Modulating Hyperpolarization-Activated Cation Currents through Small Molecule Perturbations: Magnitude and Gating Control.

The hyperpolarization-activated cation current (Ih) exhibits a slowly activating time course of the current (Ih) when the cell membrane is hyperpolarized for an extended duration. It is involved in generating electrical activity in various excitable cells. Numerous structurally distinct compounds or herbal drugs have the potential to impact both the magnitude and gating kinetics of this current. Brivaracetam, a chemical analog of levetiracetam known to be a ligand for synaptic vesicle protein 2A, could directly suppress the Ih magnitude. Carisbamate, an anticonvulsant agent, not only inhibited the Ih amplitude but also reduced the strength of voltage-dependent hysteresis (Hys(V)) associated with Ih. Cilobradine, similar to ivabradine, inhibited the amplitude of Ih; however, it also suppressed the amplitude of delayed-rectifier K+ currents. Dexmedetomidine, an agonist of α2-adrenergic receptor, exerted a depressant action on Ih in a concentration-dependent fashion. Suppression of Ih amplitude was observed when GAL-021, a breathing control modulator, was present at a concentration exceeding 30 µM. Lutein, one of the few xanthophyll carotenoids, was able to suppress the Ih amplitude as well as to depress Hys(V)'s strength of Ih. Pirfenidone, a pyridine derivative known to be an anti-fibrotic agent, depressed the Ih magnitude in a concentration- and voltage-dependent fashion. Tramadol, a synthetic centrally active analgesic, was shown to reduce the Ih magnitude, independent of its interaction with opioid receptors. Various herbal drugs, including ent-kaurane-type diterpenoids from Croton tonkinensis, Ganoderma triterpenoids, honokiol, and pterostilbene, demonstrated efficacy in reducing the magnitude of Ih. Conversely, oxaliplatin, a platinum-based chemotherapeutic compound, was observed to effectively increase the Ih amplitude. Collectively, the regulatory effects of these compounds or herbal drugs on cellular function can be partly attributed to their perturbations on Ih.

Cilostazol eliminates radiation-resistant glioblastoma by re-evoking big conductance calcium-activated potassium channel activity.

In spite of radio- and chemotherapy, glioblastoma (GBM) develops therapeutic resistance leading to recurrence and poor prognosis. Therefore, understanding the underlying mechanisms of resistance is important to improve the treatment of GBM. To this end, we developed a radiation-resistant cell model by exposure to consecutive periods of irradiation. Simultaneously, single high-dose irradiation was introduced to determine "when" GBM developed consecutive irradiation-induced resistance (CIIR). We found that CIIR promoted TGF-ß secretion, activated pro-survival Akt, and downregulated p21 in a p53-independent manner. Furthermore, CIIR upregulated multidrug-resistant proteins, resulting in temozolomide resistance. CIIR GBM also enhanced cell mobility and accelerated cell proliferation. The big-conductance calcium-activated potassium channel (BK channel) is highly expressed and activated in GBM. However, CIIR diminishes BK channel activity in an expression-independent manner. Cilostazol is a phosphodiesterase-3 inhibitor for the treatment of intermittent claudication and was able to reverse CIIR-induced BK channel inactivation. Paxilline, a BK channel blocker, promoted cell migration and proliferation in parental GBM cells. In contrast, Cilostazol inhibited CIIR-induced cell motility, proliferation, and the ability to form tumor spheres. Moreover, we established a radiation-resistant GBM in vivo model by intracranially injecting CIIR GBM cells into the brains of NOD/SCID mice. We found that Cilostazol delayed tumor in vivo growth and prolonged survival. As such, inactivation of the BK channel assists GBM in developing radiation resistance. Accordingly, restoring BK channel activity may be an effective strategy to improve therapeutic efficacy, and cilostazol could be repurposed to treat GBM.

Permissive Modulation of Sphingosine-1-Phosphate-Enhanced Intracellular Calcium on BKCa Channel of Chromaffin Cells.

Sphingosine-1-phosphate (S1P), is a signaling sphingolipid which acts as a bioactive lipid mediator. We assessed whether S1P had multiplex effects in regulating the large-conductance Ca2+-activated K+ channel (BKCa) in catecholamine-secreting chromaffin cells. Using multiple patch-clamp modes, Ca2+ imaging, and computational modeling, we evaluated the effects of S1P on the Ca2+-activated K+ currents (IK(Ca)) in bovine adrenal chromaffin cells and in a pheochromocytoma cell line (PC12). In outside-out patches, the open probability of BKCa channel was reduced with a mean-closed time increment, but without a conductance change in response to a low-concentration S1P (1 µM). The intracellular Ca2+ concentration (Cai) was elevated in response to a high-dose (10 µM) but not low-dose of S1P. The single-channel activity of BKCa was also enhanced by S1P (10 µM) in the cell-attached recording of chromaffin cells. In the whole-cell voltage-clamp, a low-dose S1P (1 µM) suppressed IK(Ca), whereas a high-dose S1P (10 µM) produced a biphasic response in the amplitude of IK(Ca), i.e., an initial decrease followed by a sustained increase. The S1P-induced IK(Ca) enhancement was abolished by BAPTA. Current-clamp studies showed that S1P (1 µM) increased the action potential (AP) firing. Simulation data revealed that the decreased BKCa conductance leads to increased AP firings in a modeling chromaffin cell. Over a similar dosage range, S1P (1 µM) inhibited IK(Ca) and the permissive role of S1P on the BKCa activity was also effectively observed in the PC12 cell system. The S1P-mediated IK(Ca) stimulation may result from the elevated Cai, whereas the inhibition of BKCa activity by S1P appears to be direct. By the differentiated tailoring BKCa channel function, S1P can modulate stimulus-secretion coupling in chromaffin cells.

Gastrodin alleviates seizure severity and neuronal excitotoxicities in the rat lithium-pilocarpine model of temporal lobe epilepsy via enhancing GABAergic transmission.

ETHNOPHARMACOLOGICAL RELEVANCE: Temporal lobe epilepsy remains one of the most drug-resistant focal epilepsy, leading to enormous healthcare burden. Among traditional herb medicine, some ingredients have the potential to treat seizure and alleviate the neuronal excitoxicity. The dried rhizome of Gastrodia elata Blume has been used to treat convulsive disorder, dizziness, dementia and migraine in eastern Asia. AIM OF THE STUDY: To determine whether gastrodin, an active ingredient of Gastrodia elata Blume, can reduce lithium-pilocarpine induced seizure severity and neuronal excitotoxicity and explore the underlying mechanism. MATERIALS AND METHODS: We divided the Sprague-Dawley rats into an experimental group (gastrodin group) and a control group (Dimethyl sulfoxide, vehicle group) and performed the behavioral analysis and electroencephalography to determine the effect of gastrodin on the seizure severity induced by lithium-pilocarpine injection. Nissl-stained histopathology elucidated the degree of rat hippocampal neuronal damage as markers of acute and subacute neuronal excitotoxicity. Besides, the Western blotting of dissected hippocampus was carried out to demonstrate the protein expression involving GABAergic transmission and metabolic pathway. RESULTS: Gastrodin reduced the acute seizure severity in lithium-pilocarpine-induced seizure model. In electroencephalography recording, gastrodin exerted inhibitory action on epileptiform discharge. Compared with control group, gastrodin exhibited neuroprotective effect against seizure related hippocampal neuronal damage at acute and subacute stages. The Western blotting showed that gastrodin reversed the degradation of GABAA receptor after pilocarpine-induced seizures. CONCLUSIONS: In the experimental seizure model, gastrodin showed anti-seizure and neuroprotective abilities. Enhancing the expression of GABAA receptor plays an important role in its antiepileptic mechanism. The results offer a new insight of developing new antiepileptic drugs from traditional Chinese medicine.

Effects of Sesamin, the Major Furofuran Lignan of Sesame Oil, on the Amplitude and Gating of Voltage-Gated Na+ and K+ Currents.

Sesamin (SSM) and sesamolin (SesA) are the two major furofuran lignans of sesame oil and they have been previously noticed to exert various biological actions. However, their modulatory actions on different types of ionic currents in electrically excitable cells remain largely unresolved. The present experiments were undertaken to explore the possible perturbations of SSM and SesA on different types of ionic currents, e.g., voltage-gated Na+ currents (INa), erg-mediated K+ currents (IK(erg)), M-type K+ currents (IK(M)), delayed-rectifier K+ currents (IK(DR)) and hyperpolarization-activated cation currents (Ih) identified from pituitary tumor (GH3) cells. The exposure to SSM or SesA depressed the transient and late components of INa with different potencies. The IC50 value of SSM needed to lessen the peak or sustained INa was calculated to be 7.2 or 0.6 µM, while that of SesA was 9.8 or 2.5 µM, respectively. The dissociation constant of SSM-perturbed inhibition on INa, based on the first-order reaction scheme, was measured to be 0.93 µM, a value very similar to the IC50 for its depressant action on sustained INa. The addition of SSM was also effective at suppressing the amplitude of resurgent INa. The addition of SSM could concentration-dependently inhibit the IK(M) amplitude with an IC50 value of 4.8 µM. SSM at a concentration of 30 µM could suppress the amplitude of IK(erg), while at 10 µM, it mildly decreased the IK(DR) amplitude. However, the addition of neither SSM (10 µM) nor SesA (10 µM) altered the amplitude or kinetics of Ih in response to long-lasting hyperpolarization. Additionally, in this study, a modified Markovian model designed for SCN8A-encoded (or NaV1.6) channels was implemented to evaluate the plausible modifications of SSM on the gating kinetics of NaV channels. The model demonstrated herein was well suited to predict that the SSM-mediated decrease in peak INa, followed by increased current inactivation, which could largely account for its favorable decrease in the probability of the open-blocked over open state of NaV channels. Collectively, our study provides evidence that highlights the notion that SSM or SesA could block multiple ion currents, such as INa and IK(M), and suggests that these actions are potentially important and may participate in the functional activities of various electrically excitable cells in vivo.

Effectiveness in the Block by Honokiol, a Dimerized Allylphenol from Magnolia Officinalis, of Hyperpolarization-Activated Cation Current and Delayed-Rectifier K+ Current.

Background: Honokiol (HNK), a dimer of allylphenol obtained from the bark of Magnolia officinalis was demonstrated to exert an array of biological actions in different excitable cell types. However, whether or how this compound can lead to any perturbations on surface-membrane ionic currents remains largely unknown. Methods: We used the patch clamp method and found that addition of HNK effectively depressed the density of macroscopic hyperpolarization-activated cation currents (Ih) in pituitary GH3 cells in a concentration-, time- and voltage-dependent manner. By the use of a two-step voltage protocol, the presence of HNK (10 µM) shifted the steady-state activation curve of Ih density along the voltage axis to a more negative potential by approximately 11 mV, together with no noteworthy modification in the gating charge of the current. Results: The voltage-dependent hysteresis of Ih density elicited by long-lasting triangular ramp pulse was attenuated by the presence of HNK. The HNK addition also diminished the magnitude of deactivating Ih density elicited by ramp-up depolarization with varying durations. The effective half-maximal concentration (IC50) value needed to inhibit the density of Ih or delayed rectifier K+ current identified in GH3 cells was estimated to be 2.1 or 6.8 µM, respectively. In cell-attached current recordings, HNK decreased the frequency of spontaneous action currents. In Rolf B1.T olfactory sensory neurons, HNK was also observed to decrease Ih density in a concentration-dependent manner. Conclusions: The present study highlights the evidence revealing that HNK has the propensity to perturb these ionic currents and that the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel is proposed to be a potential target for the in vivo actions of HNK and its structurally similar compounds.

Characterization of Inhibitory Effectiveness in Hyperpolarization-Activated Cation Currents by a Group of ent-Kaurane-Type Diterpenoids from Croton tonkinensis.

Croton is an extensive flowering plant genus in the spurge family, Euphorbiaceae. Three croton compounds with the common ent-kaurane skeleton have been purified from Croton tonkinensis. METHODS: We examined any modifications of croton components (i.e., croton-01 [ent-18-acetoxy-7α-hydroxykaur-16-en-15-one], croton-02 [ent-7α,14ß-dihydroxykaur-16-en-15-one] and croton-03 [ent-1ß-acetoxy-7α,14ß-dihydroxykaur-16-en-15-one] on either hyperpolarization-activated cation current (Ih) or erg-mediated K+ current identified in pituitary tumor (GH3) cells and in rat insulin-secreting (INS-1) cells via patch-clamp methods. RESULTS: Addition of croton-01, croton-02, or croton-03 effectively and differentially depressed Ih amplitude. Croton-03 (3 µM) shifted the activation curve of Ih to a more negative potential by approximately 11 mV. The voltage-dependent hysteresis of Ih was also diminished by croton-03 administration. Croton-03-induced depression of Ih could not be attenuated by SQ-22536 (10 µM), an inhibitor of adenylate cyclase, but indeed reversed by oxaliplatin (10 µM). The Ih in INS-1 cells was also depressed effectively by croton-03. CONCLUSION: Our study highlights the evidence that these ent-kaurane diterpenoids might conceivably perturb these ionic currents through which they have high influence on the functional activities of endocrine or neuroendocrine cells.

Characterization of the Inhibitory Effect of Gastrodigenin and Gastrodin on M-type K+ Currents in Pituitary Cells and Hippocampal Neurons.

Gastrodigenin (HBA) and gastrodin (GAS) are phenolic ingredients found in Gastrodia elata Blume (GEB), a traditional Chinese herbal medicine. These compounds have been previously used to treat cognitive dysfunction, convulsion, and dizziness. However, at present, there is no available information regarding their potential ionic effects in electrically excitable cells. In the current study, the possible effects of HBA and GAS on different ionic currents in pituitary GH3 cells and hippocampal mHippoE-14 neurons were investigated using the patch-clamp technique. The addition of HBA or GAS resulted in the differential inhibition of the M-type K+ current (IK(M)) density in a concentration-dependent manner in GH3 cells. HBA resulted in a slowing of the activation time course of IK(M), while GAS elevated it. HBA also mildly suppressed the density of erg-mediated or the delayed-rectifier K+ current in GH3 cells. Neither GAS nor HBA (10 µM) modified the voltage-gated Na+ current density, although they suppressed the L-type Ca2+ current density at the same concentration. In hippocampal mHippoE-14 neurons, HBA was effective at inhibiting IK(M) density as well as slowing the activation time course. Taken together, the present study provided the first evidence that HBA or GAS could act on cellular mechanisms, and could therefore potentially have a functional influence in various neurologic disorders.

Estrogen ameliorates microglial activation by inhibiting the Kir2.1 inward-rectifier K(+) channel.

Microglial activation is implicated in the pathogenesis of Parkinson's disease (PD). Although the etiology of PD remains unclear, age and male gender are known PD risk factors. By comparing microglia and dopaminergic (DA) neurons in the substantia nigra (SN) of male and female mice of different ages, we found that the degrees of microglial activation and DA neuron loss increased with age in both genders, but were more pronounced in males, as were peripheral lipopolysaccharide (LPS)-induced microglial activation and DA neuron loss. A bilateral ovariectomy (OVX) eliminated the female-associated protection against age- and LPS-induced microglial activation, which suggests that ovary hormones are involved in gender-specific responses. Treating female mice with 17ß-estradiol supplements reduced the age-associated microglial activation in OVX mice. Moreover, pretreating mouse BV2 microglial cells with 17ß-estradiol inhibited LPS-induced elevation of Toll-like receptor 4, phosphorylated p38, and TNF-α levels. We then examined the effect of 17ß-estradiol on inward-rectifier K(+) channel Kir2.1, a known regulator of microglial activation. We found that 17ß-estradiol inhibited the Kir2.1 activity of BV2 cells by reducing the probability that the channel would be open. We conclude that age- and inflammation-associated microglial activation is attenuated by ovarian estrogen, because it inhibits Kir2.1.

[Diagnosis and treatment of isolated methylmalonic acidemia].

OBJECTIVE: To explore the clinical feature, therapeutic effect and prognosis of isolated methylmalonic acidemia. METHODS: The clinical characteristics, laboratory findings, treatment and outcome of 40 patients were retrospectively analyzed. The main treatment was a low-protein diet supplemented with L-carnitine and special milk free of leucine, valine, threonine and methionine. Vitamin B12 was also given to cobalamin responders. The patients were followed up every 1-3 months. RESULTS: Mutations in the MUT gene were identified in 30 of 33 patients who had accepted DNA testing. Thirty cases were treated and followed up regularly for from 1 month to 8 years. Eight cases had died, 8 had developed normal intelligence, among whom 4 from newborn screening were asymptomatic. Psychomotor developmental delay and mental retardation were present in 14 cases. The propionylcarnitine level, ratio of propionylcarnitine/acetylcarnitine in blood, methylmalonic acid and methylcitric acid levels in urine have decreased significantly, with the median values reduced respectively from 24.15 (7.92-81.02) µmol/L, 1.08 (0.38-6.01), 705.34 (113.79-3078.60) and 7.71 (0.52-128.21) to 10.50 (3.00-30.92) µmol/L, 0.63 (0.25-2.89), 166.23 (22.40-3322.21) and 3.96 (0.94-119.13) (P < 0.05). CONCLUSION: The prognosis of isolated methylmalonic acidemia may be predicted with the enzymatic subgroup, age at onset and cobalamin responsiveness. Outcome is unfavorable in neonatal patients and those who were non-responsive to cobalamin.

Pregabalin attenuates excitotoxicity in diabetes.

Diabetes can exacerbate seizures and worsen seizure-related brain damage. In the present study, we aimed to determine whether the standard antiepileptic drug pregabalin (PGB) protects against pilocarpine-induced seizures and excitotoxicity in diabetes. Adult male Sprague-Dawley rats were divided into either a streptozotocin (STZ)-induced diabetes group or a normal saline (NS) group. Both groups were further divided into subgroups that were treated intravenously with either PGB (15 mg/kg) or a vehicle; all groups were treated with subcutaneous pilocarpine (60 mg/kg) to induce seizures. To evaluate spontaneous recurrent seizures (SRS), PGB-pretreated rats were fed rat chow containing oral PGB (450 mg) for 28 consecutive days; vehicle-pretreated rats were fed regular chow. SRS frequency was monitored for 2 weeks from post-status epilepticus day 15. We evaluated both acute neuronal loss and chronic mossy fiber sprouting in the CA3 area. In addition, we performed patch clamp recordings to study evoked excitatory postsynaptic currents (eEPSCs) in hippocampal CA1 neurons for both vehicle-treated rats with SRS. Finally, we used an RNA interference knockdown method for Kir6.2 in a hippocampal cell line to evaluate PGB's effects in the presence of high-dose ATP. We found that compared to vehicle-treated rats, PGB-treated rats showed less severe acute seizure activity, reduced acute neuronal loss, and chronic mossy fiber sprouting. In the vehicle-treated STZ rats, eEPSC amplitude was significantly lower after PGB administration, but glibenclamide reversed this effect. The RNA interference study confirmed that PGB could counteract the ATP-sensitive potassium channel (KATP)-closing effect of high-dose ATP. By opening KATP, PGB protects against neuronal excitotoxicity, and is therefore a potential antiepileptogenic in diabetes. These findings might help develop a clinical algorithm for treating patients with epilepsy and comorbid metabolic disorders.

Effects of ketamine and its metabolites on ion currents in differentiated hippocampal H19-7 neuronal cells and in HEK293T cells transfected with α-hslo subunit.

Ketamine (KT), a dissociative anesthetic, is known to induce schizophrenia-like psychosis. The percentage of KT abuse has recently grown fast despite KT being a controlled drug. The mechanism of KT actions is related to the inhibition of NMDA receptors. Whether KT produces other effects on ion currents in hippocampal neurons remains unclear. In this study, we attempted to evaluate the possible effects of KT and other related compounds on ion currents in hippocampal neuron-derived H19-7 cells. This drug exerted an inhibitory effect on Ca(2+)-activated K(+) current (IK(Ca)) in these cells with an IC(50) value of 274 µM. Pimaric acid (30 µM) or abietic acid (30 µM), known to stimulate large-conductance Ca(2+)-activated K(+) channels, reversed KT-induced inhibition of I(K)(Ca). In HEK293T cells expressing a-humans low poke, KT-induced inhibition of I(K)(Ca) still existed. Dehydronorketamine (300 µM) had little or no effect on the IK(Ca) amplitude, while norketamine (300 µM) slightly but significantly suppressed it. In inside­out configuration, KT applied to the intracellular face of the membrane did not alter single channel conductance of large-conductance Ca(2+)-activated K(+) (BKCa) channels; however, it did significantly reduce the probability of channel openings. Addition of KT was effective in depressing the peak amplitude of voltage-gated Na(+) current. Moreover, the presence of KT was noted to enhance the amplitude of membrane electroporation-induced inward currents (IMEP) in differentiated H19-7 cells. KT-stimulated IMEP was reversed by further application of LaCl(3) (100 µM), but not by NMDA (30 µM). The modulations by this compound of ion channels may contribute to the underlying mechanisms through which KT and its metabolites influence the electrical behavior of hippocampal neurons if similar findings occur in vivo.

Evidence for inhibitory effects of flupirtine, a centrally acting analgesic, on delayed rectifier k(+) currents in motor neuron-like cells.

Flupirtine (Flu), a triaminopyridine derivative, is a centrally acting, non-opiate analgesic agent. In this study, effects of Flu on K(+) currents were explored in two types of motor neuron-like cells. Cell exposure to Flu decreased the amplitude of delayed rectifier K(+) current (I(K(DR))) with a concomitant raise in current inactivation in NSC-34 neuronal cells. The dissociation constant for Flu-mediated increase of I(K(DR)) inactivation rate was about 9.8 µM. Neither linopirdine (10 µM), NMDA (30 µM), nor gabazine (10 µM) reversed Flu-induced changes in I(K(DR)) inactivation. Addition of Flu shifted the inactivation curve of I(K(DR)) to a hyperpolarized potential. Cumulative inactivation for I(K(DR)) was elevated in the presence of this compound. Flu increased the amplitude of M-type K(+) current (I(K(M))) and produced a leftward shift in the activation curve of I(K(M)). In another neuronal cells (NG108-15), Flu reduced I(K(DR)) amplitude and enhanced the inactivation rate of I(K(DR)). The results suggest that Flu acts as an open-channel blocker of delayed-rectifier K(+) channels in motor neurons. Flu-induced block of I(K(DR)) is unlinked to binding to NMDA or GABA receptors and the effects of this agent on K(+) channels are not limited to its action on M-type K(+) channels.

Catheter ablation for paroxysmal and persistent atrial fibrillation.

BACKGROUND: Atrial fibrillation (AF) is the most common cardiac arrhythmia seen in cardiovascular departments. Treatments include medical interventions and catheter ablation. Due to uncertainties in medical therapies for AF, and the need to continue sinus rhythm, ablation has been recently considered as a viable alternative. Many new ablation methods based on pulmonary vein isolation (PVI) have been developed. OBJECTIVES: The primary objective of this review was to assess the beneficial and harmful effects of catheter ablation (CA) in comparison with medical treatment in patients with paroxysmal and persistent AF. The secondary objective was to determine the best regimen of CA. SEARCH METHODS: Searches were run on The Cochrane Central Register of Controlled Trials (CENTRAL) on The Cochrane Library Issue 3 2009, MEDLINE (1950 to August 2009), EMBASE (1980 to August 2009), the Chinese Biomedical Literature Database (1978 to August 2009) and the CKNI Chinese Paper Database (1994 to 2009) . Several journals published in Chinese were also handsearched. SELECTION CRITERIA: Randomised controlled trials (RCTs) in people with paroxysmal and persistent AF treated by any type of CA method. Two reviewers independently selected the trials for inclusion. DATA COLLECTION AND ANALYSIS: Assessments of risk of bias were performed by two reviewers, and relative risk (RR) and 95% confidence intervals (CI) were used for dichotomous variables. Meta-analysis were performed where appropriate. MAIN RESULTS: A total of 32 RCTs (3,560 patients) were included. RCTs were small in size and of poor quality.CA compared with medical therapies: seven RCTs indicated that CA had a better effect in inhibiting recurrence of AF [RR 0.27; 95% CI 0.18, 0.41)] but there was significant heterogeneity. There was limited evidence to suggest that sinus rhythm was restored during CA (one small trial: RR 0.28, 95% CI 0.20-0.40), and at the end of follow-up (RR 1.87, 95% CI 1.31-2.67; I(2)=83%). There were no differences in mortality (RR, 0.50, 95% CI 0.04 to 5.65), fatal and non-fatal embolic complication (RR 1.01, 95% CI 0.18 to 5.68) or death from thrombo-embolic events (RR 3.04, 95% CI 0.13 to 73.43).Comparisons of different CAs; 25 RCTs compared CA of various kinds. Circumferential pulmonary vein ablation was better than segmental pulmonary vein ablation in improving symptoms of AF (p<=0.01) and in reducing the recurrence of AF (p<0.01). There is limited evidence to suggest which ablation method was the best. AUTHORS' CONCLUSIONS: There is limited evidence to suggest that CA may be a better treatment option compared to medical therapies in the management of persistent AF. This review was also unable to recommend the best CA method.

Berberine activates Nrf2 nuclear translocation and protects against oxidative damage via a phosphatidylinositol 3-kinase/Akt-dependent mechanism in NSC34 motor neuron-like cells.

Berberine (BBR) is a well-known anti-diabetic herbal medicine in Asia due to its beneficial effects on insulin sensitivity, glucose metabolism and glycolysis. Here, we identified the critical role of phosphatidylinositol 3-kinase (PI3K)/Akt involved BBR cellular defense mechanisms and first revealed the novel effect of BBR on nuclear factor (erythroid-derived 2)-related factor-2 (Nrf2)/heme oxygenase (HO)-1 induction in NSC34 motor neuron-like cells. BBR (0.1-10 nM) led to increasing insulin receptor expression, Akt phosphorylation and enhanced oxidant-sensitive Nrf2/HO-1 induction, which were blocked by a PI3K inhibitor, LY294002. In H(2)O(2)-treated cells, BBR significantly attenuated ROS production and increased cell viability, antioxidant defense (GSH and SOD) and oxidant-sensitive proteins (HO-1 and Nrf2), which also were blocked by LY294002. Furthermore, BBR improved mitochondrial function by increasing mitochondrial membrane potential and decreasing the oxygen consumption rate. BBR-induced anti-apoptotic function was demonstrated by increasing anti-apoptotic protein Bcl-2 and survival of motor neuron protein (SMN) and by decreasing apoptotic proteins (cytochrome c, Bax and caspase). These results suggest that BBR, which is active at nanomolar concentration, is a potential neuroprotective agent via PI3K/Akt-dependent cytoprotective and antioxidant pathways.

Diazoxide reduces status epilepticus neuron damage in diabetes.

Diabetic hyperglycemia is associated with seizure severity and may aggravate brain damage after status epilepticus. Our earlier studies suggest the involvement of ATP-sensitive potassium channels (K(ATP)) in glucose-related neuroexcitability. We aimed to determine whether K(ATP) agonist protects against status epilepticus-induced brain damage. Adult male Sprague-Dawley rats were divided into two groups: the streptozotocin (STZ)-induced diabetes (STZ) group and the normal saline (NS) group. Both groups were treated with either diazoxide (15 mg/kg, i.v.) (STZ + DZX, NS + DZX) or vehicle (STZ + V, NS + V) before lithium-pilocarpine-induced status epilepticus. We evaluated seizure susceptibility, severity, and mortality. The rats underwent Morris water-maze tests and hippocampal histopathology analyses 24 h post-status epilepticus. A multi-electrode recording system was used to study field excitatory postsynaptic synaptic potentials (fEPSP). RNA interference (RNAi) to knockdown Kir 6.2 in a hippocampal cell line was used to evaluate the effect of diazoxide in the presence of high concentration of ATP. Seizures were less severe (P < 0.01), post-status epilepticus learning and memory were better (P < 0.05), and neuron loss in the hippocampal CA3 area was lower (P < 0.05) in the STZ + DZX than the STZ + V group. In contrast, seizure severity, post-status epilepticus learning and memory, and hippocampal CA3 neuron loss were comparable in the NS + DZX and NS + V groups. fEPSP was lower in the STZ + DZX but not in the NS + DZX group. The RNAi study confirmed that diazoxide, with its K(ATP)-opening effects, could counteract the K(ATP)-closing effect by high dose ATP. We conclude that, by opening K(ATP), diazoxide protects against status epilepticus-induced neuron damage during diabetic hyperglycemia.

Diosgenin, a plant-derived sapogenin, stimulates Ca2+-activated K+ current in human cortical HCN-1A neuronal cells.

The effects of diosgenin (3beta-hydroxy-5-spirostene), a plant-derived sapogenin, on ion currents in human cortical neurons (HCN-1A) were investigated. In the whole-cell configuration, diosgenin (0. -30 microM) increased the amplitude of K+ outward current (I(K)). Diosgenin-stimulated I(K) was sensitive to inhibition by paxilline (1 microM), but not by apamin (200 nM) or glibenclamide (10 muM). In the cell-attached configuration, diosgenin applied to the bath increased the activity of large-conductance Ca2+-activated K+ (BK(Ca)) channels without altering single-channel conductance. Diosgenin enhanced BK(Ca)-channel activity with an EC50 value of 25 microM. However, in inside-out patches, diosgenin applied to the intracellular surface had no effect on BK(Ca)-channel activity, while cilostazol or caffeic acid phenethyl ester increased it. As shown with the aid of intracellular Ca2+ measurements, diosgenin elevated intracellular Ca2+ in HCN-1A cells. Western blotting also revealed the presence of the alpha-subunit of BK (Ca) channels in these cells. The sustained stimulation of I(K) arises primarily from the diosgenin-induced Ca2+ influx across the cell membrane. The effect of diosgenin on these channels may affect the functional activity of cortical neurons. Abbreviations. I(K):K+ outward current I(K(Ca)):Ca2+-activated K+ current BK(Ca) channel:Large-conductance Ca2+-activated K+ channel CAPE:caffeic acid phenethyl ester [Ca2+] (i):intracellular Ca2+ concentration I/V relationship:current/voltage relationship K (ATP) channel:ATP-sensitive K+ channel K(Ca) channel:Ca2+-activated K+ channel.

Stimulatory actions of thymol, a natural product, on Ca(2+)-activated K(+) current in pituitary GH(3) cells.

Drugs that influence the opening of potassium (K(+)) channels and as a consequence cause hyperpolarization of cell membrane possess clinical potential. The large conductance Ca(2+)-activated K(+) (BK) channel is highly selective for K(+). Activation of this channel is Ca(2+)- and voltage-dependent. We have investigated the effects of thymol, a natural product, on ion currents in pituitary GH(3) cells. The patch-clamp technique was used to investigate the effect of thymol (100 microM) in these cells. Thymol reversibly stimulated the Ca(2+)-activated K(+) current with an EC (50) value of 75 microM. In a cell-attached configuration, application of thymol to the bath increased the activity of BK channels. BAPTA (1 mM) attenuated thymol-stimulated channel activity. In an experiment using the inside-out configuration, thymol exposed to the intracellular face of excised patches did not modify the single-channel conductance of these channels whereas it enhanced the channel activity. Neither menthol (100 microM) nor zingerone (100 microM) had an effect on BK-channel activity while AAPH (100 microM) suppressed it significantly. The stimulatory actions of thymol on Ca(2+)-activated K(+) currents may be associated with the underlying cellular mechanisms through which it affects neuronal or neuroendocrine functions.

The mechanism of inhibitory actions of S-petasin, a sesquiterpene of Petasites formosanus, on L-type calcium current in NG108-15 neuronal cells.

The effects of S-petasin, a sesquiterpene isolated from Petasites formosanus Kitamura, on ion currents in a mouse neuroblastoma and a rat glioma hybrid cell line, NG108-15, were examined with the aid of the whole-cell voltage-clamp technique. S-Petasin (1 - 300 microM) caused a decrease in the amplitude of L-type Ca2+ current (I(Ca,L)) in a concentration-dependent manner, however, it did not change the overall shape of the current-voltage relationship of I(Ca,L). The IC50 value for S-petasin-induced inhibition of I(Ca,L) was 11 microM. S-Petasin (10 microM) shifted the steady-state inactivation of I(Ca,L) to a more negative membrane potential by approximately -10 mV. S-petasin could prolong the recovery of I(Ca,L) inactivation. The inhibitory effect of S-petasin on I(Ca,L) was found to exhibit tonic and use-dependent characteristics. S-Petasin could inhibit I(Ca,L) evoked by action potential waveforms effectively. S-Petasin also suppressed low voltage-activated I(Ca,L) in NG108-15 cells. S-Petasin at a concentration of 100 microM had little effect on voltage-dependent Na+ current; however, it did produce an inhibitory effect on delayed rectifier K+ current in a time-dependent manner. These results demonstrate that S-petasin can interact directly with L-type Ca2+ channels in NG108-15 cells. These effects could contribute to the regulation of neuronal activity if similar results were found in neurons in vivo.