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.

Taurine relaxes human radial artery through potassium channel opening action

The vascular actions and mechanisms of taurine were investigated in the isolated human radial artery (RA). RA rings were suspended in isolated organ baths and tension was recorded isometrically. First, a precontraction was achieved by adding potassium chloride (KCl, 45 mM) or serotonin (5-hydroxytryptamine, 5-HT, 30 µM) to organ baths. When the precontractions were stable, taurine (20, 40, 80 mM) was added cumulatively. Antagonistic effect of taurine on calcium chloride (10 µM to 10 mM)-induced contractions was investigated. Taurine-induced relaxations were also tested in the presence of the K⁺ channel inhibitors tetraethylammonium (1 mM), glibenclamide (10 µM) and 4-aminopyridine (1 mM). Taurine did not affect the basal tone but inhibited the contraction induced by 5-HT and KCl. Calcium chloride-induced contractions were significantly inhibited in the presence of taurine (20, 40, 80 mM) (p<0.05). The relaxation to taurine was inhibited by tetraethylammonium (p<0.05). However, glibenclamide and 4-aminopyridine did not affect taurine-induced relaxations. Present experiments show that taurine inhibits 5-HT and KCl-induced contractions in RA, and suggest that large conductance Ca²⁺-activated K⁺ channels may be involved in taurine-induced relaxation of RA.

Elucidation of the profound antagonism of contractile action of phenylephrine in rat aorta effected by an atypical sympathomimetic decongestant

Vasoconstrictive properties of sympathomimetic drugs are the basis of their widespread use as decongestants and possible source of adverse responses. Insufficiently substantiated practice of combining decongestants in some marketed preparations, such are those containing phenylephrine and lerimazoline, may affect the overall contractile activity, and thus their therapeutic utility. This study aimed to examine the interaction between lerimazoline and phenylephrine in isolated rat aortic rings, and also to assess the substrate of the obtained lerimazoline-induced attenuation of phenylephrine contraction. Namely, while lower concentrations of lerimazoline (10⁻⁶ M and especially 10⁻⁷ M) expectedly tended to potentiate the phenylephrine-induced contractions, lerimazoline in higher concentrations (10⁻⁴ M and above) unexpectedly and profoundly depleted the phenylephrine concentration-response curve. Suppression of NO with NO synthase (NOS) inhibitor N(w)-nitro-L-arginine methyl ester (L-NAME; 10⁻⁴ M) or NO scavanger OHB₁₂ (10⁻³ M), as well as non-specific inhibition of K⁺-channels with tetraethylammonium (TEA; 10⁻³ M), have reversed lerimazoline-induced relaxation of phenylephrine contractions, while cyclooxygenase inhibitor indomethacin (10⁻⁵ M) did not affect the interaction between two vasoconstrictors. At the receptor level, non-selective 5-HT receptor antagonist methiothepin reversed the attenuating effect of lerimazoline on phenylephrine contraction when applied at 3×10⁻⁷ and 10⁻⁶ M, but not at the highest concentration (10⁻⁴ M). Neither the 5-HT1D-receptor selective antagonist BRL 15572 (10⁻⁶ M) nor 5-HT₇ receptor selective antagonist SB 269970 (10⁻⁶ M) affected the lerimazoline-induced attenuation of phenylephrine activity. The mechanism of lerimazoline-induced suppression of phenylephrine contractions may involve potentiation of activity of NO and K⁺-channels and activation of some methiothepin-sensitive receptors, possibly of the 5-HT(2B) subtype.

ß-Citronellol, an alcoholic monoterpene with inhibitory properties on the contractility of rat trachea

β-Citronellol is an alcoholic monoterpene found in essential oils such Cymbopogon citratus (a plant with antihypertensive properties). β-Citronellol can act against pathogenic microorganisms that affect airways and, in virtue of the popular use of β-citronellol-enriched essential oils in aromatherapy, we assessed its pharmacologic effects on the contractility of rat trachea. Contractions of isolated tracheal rings were recorded isometrically through a force transducer connected to a data-acquisition device. β-Citronellol relaxed sustained contractions induced by acetylcholine or high extracellular potassium, but half-maximal inhibitory concentrations (IC50) for K+-elicited stimuli were smaller than those for cholinergic contractions. It also inhibited contractions induced by electrical field stimulation or sodium orthovanadate with pharmacologic potency equivalent to that seen against acetylcholine-induced contractions. When contractions were evoked by selective recruitment of Ca2+ from the extracellular medium, β-citronellol preferentially inhibited contractions that involved voltage-operated (but not receptor-operated) pathways. β-Citronellol (but not verapamil) inhibited contractions induced by restoration of external Ca2+ levels after depleting internal Ca2+ stores with the concomitant presence of thapsigargin and recurrent challenge with acetylcholine. Treatment of tracheal rings with L-NAME, indomethacin or tetraethylammonium did not change the relaxing effects of β-citronellol. Inhibition of transient receptor potential vanilloid subtype 1 (TRPV1) or transient receptor potential ankyrin 1 (TRPA1) receptors with selective antagonists caused no change in the effects of β-citronellol. In conclusion, β-citronellol exerted inhibitory effects on rat tracheal rings, with predominant effects on contractions that recruit Ca2+ inflow towards the cytosol by voltage-gated pathways, whereas it appears less active against contractions elicited by receptor-operated Ca2+ channels.

Mechanisms involved in the vasorelaxant effects produced by the acute application of amfepramone in vitro to rat aortic rings

Amfepramone (diethylpropion) is an appetite-suppressant drug used for the treatment of overweight and obesity. It has been suggested that the systemic and central activity of amfepramone produces cardiovascular effects such as transient ischemic attacks and primary pulmonary hypertension. However, it is not known whether amfepramone produces immediate vascular effects when applied in vitro to rat aortic rings and, if so, what mechanisms may be involved. We analyzed the effect of amfepramone on phenylephrine-precontracted rat aortic rings with or without endothelium and the influence of inhibitors or blockers on this effect. Amfepramone produced a concentration-dependent vasorelaxation in phenylephrine-precontracted rat aortic rings that was not affected by the vehicle, atropine, 4-AP, glibenclamide, indomethacin, clotrimazole, or cycloheximide. The vasorelaxant effect of amfepramone was significantly attenuated by NG-nitro-L-arginine methyl ester (L-NAME) and tetraethylammonium (TEA), and was blocked by removal of the vascular endothelium. These results suggest that amfepramone had a direct vasorelaxant effect on phenylephrine-precontracted rat aortic rings, and that inhibition of endothelial nitric oxide synthase and the opening of Ca2+-activated K+ channels were involved in this effect.

Suplementação mineral e vitamínica em doenças crônicas e de convalescença / Mineral and vitamin supplementation in chronic diseases and convalescence

A síndrome de fadiga crônica (SFC) é uma condição clínica que, apesar de muito prevalente, tem tratamento controverso. A suplementação com substratos como glutamina e vitaminas pode atuar como adjuvante terapêutico. Os autores descrevem um medicamento que pode atender essa finalidade, composto por glutamina 200mg, glutamato de cálcio 250mg, cloridrato de piridoxina 20mg e fosfato de ditetraetilamônio 6mg. São descritas também as ações de cada um dos componentes, e como podem auxiliar na terapêutica da SFC e em períodos de convalescença em diversas condições.

The chronic fatigue syndrome (CFS) is a clinical condition which, although highly prevalent, treatment is controversial and supplementation of substrates such as glutamine and vitamins can act as therapeutic adjuvant. A drug composition that can serve this purpose, the composition is glutamine 200mg, 250mg calcium glutamate, 20mg pyridoxine hydrochloride and phosphate ditetraetilammonium 6mg is described. Also described the actions of each component and how they can assist in the treatment of CFS and in periods of convalescence from various other conditions described.

H2 Receptor-Mediated Relaxation of Circular Smooth Muscle in Human Gastric Corpus: the Role of Nitric Oxide (NO)

This study was designed to examine the effects of histamine on gastric motility and its specific receptor in the circular smooth muscle of the human gastric corpus. Histamine mainly produced tonic relaxation in a concentration-dependent and reversible manner, although histamine enhanced contractility in a minor portion of tissues tested. Histamine-induced tonic relaxation was nerve-insensitive because pretreatment with nerve blockers cocktail (NBC) did not inhibit relaxation. Additionally, K+ channel blockers, such as tetraethylammonium (TEA), apamin (APA), and glibenclamide (Glib), had no effect. However, N(G)-nitro-L-arginine methyl ester (L-NAME) and 1H-(1,2,4)oxadiazolo (4,3-A) quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase (sGC), did inhibit histamine-induced tonic relaxation. In particular, histamine-induced tonic relaxation was converted to tonic contraction by pretreatment with L-NAME. Ranitidine, the H2 receptor blocker, inhibited histamine-induced tonic relaxation. These findings suggest that histamine produced relaxation in circular smooth muscle of human gastric smooth muscle through H2 receptor and NO/sGC pathways.

Effects of Lubiprostone on Pacemaker Activity of Interstitial Cells of Cajal from the Mouse Colon

Lubiprostone is a chloride (Cl-) channel activator derived from prostaglandin E1 and used for managing constipation. In addition, lubiprostone affects the activity of gastrointestinal smooth muscles. Interstitial cells of Cajal (ICCs) are pacemaker cells that generate slow-wave activity in smooth muscles. We studied the effects of lubiprostone on the pacemaker potentials of colonic ICCs. We used the whole-cell patch-clamp technique to determine the pacemaker activity in cultured colonic ICCs obtained from mice. Lubiprostone hyperpolarized the membrane and inhibited the generation of pacemaker potentials. Prostanoid EP1, EP2, EP3, and EP4 antagonists (SC-19220, PF-04418948, 6-methoxypyridine-2-boronc acid N-phenyldiethanolamine ester, and GW627368, respectively) did not block the response to lubiprostone. L-NG-nitroarginine methyl ester (L-NAME, an inhibitor of nitric oxide synthase) and 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, an inhibitor of guanylate cyclase) did not block the response to lubiprostone. In addition, tetraethylammonium (TEA, a voltage-dependent potassium [K+] channel blocker) and apamin (a calcium [Ca2+]-dependent K+ channel blocker) did not block the response to lubiprostone. However, glibenclamide (an ATP-sensitive K+ channel blocker) blocked the response to lubiprostone. Similar to lubiprostone, pinacidil (an opener of ATP-sensitive K+ channel) hyperpolarized the membrane and inhibited the generation of pacemaker potentials, and these effects were inhibited by glibenclamide. These results suggest that lubiprostone can modulate the pacemaker potentials of colonic ICCs via activation of ATP-sensitive K+ channel through a prostanoid EP receptor-independent mechanism.

Functional expression of mechanosensitive two-pore domain potassium channel in human bladder carcinoma cells / 동물의과학연구지

Bladder cancer is a common cancer in smoking men and may correlate with mechanosensitive potassium channels because the urinary bladder is a stretch sensing organ. Two-pore K+ channels (K2P), such as TASK3 and TREK1, have recently been shown to play a critical role in both cell apoptosis and tumorigenesis. Of the channels, TREK1 can be activated by many physiological stimuli, including polyunsaturated fatty acids, and intracellular pH, hypoxia, and neurotransmitters. Here we attempted to determine whether TREK1 is functionally expressed in bladder cancer 253J cells. K2P channels, including TREK1, TREK2, TASK1, TASK3, and TWIK1, were quantified in cultured human bladder cancer 253J cells using real time quantitative RT-PCR (qRT-PCR) analysis. Among them, TREK1-like channel was recorded at a single channel level using the patch-clamp technique. The TREKl-like channel, with single-channel conductance of ~90 pS at -80 mV, was recorded in symmetrical 150 mM KCl using an excised inside-out patch configuration. The current-voltage relationships were linear and were insensitive to tetraethylammonium. The channel was activated by membrane stretch, free fatty acids, and intracellular acidosis. These results with electrophysiological properties resemble to those of K2P channel, for instance, TREK1. Therefore, we conclude that TREK1 channel is functionally present in bladder cancer 253J cells.

Potassium Currents in Isolated Deiters' Cells of Guinea Pig

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.

Vasorelaxant mechanisms of ketamine in rabbit renal artery / 대한마취과학회지

BACKGROUND: Ketamine is a non-barbiturate anesthetic agent which has various effects on the cardiovascular system. Among them, ketamine is known for its hypotensive properties. The hypotension is thought to be mediated by a direct effect on vascular smooth muscles. This study is designed to examine the effects of ketamine on KCl- and histamine-induced contraction in isolated rabbit renal arteries. METHODS: Endothelium-intact or -denuded smooth muscle rings were prepared and mounted in myographs for isometric tension measurements. The inhibitory effect of ketamine were investigated in smooth muscle rings precontracted with either 50 mM KCl- or 10 microM histamine. RESULTS: Ketamine (0.1-100 microg/ml) produced similar concentration-dependent inhibition of contractile responses induced by either 50 mM KCl or 10 microM histamine. The respective IC50 values measured for ketamine following precontractions by 50 mM KCl and 10 microM histamine were 28.9 microg/ml (105.5 microM) and 26.7 microg/ml (97.5 microM). The inhibitory effect of 30 microg/ml ketamine were similarly observed after removal of endothelium or pretreatment with NG-Nitroarginine Methyl Ester (0.1 mM). The inhibitory effect of 30 microg/ml ketamine on histamine-evoked contraction was reduced by either tetraethylammonium (10 mM) or iberiotoxin, a large conductance Ca2+-activated K+ channel blocker. However, depletion of intracellular Ca2+ stores by ryanodine (10 microM) or thapsigargin (10 microM) showed no significant effect on 30 microg/ml ketamine-induced relaxation. Pre-incubation with 30 microg/ml ketamine significantly inhibited CaCl2-induced contraction at almost all ranges of concentration. CONCLUSIONS: Ketamine-induced relaxation of rabbit renal arteries is mediated by both the activation of large conductance Ca2+-activated K+ channel and the inhibition of Ca2+ influx.

The methyl ester of rosuvastatin elicited an endothelium-independent and 3-hydroxy-3-methylglutaryl coenzyme A reductase-independent relaxant effect in rat aorta

The relaxant effect of the methyl ester of rosuvastatin was evaluated on aortic rings from male Wistar rats (250-300 g, 6 rats for each experimental group) with and without endothelium precontracted with 1.0 µM phenylephrine. The methyl ester presented a slightly greater potency than rosuvastatin in relaxing aortic rings, with log IC50 values of -6.88 and -6.07 M, respectively. Unlike rosuvastatin, the effect of its methyl ester was endothelium-independent. Pretreatment with 10 µM indomethacin did not inhibit, and pretreatment with 1 mM mevalonate only modestly inhibited the relaxant effect of the methyl ester. Nω-nitro-L-arginine methyl ester (L-NAME, 10 µM), the selective nitric oxide-2 (NO-2) inhibitor 1400 W (10 µM), tetraethylammonium (TEA, 10 mM), and cycloheximide (10 µM) partially inhibited the relaxant effect of the methyl ester on endothelium-denuded aortic rings. However, the combination of TEA plus either L-NAME or cycloheximide completely inhibited the relaxant effect. Inducible NO synthase (NOS-2) was only present in endothelium-denuded aortic rings, as demonstrated by immunoblot with methyl ester-treated rings. In conclusion, whereas rosuvastatin was associated with a relaxant effect dependent on endothelium and hydroxymethylglutaryl coenzyme A reductase in rat aorta, the methyl ester of rosuvastatin exhibited an endothelium-independent and only slightly hydroxymethylglutaryl coenzyme A reductase-dependent relaxant effect. Both NO produced by NOS-2 and K+ channels are involved in the relaxant effect of the methyl ester of rosuvastatin.

Mechanism of vasodilation by propofol in the rabbit renal artery

BACKGROUND: Propofol directly inhibits vascular reactivity. However, available information regarding the underlying mechanisms of propofol is poor. Therefore, mechanisms of the underlying relaxant action of propofol were investigated using rabbit renal arteries. METHODS: Propofol-induced relaxation of rabbit renal arteries was studied in contracted preparations with 50 mM KCl or 10microM histamine. Vessel tension was recorded with a pen recorder. We were interested in determining whether propofol-induced vasodilation is affected by endothelium-denudation, L-NG-nitroarginine methyl ester (L-NAME), tetraethylammonium (TEA), iberiotoxin, glibenclamide, 4-aminopyridine, 7-ethoxyresorufin, caffeic acid, baiclalein, ryanodine, and thapsigargin. RESULTS: Propofol-induced concentration-dependent vasodilation was not affected either by endothelium denudation or by L-NAME during histamine-induced contraction. The relaxing effect of propofol on histamine-induced contraction was inhibited by either TEA, a K+ channel inhibitor, or iberiotoxin (100 nM), a selective blocker of the large conductance Ca(2+)-activated K+ channel (BKCa channel). In contrast, the relaxing effect of propofol was unaffected by 10microM glibenclamide, an ATP-sensitive K+ channel blocker, by 5 mM 4-aminopyridine, a blocker of delayed rectifier, by 7-ethoxyresorufin, a cytochrome P450 inhibitor, by 10microM caffeic acid and 10microM baiclalein, lipooxygenase inhibitors, or by 10microM ryanodine and thapsigargin, Ca2+store inhibitors. CONCLUSIONS: These results suggest that the relaxant effect of propofol may result from activation of BKCa channels by inhibiting voltage-gated Ca2+ influx in a prolonged manner.

Effects of Cyclic Nucleotide-Gated Channels in Vestibular Nuclear Neurons / 전남의대학술지

This study was designed to investigate the effects an 8-Br-cGMP on the neuronal activity of rat vestibular nuclear cells. Sprague-Dawley rats aged 14 to 16 days were decapitated under ether anesthesia. After treatment with pronase and thermolysin, the dissociated vestibular nuclear cells 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. Twelve vestibular nuclear cells revealed excitatory responses to 1-5 microM of 8-Br-cGMP, and 3 neurons did not respond to 8-Br-cGMP. Whole potassium currents of vestibular nuclear cells were decreased by 8-Br-cGMP (n=12). After calcium-dependent potassium currents were blocked by tetraethylammonium, the potassium currents were not decreased by 8-Br-cGMP. These experimental results suggest that 8-Br-cGMP changes the neuronal activity of vestibular nuclear cells by blocking the calcium-dependent potassium currents that underlie the afterhyperpolarization.

Quercetin-induced Growth Inhibition in Human Bladder Cancer Cells Is Associated with an Increase in Ca(2+)-activated K+ Channels

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 Ca2+-activated K+ (BKCa) or MaxiK channels were functionally expressed in 253J cells, and quercetin increased BKCa current in a concentration dependent and reversible manner using a whole cell patch configuration. The half maximal activation concentration (IC50) of quercetin was 45.5+/-7.2 microM. The quercetin-evoked BKCa current was inhibited by tetraethylammonium (TEA; 5 mM) a non-specific BKCa blocker and iberiotoxin (IBX; 100 nM) a BKCa-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 (DiBAC4(3); 100 nM). Quercetin-evoked hyperpolarization was prevented by TEA. Quercetin produced an antiproliferative effect (30.3+/-13.5%) which was recovered to 53.3+/-10.5% and 72.9+/-3.7% by TEA and IBX, respectively. Taken together our results indicate that activation of BKCa channels may be considered an important target related to the action of quercetin on human bladder cancer cells.

Nitric Oxide-mediated Relaxation by High K+ in Human Gastric Longitudinal Smooth Muscle

This study was designed to elucidate high-K+induced response of circular and longitudinal smooth muscle from human gastric corpus using isometric contraction. Contraction from circular and longitudinal muscle stripes of gastric corpus greater curvature and lesser curvature were compared. Circular smooth muscle from corpus greater curvature showed high K+ (50 mM)-induced tonic contraction. On the contrary, however, longitudinal smooth muscle strips showed high K+ (50 mM)-induced sustained relaxation. To find out the reason for the discrepancy we tested several relaxation mechanisms. Protein kinase blockers like KT5720, PKA inhibitor, and KT5823, PKG inhibitor, did not affect high K+-induced relaxation. K+ channel blockers like tetraethylammonium (TEA), apamin (APA), glibenclamide (Glib) and barium (Ba2+) also had no effect. However, N(G)-nitro-L-arginine (L-NNA) and 1H-(1,2,4) oxadiazolo (4,3-A) quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase (sGC) and 4-AP (4-aminopyridine), voltage-dependent K+ channel (KV) blocker, inhibited high K+-induced relaxation, hence reversing to tonic contraction. High K+-induced relaxation was observed in gastric corpus of human stomach, but only in the longitudinal muscles from greater curvature not lesser curvature. L-NNA, ODQ and KV channel blocker sensitive high K+-induced relaxation in longitudinal muscle of higher portion of corpus was also observed. These results suggest that longitudinal smooth muscle from greater curvature of gastric corpus produced high K+-induced relaxation which was activated by NO/sGC pathway and by KV channel dependent mechanism.

Effects of Cyclic Nucleotide-Gated Channels in Vestibular Nuclear Neurons / 전남의대학술지

This study was designed to investigate the effects an 8-Br-cGMP on the neuronal activity of rat vestibular nuclear cells. Sprague-Dawley rats aged 14 to 16 days were decapitated under ether anesthesia. After treatment with pronase and thermolysin, the dissociated vestibular nuclear cells 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. Twelve vestibular nuclear cells revealed excitatory responses to 1-5 microM of 8-Br-cGMP, and 3 neurons did not respond to 8-Br-cGMP. Whole potassium currents of vestibular nuclear cells were decreased by 8-Br-cGMP (n=12). After calcium-dependent potassium currents were blocked by tetraethylammonium, the potassium currents were not decreased by 8-Br-cGMP. These experimental results suggest that 8-Br-cGMP changes the neuronal activity of vestibular nuclear cells by blocking the calcium-dependent potassium currents that underlie the afterhyperpolarization.

Inhibition of Hypoxic Pulmonary Vasoconstriction of Rats by Carbon Monoxide

Hypoxic pulmonary vasoconstriction (HPV), a unique response of pulmonary circulation, is critical to prevent hypoxemia under local hypoventilation. Hypoxic inhibition of K+ channel is known as an important O2-sensing mechanism in HPV. Carbon monoxide (CO) is suggested as a positive regulator of Ca2+-activated K+ channel (BK(Ca)), a stimulator of guanylate cyclase, and an O2-mimetic agent in heme moiety-dependent O2 sensing mechanisms. Here we compared the effects of CO on the HPV (Po2, 3%) in isolated pulmonary artery (HPV(PA)) and in blood-perfused/ventilated lungs (HPV(lung)) of rats. A pretreatment with CO (3%) abolished the HPV(PA) in a reversible manner. The inhibition of HPV(PA) was completely reversed by 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ), a guanylate cyclase inhibitor. In contrast, the HPV(lung) was only partly decreased by CO. Moreover, the partial inhibition of HPV(lung) by CO was affected neither by the pretreatment with ODQ nor by NO synthase inhibitor (L-NAME). The CO-induced inhibitions of HPV(PA) and HPV(lung) were commonly unaffected by tetraethylammonium (TEA, 2 mM), a blocker of BK(Ca). As a whole, CO inhibits HPV(PA) via activating guanylate cyclase. The inconsistent effects of ODQ on HPV(PA) and HPV(lung) suggest that ODQ may lose its sGC inhibitory action when applied to the blood-containing perfusate.

The Effect of Hypoxia on the Release of Endothelium-derived Relaxing Factor in Rabbit Thoracic Aorta / 대한흉부외과학회지

BACKGROUND: To clarify the effect of hypoxia on vascular contractility, we tried to show whether hypoxia induced the release of endothelium-derived relaxing factor (EDRF) and the nature of the underlying mechanism for this release. MATERIAL AND METHOD: Isometric contractions were observed in rabbit aorta, and the released EDRF from the rabbit aorta was bioassayed by using rabbit denuded carotid artery. The intracellular Ca2+ concentration ([Ca2+]i) in the cultured rabbit aortic endothelial cells was recorded by a microfluorimeter with using Fura-2/AM. Hypoxia was evoked to the blood vessels or endothelial cells by eliminating the O2 in the aerating gases in the external solution. Chemical hypoxia was evoked by applying deoxyglucose or CN-. RESULT: Hypoxia relaxed the precontracted rabbit thoracic aorta that had its endothelium, and the magnitude of the relaxation was gradually increased by repetitive bouts of hypoxia. In contrast, hypoxia-induced relaxation was not evoked in the aorta that was denuded of endothelium. In a bioassay experiment, hypoxia released endothelium-derived relaxing factor (EDRF) and the release was inhibited by L-NAME or the K+ channel blocker tetraethylammonium (TEA). In the cultured endothelial cells, hypoxia augmented the ATP-induced increase of the intracellular Ca2+ concentration ([Ca2+]i) and this increase was inhibited by TEA. Furthermore, chemical hypoxia also increased the Ca2+ influx. CONCLUSION: From these results, it can be concluded that hypoxia might induce the release of NO from rabbit aortic endothelial cells by increasing [Ca2+]i.

Ca2+-activated K+ Current in Freshly Isolated c-Kit Positive Cells in Guinea-pig Stomach

This study was designed to isolate Ca2+-activated K+ current (IKCa) and elucidate its physiological significance in freshly isolated interstitial cells of Cajal (ICCs) of guinea-pig stomach. Single ICC was freshly isolated by enzymatically dissociating from myenteric border of gastric antrum free of circular muscles, and conventional whole-cell voltage clamp technique including immunohistochemical techniques were employed to characterize the cells: In myenteric border of gastric antrum, ICC-MY (ICCs from myenteric border) were detected by immunohistochemical reactivity, and single ICC-MY which has many branches was immunohistochemically c-Kit positive. Under K+-rich and 0.1 mM ethylene glycol-bis (2-aminoethyl ether)-N,N,N',N'-tetraacetic acid pipette solution, ICC produced spontaneous inward current (-256+/-92.2 pA). When step-depolarizing pulse from -80 to +80 mV was applied at holding potential (Vh) of -80 mV, voltage-dependent outward currents were recorded with superimposed spontaneous transient outward currents (STOCs). Both STOCs and outward currents were reversibly affected by tetraethylammonium chloride (TEA) and iberiotoxin (IbTX); 2 mM TEA and 200 nM IbTX completely abolished STOCs and significantly inhibited outward K+ current over the whole potential range tested for current/voltage (I/V) relationship. In addition, TEA delayed repolarization phase of spontaneous inward current. The present results indicate the presence of IKCa in a single ICC, and it might be involved in regulation of repolarizing phase of spontaneous inward current in guinea-pig stomach.