Effect of a neuronal sodium channel blocker on magnetic resonance derived indices of brain water content during global cerebral ischemia

Diffusion-weighted magnetic resonance imaging (DWI) with calculation of the apparent diffusion coefficient (ADC) of water is a widely used noninvasive method to measure movement of water from the extracellular to the intracellular compartment during cerebral ischemia. Lamotrigine, a neuronal Na(+) channel blocker, has been shown to attenuate the increase in extracellular concentrations of excitatory amino acids (EAA) during ischemia and to improve neurological and histological outcome. Because of its proven ability to reduce EAA levels during ischemia, lamotrigine should also minimize excitotoxic-induced increases in intracellular water content and therefore attenuate changes in the ADC. In this study, we sought to determine the effect of lamotrigine on intra- and extracellular water shifts during transient global cerebral ischemia. Fifteen New Zealand white rabbits were anesthetized and randomized to one of three groups: a control group, a lamotrigine-treated group, or a sham group. After being positioned in the bore of the magnet, a 12-min 50-s period of global cerebral ischemia was induced by inflating a neck tourniquet. During ischemia and early reperfusion there was a similar and significant decrease of the ADC in both the lamotrigine and control group. The ADC in the sham ischemia group remained at baseline throughout the experiment. Lamotrigine-mediated blockade of voltage-gated sodium channels did not prevent the intracellular movement of water during 12 min 50 s of global ischemia, as measured by the ADC, suggesting that the ADC decline may not be mediated by voltage-gated sodium influx and glutamate release.     

A possible role for nerve growth factor in the augmentation of sodium channels in models of chronic pain

Inflammation induces an upregulation of sodium channels in sensory neurons. This most likely occurs as a result of the retrograde transport of cytochemical mediators released during the inflammatory response. The purpose of this study was to determine the effect of the subcutaneous administration of one such mediator, nerve growth factor (NGF), on the production of sodium channels in neurons of the rat dorsal root ganglion. For this, hindpaw withdrawal from either a thermal or mechanical stimulus was measured in rats at selected intervals for up to 2 weeks following injections of NGF. Sodium channel augmentation was then examined in dorsal root ganglia using site-specific, anti-sodium channel antibodies. Both thermal and mechanical allodynia was observed between 3 and 12 h post-injection. The hyperalgesic response returned to baseline by approximately 24 h post-injection. Sodium channel labeling was found to increase dramatically in the small neurons of the associated dorsal root ganglia beginning at 23 h, reached maximum intensity by 1 week, and persisted for up to 3 months post-injection. Pre-blocking NGF with anti-NGF prevented the NGF-induced decrease in paw withdrawal latencies and significantly reduced the intensity of sodium channel labeling. The results indicate that NGF is an important mediator both in the development of acute hyperalgesia and in the stimulation of sodium channel production in dorsal root ganglia during inflammation.     

Simultaneous action of MK-801 (dizclopine) on dopamine, glutamate, aspartate and GABA release from striatum isolated nerve endings

The simultaneous effect of MK-801 on the baseline- and depolarization (20 microM veratridine or 30 mM high K+)-evoked release of endogenous dopamine, glutamate (Glu), aspartate (Asp), and GABA is investigated in the same preparation of rat striatum isolated nerve endings. MK-801, in the microM range, selectively increases the baseline and high K+ depolarization-evoked release of dopamine, without causing any effect on the baseline or on the high K+-evoked release of Glu, Asp and GABA. In addition to this selective action on dopamine release, MK-801 inhibits the veratridine depolarization-evoked release of all the neurotransmitters tested, including dopamine. In SBFI and fura-2 preloaded striatal synaptosomes, MK-801 inhibits the elevation of internal Na+ (Na(i)) and the elevation of internal Ca2+ (Ca(i)) induced by veratridine depolarization. The elevation of Ca(i) induced by high K+ depolarization is unchanged by MK-801. This study reveals two separate MK-801 actions. (1) The voltage-independent action, which increases dopamine release selectively, and might contribute to the effects of MK-801 on motor coordination. (2) The voltage-dependent action, which inhibits all the veratridine-evoked responses including the evoked release of the excitatory amino acids (which are particularly concentrated in striatum nerve endings), and might contribute to the anticonvulsant and neuroprotective effects of MK-801.     

Delayed Administration of the K+ Channel Activator Cromakalim Attenuates Cerebral Vasospasm after Experimental Subarachnoid Hemorrhage

Summary ? Background. Delayed cerebral vasospasm remains an unpredictable and inadequately treated complication of aneurysmal subarachnoid hemorrhage (SAH). Recent evidence indicates that the potassium channel activator cromakalim is capable of limiting cerebral vasospasm in rabbits when administered immediately after experimental SAH (i.e. before spastic constriction has been initiated). However, the ultimate clinical value of cromakalim for treating vasospasm will depend in part on its effectiveness when administered after SAH-induced constriction has already been initiated. The present study examined the effects of cromakalim on vasospasm when treatment was initiated after SAH-induced constriction was underway.  Methods. New Zealand white rabbits were subjected to experimental SAH by injecting autologous blood into the cisterna magna. Cromakalim (0.03, 0.1 or 0.3 mg/kg) or vehicle was injected intravenously at 8 hour intervals beginning 24 hours post-SAH. Animals were killed by perfusion fixation 48 hours after SAH. Basilar arteries were removed and sectioned, and cross-sectional area was measured.  Findings. The average cross sectional areas of basilar arteries were reduced by 64% and 68% in the SAH-only and SAH+vehicle groups, respectively. Treatment with cromakalim dose-dependently attenuated SAH-induced constriction. The groups treated with 0.03, 0.1, and 0.3 mg/kg cromakalim exhibited average decreases in cross-sectional area of 57%, 42%, and 19%, respectively.  Interpretation. These findings indicate that cromakalim dose-dependently attenuates cerebral vasospasm when administered 24 hours after experimental SAH in the rabbit. The results suggest K_ATP channel activators, such as cromakalim, could be of benefit for reversing cerebral vasospasm after aneurysmal SAH.     

Subcellular compartmentalization of a potassium channel (Kv1.4): preferential distribution in dendrites and dendritic spines of neurons in the dorsal cochlear nucleus

Voltage-dependent ion channels have specific patterns of distribution along the neuronal plasma membrane of dendrites, cell bodies and axons, which need to be unravelled in order to understand their contribution to neuronal excitability and firing patterns. We have investigated the subcellular compartmentalization of Kv1.4, a transient, fast-inactivating potassium channel, in fusiform cells and related interneurons of the rat dorsal cochlear nucleus. A polyclonal antibody which binds to a region near the N-terminus domain of a Kv1.4 channel was raised in rabbits. Using a high-resolution combination of immunocytochemical methods, Kv1.4 was localized mainly in the apical dendritic trunks and cell bodies of fusiform cells, as well as in dendrites and cell bodies of interneurons of the dorsal cochlear nucleus, likely cartwheel cells. Quantitative immunogold immunocytochemistry revealed a pronounced distal to proximal gradient in the dendrosomatic distribution of Kv1. 4. In plasma membrane localizations, Kv1.4 was preferentially present in dendritic spines, either in the spine neck or in perisynaptic locations, always away from the postsynaptic density. These findings indicate that Kv1.4 is largely distributed in dendritic compartments of fusiform and cartwheel cells of the dorsal cochlear nucleus. Its preferential localization in dendritic spines, where granule cell axons make powerful excitatory synapses, suggests a role for this voltage-dependent ion channel in the regulation of dendritic excitability and excitatory inputs.     

(S)-(—)-氨氯地平苯磺酸盐二水合物的制备

氨氯地平消旋体经D-(—)-酒石酸拆分,得到(S)-(—)-氨氯地平,再与苯磺酸成盐制得钙通道阻滞剂(S)-(—)-氨氯地平苯磺酸盐二水合物,收率67%,光学纯度近100%.     

Cardiovascular Medication Use and Risk of Acute Exacerbation in Patients With Asthma-COPD Overlap (CVACO Study)

PurposeCurrent clinical guidelines are unclear regarding the association of cardiovascular medication with the risk of acute exacerbation (AE) in patients with asthma-chronic obstructive pulmonary disease (COPD) overlap (ACO).MethodsWe conducted a retrospective cohort study by interrogating the claims database of Taipei Veterans General Hospital. Patients with coexistent fixed airflow limitation and asthma were enrolled as an ACO cohort between 2009 and 2017. Exposure to cardiovascular medications, including angiotensin converting enzyme inhibitors (ACEIs), angiotensin II receptor blockers (ARBs), non-selective beta-blockers, cardioselective beta-blockers, dihydropyridine (DHP) calcium channel blockers (CCBs), and non-DHP CCBs, in 3-month period each served as time-dependent covariates. Patients receiving a cardiovascular medication ≥ 28 cumulative daily doses were defined as respective cardiovascular medication users. Patients were followed up until December 31, 2018. The primary endpoint was severe AE, defined as hospitalization or emergency department visit for either asthma, COPD, or respiratory failure. The secondary outcome was moderate AE.ResultsThe final study cohort consisted of 582 ACO subjects, with a mean follow-up period of 2.98 years. After adjustment, ARB (hazard ratio [HR], 0.64, 95% confidence interval [CI], 0.44–0.93, P = 0.019), cardioselective beta-blocker (HR, 0.29, 95% CI, 0.11–0.72, P = 0.008) and DHP CCB (HR, 0.66, 95% CI, 0.45–0.97, P = 0.035) therapies were associated with lower risks of severe AE. ARB (HR, 0.42, 95% CI, 0.30–0.62, P < 0.001) and DHP CCB (HR, 0.55, 95% CI, 0.38–0.80, P = 0.002) therapies were associated with lower risks of moderate AE. Cardioselective beta-blockers, ARBs, and DHP CCBs were associated with lower risks of severe AE in frequent exacerbators. ACEI, non-selective beta-blocker, or non-DHP CCB use did not change the risk of severe AE.ConclusionsARB, cardioselective beta-blocker, and DHP CCB therapies may lower the risk of AE in patients with ACO.     

Niflumic acid inhibits chloride conductance of rat skeletal muscle by directly inhibiting the CLC-1 channel and by increasing intracellular calcium

BACKGROUND AND PURPOSE: Given the crucial role of the skeletal muscle chloride conductance (gCl), supported by the voltage-gated chloride channel CLC-1, in controlling muscle excitability, the availability of ligands modulating CLC-1 are of potential medical as well as toxicological importance. Here, we focused our attention on niflumic acid (NFA), a molecule belonging to the fenamates group of non-steroidal anti-inflammatory drugs (NSAID). EXPERIMENTAL APPROACH: Rat muscle Cl(-) conductance (gCl) and heterologously expressed CLC-1 currents were evaluated by means of current-clamp (using two-microelectrodes) and patch-clamp techniques, respectively. Fura-2 fluorescence was used to determine intracellular calcium concentration, [Ca(2+)](i), in native muscle fibres. KEY RESULTS: NFA inhibited native gCl with an IC(50) of 42 muM and blocked CLC-1 by interacting with an intracellular binding site. Additionally, NFA increased basal [Ca(2+)](i) in myofibres by promoting a mitochondrial calcium efflux that was not dependent on cyclooxygenase or CLC-1. A structure-activity study revealed that the molecular conditions that mediate the two effects are different. Pretreatment with the Ca-dependent protein kinase C (PKC) inhibitor chelerythrine partially inhibited the NFA effect. Therefore, in addition to direct channel block, NFA also inhibits gCl indirectly by promoting PKC activation. CONCLUSIONS AND IMPLICATIONS: These cellular effects of NFA on skeletal muscle demonstrate that it is possible to modify CLC-1 and consequently gCl directly by interacting with channel proteins and indirectly by interfering with the calcium-dependent regulation of the channel. The effect of NFA on mitochondrial calcium stores suggests that NSAIDs, widely used drugs, could have potentially dangerous side-effects.     

Congenital hyperinsulinism: Global and Japanese perspectives

Over the past 20 years, there has been remarkable progress in the diagnosis and treatment of congenital hyperinsulinism (CHI). These advances have been supported by the understanding of the molecular mechanism and the development of diagnostic modalities to identify the focal form of ATP‐sensitive potassium channel CHI. Many patients with diazoxide‐unresponsive focal CHI have been cured by partial pancreatectomy without developing postsurgical diabetes mellitus. Important novel findings on the genetic basis of the other forms of CHI have also been obtained, and several novel medical treatments have been explored. However, the management of patients with CHI is still far from ideal. First, state‐of‐the‐art treatment is not widely available worldwide. Second, it appears that the management strategy needs to be adjusted according to the patient's ethnic group. Third, optimal management of patients with the diazoxide‐unresponsive, diffuse form of CHI is still insufficient and requires further improvement. In this review, we describe the current landscape of this disorder, discuss the racial disparity of CHI using Japanese patients as an example, and briefly note unanswered questions and unmet needs that should be addressed in the near future.     

Structure and function of delta-atracotoxins: lethal neurotoxins targeting the voltage-gated sodium channel.

Delta-atracotoxins (delta-ACTX), isolated from the venom of Australian funnel-web spiders, are responsible for the potentially lethal envenomation syndrome seen following funnel-web spider envenomation. They are 42-residue polypeptides with four disulfides and an "inhibitor cystine-knot" motif with structural but not sequence homology to a variety of other spider and marine snail toxins. Delta-atracotoxins induce spontaneous repetitive firing and prolongation of action potentials resulting in neurotransmitter release from somatic and autonomic nerve endings. This results from a slowing of voltage-gated sodium channel inactivation and a hyperpolarizing shift of the voltage-dependence of activation. This action is due to voltage-dependent binding to neurotoxin receptor site-3 in a similar, but not identical, fashion to scorpion alpha-toxins and sea anemone toxins. Unlike other site-3 neurotoxins, however, delta-ACTX bind with high affinity to both cockroach and mammalian sodium channels but low affinity to locust sodium channels. At present the pharmacophore of delta-ACTX is unknown but is believed to involve a number of basic residues distributed in a topologically similar manner to scorpion alpha-toxins and sea anemone toxins despite distinctly different protein scaffolds. As such, delta-ACTX provide us with specific tools with which to study sodium channel structure and function and determinants for phyla- and tissue-specific actions of neurotoxins interacting with site-3.