Echinacoside, an active compound in the herb Herba Cistanche, has been reported to inhibit glutamate release. In this study, we investigated the effects of echinacoside on spontaneous excitatory synaptic transmission changes induced by 4-aminopyridine (4-AP), by using the in vitro rat hippocampal slice technique and whole-cell patch clamp recordings from CA3 pyramidal neurons. Perfusion with echinacoside significantly suppressed the 4-AP-induced epileptiform activity in a concentration-dependent manner. Echinacoside reduced 4-AP-induced increase in frequency of spontaneous excitatory postsynaptic currents (sEPSCs) but it did not affect the amplitude of sEPSCs or glutamate-activated currents, implicating a presynaptic mechanism of action. Echinacoside also potently blocked sustained repetitive firing, which is a basic mechanism of antiepileptic drugs. These results suggest that echinacoside exerts an antiepileptic effect on hippocampal CA3 pyramidal neurons by simultaneously decreasing glutamate release and blocking abnormal firing synchronization. Accordingly, our study provides experimental evidence that echinacoside may represent an effective pharmacological agent for treating epilepsy.
4-Aminopyridine ; Animals ; Anticonvulsants ; Cistanche* ; Epilepsy ; Excitatory Postsynaptic Potentials ; Fires ; Glutamic Acid ; Hippocampus ; In Vitro Techniques ; Perfusion ; Pyramidal Cells* ; Rats ; Synaptic Transmission

PURPOSE: We studied the effects of alcohol administration on the corpus cavernosum (CC) using an animal model. MATERIALS AND METHODS: CC sections and the aortic ring of rabbits were used in an organ bath study. After acute alcohol administration, changes in blood alcohol concentration and electrical stimulation induced intracavernosal pressure/mean arterial pressure (ICP/MAP) percentage were compared in rats. Cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) levels in the CC were measured using immunoassays. After chronic alcohol administration, ICP/MAP percentage, cAMP and cGMP were compared in rats. Histological changes were examined using the Masson trichrome stain and the Sircol collagen assay. Endothelial nitric oxide synthase (eNOS) expression was examined using immunohistochemistry and Western blotting. RESULTS: Alcohol relaxed the CC in a dose-dependent manner, and the relaxation response was suppressed when pretreated with propranolol, indomethacin, glibenclamide, and 4-aminopyridine. In rats with acute alcohol exposure, the cAMP level in the CC was significantly greater than was observed in the control group (p<0.05). In rats with chronic alcohol exposure, however, changes in cAMP and cGMP levels were insignificant, and the CC showed markedly smaller areas of smooth muscle, greater amounts of dense collagen (p<0.05). Immunohistochemical analysis of eNOS showed a less intense response, and western blotting showed that eNOS expression was significantly lower in this group (p<0.05). CONCLUSIONS: Acute alcohol administration activated the cAMP pathway with positive effects on erectile function. In contrast, chronic alcohol administration changed the ultrastructures of the CC and suppressed eNOS expression, thereby leading to erectile dysfunction.
4-Aminopyridine ; Adenosine Monophosphate ; Animals ; Arterial Pressure ; Baths ; Blood Alcohol Content ; Blotting, Western ; Collagen ; Cyclic AMP ; Electric Stimulation ; Erectile Dysfunction ; Glyburide ; Guanosine Monophosphate ; Immunoassay ; Immunohistochemistry ; Indomethacin ; Male ; Models, Animal ; Muscle, Smooth ; Nitric Oxide Synthase Type III ; Penile Erection ; Propranolol ; Rabbits ; Rats ; Relaxation

Plasma membrane hyperpolarization associated with activation of Ca²⁺-activated K⁺ channels plays an important role in sperm capacitation during fertilization. Although Slo3 (slowpoke homologue 3), together with the auxiliary γ2-subunit, LRRC52 (leucine-rich-repeat–containing 52), is known to mediate the pH-sensitive, sperm-specific K⁺ current KSper in mice, the molecular identity of this channel in human sperm remains controversial. In this study, we tested the classical BK(Ca) activators, NS1619 and LDD175, on human Slo3, heterologously expressed in HEK293 cells together with its functional interacting γ2 subunit, hLRRC52. As previously reported, Slo3 K⁺ current was unaffected by iberiotoxin or 4-aminopyridine, but was inhibited by ~50% by 20 mM TEA. Extracellular alkalinization potentiated hSlo3 K⁺ current, and internal alkalinization and Ca²⁺ elevation induced a leftward shift its activation voltage. NS1619, which acts intracellularly to modulate hSlo1 gating, attenuated hSlo3 K⁺ currents, whereas LDD175 increased this current and induced membrane potential hyperpolarization. LDD175-induced potentiation was not associated with a change in the half-activation voltage at different intracellular pHs (pH 7.3 and pH 8.0) in the absence of intracellular Ca²⁺. In contrast, elevation of intracellular Ca²⁺ dramatically enhanced the LDD175-induced leftward shift in the half-activation potential of hSlo3. Therefore, the mechanism of action does not involve pH-dependent modulation of hSlo3 gating; instead, LDD175 may modulate Ca²⁺-dependent activation of hSlo3. Thus, LDD175 potentially activates native KSper and may induce membrane hyperpolarization-associated hyperactivation in human sperm.
4-Aminopyridine ; Animals ; Cell Membrane ; Fertilization ; HEK293 Cells ; Humans ; Hydrogen-Ion Concentration ; Membrane Potentials ; Membranes ; Mice ; Potassium Channels, Calcium-Activated* ; Sperm Capacitation ; Sperm Motility ; Spermatozoa ; Tea

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.
4-Aminopyridine ; Baths ; Calcium ; Calcium Chloride ; Glyburide ; Humans* ; Potassium Channels* ; Potassium Chloride ; Potassium* ; Radial Artery* ; Relaxation ; Serotonin ; Taurine* ; Tetraethylammonium ; Vasodilation

BACKGROUND: The plant-derived estrogen biochanin A is known to cause vasodilation, but its mechanism of action in hypertension remains unclear. This study was undertaken to investigate the effects and mechanisms of biochanin A on the thoracic aorta in two-kidney, one clip (2K1C) renovascular hypertensive rats. METHODS: Hypertension was induced by clipping the left renal artery, and control age-matched rats were sham treated. Thoracic aortae were mounted in tissue baths to measure isometric tension. RESULTS: Biochanin A caused concentration-dependent relaxation in aortic rings from 2K1C hypertensive and sham-treated rats, which was greater in 2K1C rats than in sham rats. Biochanin A-induced relaxation was significantly attenuated by removing the endothelium in aortic rings from 2K1C rats, but not in sham rats. Nomega-Nitro-L-arginine methylester, a nitric oxide synthase inhibitor, or indomethacin, a cyclooxygenase inhibitor, did not affect the biochanin A-induced relaxation in aortic rings from 2K1C and sham rats. By contrast, treatment with glibenclamide, a selective inhibitor of adenosine triphosphate-sensitive K+ channels, ortetraethy-lammonium, an inhibitor of Ca2+-activated K+ channels, significantly reduced biochanin A-induced relaxation in aortic rings from both groups. However, 4-aminopyridine, a selective inhibitor of voltage-dependent K+ channels, inhibited the relaxation induced by biochanin A in 2K1C rats, whereas no significant differences were observed in sham rats. CONCLUSION: These results suggest that the enhanced relaxation caused by biochanin A in aortic rings from hypertensive rats is endothelium dependent. Vascular smooth muscle K+ channels may be involved in biochanin A-induced relaxation in aortae from hypertensive and normotensive rats. In addition, an endothelium-derived activation of voltage-dependent K+ channels contributes, at least in part, to the relaxant effect of biochanin A in renovascular hypertension.
4-Aminopyridine ; Adenosine ; Animals ; Aorta ; Aorta, Thoracic ; Baths ; Endothelium ; Estrogens ; Glyburide ; Hypertension ; Hypertension, Renovascular ; Indomethacin ; Muscle, Smooth, Vascular ; Nitric Oxide Synthase ; Phytoestrogens* ; Potassium Channels, Calcium-Activated ; Prostaglandin-Endoperoxide Synthases ; Rats* ; Relaxation ; Renal Artery ; Vasodilation*

BACKGROUND: A toxic dose of bupivacaine produces vasodilation in isolated aortas. The goal of this in vitro study was to investigate the cellular mechanism associated with bupivacaine-induced vasodilation in isolated endotheliumdenuded rat aortas precontracted with phenylephrine. METHODS: Isolated endothelium-denuded rat aortas were suspended for isometric tension recordings. The effects of nifedipine, verapamil, iberiotoxin, 4-aminopyridine, barium chloride, and glibenclamide on bupivacaine concentration-response curves were assessed in endothelium-denuded aortas precontracted with phenylephrine. The effect of phenylephrine and KCl used for precontraction on bupivacaine-induced concentration-response curves was assessed. The effects of verapamil on phenylephrine concentration-response curves were assessed. The effects of bupivacaine on the intracellular calcium concentration ([Ca2+]i) and tension in aortas precontracted with phenylephrine were measured simultaneously with the acetoxymethyl ester of a fura-2-loaded aortic strip. RESULTS: Pretreatment with potassium channel inhibitors had no effect on bupivacaine-induced relaxation in the endothelium-denuded aortas precontracted with phenylephrine, whereas verapamil or nifedipine attenuated bupivacaine-induced relaxation. The magnitude of the bupivacaine-induced relaxation was enhanced in the 100 mM KCl-induced precontracted aortas compared with the phenylephrine-induced precontracted aortas. Verapamil attenuated the phenylephrine-induced contraction. The magnitude of the bupivacaine-induced relaxation was higher than that of the bupivacaine-induced [Ca2+]i decrease in the aortas precontracted with phenylephrine. CONCLUSIONS: Taken together, these results suggest that toxic-dose bupivacaine-induced vasodilation appears to be mediated by decreased calcium sensitization in endothelium-denuded aortas precontracted with phenylephrine. In addition, potassium channel inhibitors had no effect on bupivacaine-induced relaxation. Toxic-dose bupivacaine- induced vasodilation may be partially associated with the inhibitory effect of voltage-operated calcium channels.
4-Aminopyridine ; Animals ; Aorta* ; Barium ; Bupivacaine ; Calcium Channels ; Calcium* ; Glyburide ; Nifedipine ; Phenylephrine* ; Potassium Channels ; Rats* ; Relaxation ; Vasodilation* ; Verapamil

Aminopyridines are potassium channel blockers that increase the excitability of nerve cells and axons; therefore, they are widely used to treat different neurological disorders. Here we present a patient with idiopathic downbeat nystagmus and lower urinary tract symptoms (LUTS) due to benign prostatic hyperplasia who was treated with the sustained-release form of 4-aminopyridine (4-AP). During treatment with 4-AP, the LUTS improved. This improvement was monitored by using uroflowmetry and the International Prostate Symptom Score. A significant improvement of symptoms was observed in relation to the voided volume. This included an improved emptying of the bladder without an increase in residual urine. In animal studies, both nonselective K+ channel blockade and selective voltage-sensitive potassium blockade by 4-AP resulted in increased contraction on rat detrusor strips. To our knowledge, this is the first clinical observation of the mode of action of 4-AP in urological symptoms in humans.
4-Aminopyridine* ; Aminopyridines ; Animals ; Axons ; Drug Therapy ; Humans ; Lower Urinary Tract Symptoms* ; Nervous System Diseases ; Neurons ; Potassium ; Potassium Channel Blockers ; Prostate ; Prostatic Hyperplasia* ; Rats ; Urinary Bladder ; Urinary Bladder, Neurogenic

Serotonin (5-hydroxytryptamine (5-HT)) is a neurotransmitter that regulates a variety of functions in the nervous, gastrointestinal and cardiovascular systems. Despite such importance, 5-HT signaling pathways are not entirely clear. We demonstrated previously that 4-aminopyridine (4-AP)-sensitive voltage-gated K+ (Kv) channels determine the resting membrane potential of arterial smooth muscle cells and that the Kv channels are inhibited by 5-HT, which depolarizes the membranes. Therefore, we hypothesized that 5-HT contracts arteries by inhibiting Kv channels. Here we studied 5-HT signaling and the detailed role of Kv currents in rat mesenteric arteries using patch-clamp and isometric tension measurements. Our data showed that inhibiting 4-AP-sensitive Kv channels contracted arterial rings, whereas inhibiting Ca2+-activated K+, inward rectifier K+ and ATP-sensitive K+ channels had little effect on arterial contraction, indicating a central role of Kv channels in the regulation of resting arterial tone. 5-HT-induced arterial contraction decreased significantly in the presence of high KCl or the voltage-gated Ca2+ channel (VGCC) inhibitor nifedipine, indicating that membrane depolarization and the consequent activation of VGCCs mediate the 5-HT-induced vasoconstriction. The effects of 5-HT on Kv currents and arterial contraction were markedly prevented by the 5-HT2A receptor antagonists ketanserin and spiperone. Consistently, alpha-methyl 5-HT, a 5-HT2 receptor agonist, mimicked the 5-HT action on Kv channels. Pretreatment with a Src tyrosine kinase inhibitor, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine, prevented both the 5-HT-mediated vasoconstriction and Kv current inhibition. Our data suggest that 4-AP-sensitive Kv channels are the primary regulator of the resting tone in rat mesenteric arteries. 5-HT constricts the arteries by inhibiting Kv channels via the 5-HT2A receptor and Src tyrosine kinase pathway.
4-Aminopyridine/pharmacology ; Action Potentials ; Animals ; Calcium Channel Blockers/pharmacology ; Calcium Channels/metabolism ; Cells, Cultured ; Ketanserin/pharmacology ; Male ; Mesenteric Arteries/drug effects/*metabolism/physiology ; Muscle Contraction ; Muscle, Smooth, Vascular/cytology/drug effects/metabolism/physiology ; Myocytes, Smooth Muscle/drug effects/metabolism/physiology ; Nifedipine/pharmacology ; Potassium Channel Blockers/pharmacology ; Potassium Channels, Voltage-Gated/antagonists & inhibitors/*metabolism ; Protein Kinase Inhibitors/pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptor, Serotonin, 5-HT2A/*metabolism ; Serotonin/*pharmacology ; Serotonin 5-HT2 Receptor Antagonists/pharmacology ; Spiperone/pharmacology ; *Vasoconstriction ; src-Family Kinases/antagonists & inhibitors/*metabolism

The study aimed to investigate the age-related changes and drug reactions of transient outward potassium current (Ito) of ventricular myocytes. Twenty-eight Sprague Dawley rats were divided into young (3-5 months), adult (13-15 months) and aged (22-24 months) groups, and Ito currents of isolated myocytes from each group were recorded respectively by patch-clamp. The perfusion of 2.0 mmol/L 4-AP or 1.0 μmol/L isoproterenol was added respectively in each group, and the changes of Ito were observed. In comparison with young and adult groups, Ito densities of ventricular myocytes in aged group was significantly increased, the curve of steady-state activation of Ito shifted to the left, the close-state inactivation rate significantly decreased, and recovery rate from the steady-state inactivation became quicker. However, no significant changes could be detected for the Ito steady-state inactivation of ventricular myocytes in aged group. The similar responsiveness to 4-AP was observed in all three groups, but the responsiveness to isoproterenol was weaker in the aged group (55.9%) than in the other two groups (127.5% and 125.8%). In conclusion, the results show that Ito of rat ventricular myocyte of aging heart has increased current density and decreased response to isoproterenol.
4-Aminopyridine ; pharmacology ; Aging ; Animals ; Cells, Cultured ; Heart Ventricles ; cytology ; Isoproterenol ; pharmacology ; Myocytes, Cardiac ; physiology ; Potassium Channels ; physiology ; Rats ; Rats, Sprague-Dawley

Acute hypoxia induces contraction of pulmonary artery (PA) to protect ventilation/perfusion mismatch in lungs. As for the cellular mechanism of hypoxic pulmonary vasoconstriction (HPV), hypoxic inhibition of voltage-gated K+ channel (Kv) in PA smooth muscle cell (PASMC) has been suggested. In addition, our recent study showed that thromboxane A2 (TXA2) and hypoxia-activated nonselective cation channel (I(NSC)) is also essential for HPV. However, it is not well understood whether HPV is maintained in the animals exposed to ambient hypoxia for two days (2d-H). Specifically, the associated electrophysiological changes in PASMCs have not been studied. Here we investigate the effects of 2d-H on HPV in isolated ventilated/perfused lungs (V/P lungs) from rats. HPV was almost abolished without structural remodeling of PA in 2d-H rats, and the lost HPV was not recovered by Kv inhibitor, 4-aminopyridine. Patch clamp study showed that the hypoxic inhibition of Kv current in PASMC was similar between 2d-H and control. In contrast, hypoxia and TXA2-activated I(NSC) was not observed in PASMCs of 2d-H. From above results, it is suggested that the decreased I(NSC) might be the primary functional cause of HPV disappearance in the relatively early period (2 d) of hypoxia.
4-Aminopyridine ; Animals ; Anoxia* ; Lung ; Muscle Cells* ; Myocytes, Smooth Muscle ; Pulmonary Artery ; Rats* ; Thromboxane A2 ; Vasoconstriction*