, train-of-four and tetanic stimulation, and the influence of various agents on the these effects were studied in the isolated rat hemi-diaphragm preparation. RESULTS: Tetraethylammonium (1 & 3 mM) increased the electrically-evoked twitch response, but the large dose (10 mM) decreased the twitch response. And tetraethylammonium decreased the TOF- and tetanus-ratio in a dose-related fashion. d-Tubocurarine(1 microM) decreased the twitch response, and tetraethylammonium recovered the d-tubocurarine-induced-depression of twitch response. When the Ca++(6x) and K+ (2x) concentration of the medium were increased, the twitch response caused by tetraethylammonium were slightly inhibited than that observed in the normal solution, but the fade phenomenon was potentiated. The tetraethylammonium (10 mM)-induced depression of twitch response were reduced by reducing the stimulus frequency to 0.01 Hz and choline (400 microM) treatment. And N-ethylmaleimide inhibited the tetraethylammonium-induced increment of twitch response and also potentiated the tetraethylammonium-induced fade phenomenon. However, it is noteworth the 4-aminopy- ridine, another K+ -channel bloker, potentiated the electrically-evoked twitch response but did not affect the TOF-and tetanusratio. CONCLUSION: These result indicate that tetraethylammonium elicited two districtive types of response in the rat phrenic-hemidiaphragm preparation. The potentiating effects of twitch response is mediated by blocking delayed K+ -rectifier channel and decreasing effects of twitch response, TOF-and tetanus-ratio is may be due to decreased the acetylcholine release from presynaptic nerve terminal.

Effect of K+ channel Blocker on Vasodilation by Halothane / 대한마취과학회지

Halothane is a popular inhalation anesthetics in practice, which has been reported to cause a vasodilation through a direct depressant action on vascular smooth muscle, or by an indirect attenuation of vasoconstrictor activity. The membrane potential of the vascular smooth muscle cell is mainly regulated by the flow of Ca2+ and K+ ions through specialized channels. The purpose of this study was to determine whether blockade of the K+ channel alter the response to halothane vasodilating action. This study was done with rat thoracic aorta in tissue bath. Isometric tension of the ring (3~4 mm in length) was recorded. In halothane alone group (n=15), after precontraction with norepinephrine (10(-7) M), ring was exposed with halothane 0.7%, 1.5%, 2.1% concentration for 15 minutes, sequentially. The procedure of calcium activated K+ channel blocker pretreated group (n=12) was same manner as halothane alone group after tetraethylammonium (TEA 20 mM) pretreatment. The result of this study was shown to followings; 1) Vasodilation correlate with halothane concentration (p<0.05). 2) Vasodilation in tetraethylammonium (TEA) pretreated group also augmented 'significantly (p<0.05). 3) Especially, in the halothane 1.5%, 2.1%, the presence of TEA significantly potentiate vasodilating effect: halothane alone group, -35%, -53%: TEA group, -47%, -71%(p<0.05). These result demonstrate that: 1) halothane induce relaxation of rat aorta. 2) K+ charinel blokade potentiate the vasodilating effect of halothane.

The Effect of Tetraethylammonium Chloride on the Impulse Conduction Block by bupivacaine / 대한마취과학회지

Potassium channel blockers slow depolarization, broaden the action potential, and thus pro- mote the open and inactivated Na+ channel states. The ability of local anesthetics to reduce the amplitude of compound action potential(CAP) of rat sciatic nerve was examined in the presence and absence of teteraethylammonium chloride(TEA) that selectively block K+ channels, In the presence of 1.3X10-5 M bupivacaine that inhibit the CAP by 22.5% at tonic stimulation, the addition of TEA(10-1M) increased this inhibition by another 27.5% and increased another 50% by phasic stimulation(20Hz). Also, dose response curve of bupivacaine in the presence of TEA(10-1M) showed marked shift to left of curve. The re- covery kinetics of bupivacaine in the presence of various coneentration of TEA(10-2-10-1M) showed marked delay of recovery(2X10-2 M), reocurrence of inhibition(90min,5X10-2 M), even no recovery(10-1M). TEA alone slightly depolarized the resting membrane which was represented as increment of CAP height from 0.9%(3min) to 12.3%(80min), and broadened mid-peak amplitude width by 2 times in 5X10-1M, 5.3 times in 1M. These experiments directly demonstrated that TEA potentiated the inhibition of CAP by bupivacaine and showed the poesibility of mixture of TEA and local anesthetics to potenti- ate impulse conduction blockade.