离子通道与肠易激综合征内脏高敏感的研究进展

肠易激综合征（IBS）是临床常见的功能性胃肠病之一,目前认为内脏高敏感是其重要的发病机制。近年,离子通道在内脏高敏感中的作用越来越受到重视。本文就离子通道在IBS内脏高敏感中的相关研究进展作一综述。     

Cardiovascular Ion Channels as a Molecular Target of Flavonoids

Flavonoids are a class of naturally occurring polyphenols abundant in edibles and beverages of plant origin. Epidemiological studies consistently associate high flavonoid intake with a reduced risk for the development of cardiovascular diseases. So far these beneficial effects have been mainly attributed to nonspecific antioxidant and antiinflammatory properties. However, there is an increasing body of evidence that flavonoids specifically target molecular structures including cardiovascular ion channels. Playing a pivotal role in the regulation of vascular tone and cardiac electric activity, ion channels represent a major target for the induction of antihypertensive and cardioprotective effects. Thus, pharmacological properties of flavonoids on cardiovascular ion channels, ion currents and tissue preparations are being increasingly addressed in experimental studies. Whereas it has become clear that cardiovascular ion channels represent an important molecular target of flavonoids, the published data have not yet been systematically reviewed.     

巨噬细胞调控离子通道致心律失常研究的最新进展

传统观点认为心律失常的发生机制主要与离子通道电流有关,近年来研究发现心脏中固有巨噬细胞和血液单核细胞分化而来的巨噬细胞,可通过调节ICa,T等离子通道影响离子电流,从而在心脏正常电传导中发挥作用,并与房性、室性心律失常密切相关.这为心律失常的治疗提供了新的思路.     

Ethanol Actions on Multiple Ion Channels: Which Are Important?

BACKGROUND: This review is based on a plenary lecture presented at the 1999 meeting of the Research Society on Alcoholism. It provides an overview of the search for sites of action for ethanol in the brain. Initial studies were directed at interaction of ethanol with membrane lipids, but during the past decade, emphasis has been shifted to protein sites, particularly those on ion channels. Molecular biological techniques have provided the opportunity to study isolated channels in cellular expression systems and also provide the opportunity to manipulate these channels in mutant mice. CONCLUSIONS: There is now compelling evidence that multiple ion channels are affected by ethanol and growing support for the idea that ethanol interacts directly with specific sites on ion channels. The key, and unanswered, question is which of these channels are responsible for alcohol-induced behaviors such as intoxication, tolerance, dependence, or craving. Mutant mice will likely give (some) answers to these questions during the next decade.     

Acute Effects of Ethanol on Recombinant Kainate Receptors: Lack of Role of Protein Phosphorylation

This study examined the acute actions of ethanol on recombinant rat GIuR6 kainate receptors expressed in Xenopus oocytes and HEK 293 cells. Electrophysiological recordings showed that co-application of ethanol with submaximal kainate concentrations resulted in similar inhibition of kainate-gated currents in both expression systems. Manipulation of intracellular phosphorylation pathways by intracellular dialysis with a solution without ATP and GTP did not modify the inhibitory effects of ethanol. Moreover, co-transfection of GIuR6 receptor subunits with PKA-α catalytic subunit or the calcium/ calmodulin-dependent protein kinase II (CamKII) catalytic fragment did not change the sensitivity of the receptor to ethanol. Treatment of Xenopus oocytes with specific inhibitors of PKC, PKA, CamKII, tyrosine kinases, and serine-threonine protein phosphatases did not affect the 100 mM ethanol-induced inhibition of GIuR6 receptor-mediated currents. Biochemical experiments with transiently transfected HEK 293 cells confirmed published reports that GIuR6 receptors are minimally phosphorylated under basal conditions in these cells and also revealed that acute ethanol did not increase GIuR6 phosphorylation. These results suggest that, under our experimental conditions, ethanol inhibits recombinant GIuR6 receptor function by a direct effect on the receptor rather than an indirect action via protein phosphorylation.     

Effects of Ethanol on NMDA Receptors in Brain: Possibilities for Mg2+ -Ethanol Interactions

The major excitatory neurotransmitter in the CNS is L-glutamate, and one of the subtypes of L-glutamate receptors, the N -methyl-D-aspartate (NMDA) subtype, has been found to be quite sensitive to inhibition by low concentrations of ethanol (5–50 mm). The NMDA receptor-ion channels are unique in that they exhibit a voltage-dependent blockade by physiological concentrations of Mg²⁺, a blockade that is relieved as the cell membrane is depolarized. Several lines of evidence also suggest that the activity of this receptor-channel complex may be regulated through a high-affinity Mg²⁺ site, which is distinct from the channel-blocking site and could even be located on the extracellular domain of the protein. This high-affinity Mg²⁺ site has been shown to increase the binding of N -[1-(2-thienyl) cyclohexyl]piperidine within the ion channel, as well as the binding of competitive antagonist such as 3-(±)-carboxypiperazine-4-yl)-[1,2]-propyl-1-phosphonic acid and the receptor coactivator glycine. The relationship between the acute effects of ethanol on receptor activation and the regulatory properties of Mg²⁺ is not yet known, although the hypomagnesemia that occurs in chronic alcoholism could certainly have implications for receptor function. A significant amount of molecular characterization of the multiple isoforms of the NMDA receptor-ion channel will be required before the role of Mg²⁺ can be clarified and any relationship between Mg²⁺ regulation and ethanol inhibition established.     

Structural Models of Ligand‐Gated Ion Channels: Sites of Action for Anesthetics and Ethanol

The molecular mechanism(s) of action of anesthetic, and especially, intoxicating doses of alcohol (ethanol [EtOH]) have been of interest even before the advent of the Research Society on Alcoholism. Recent physiological, genetic, and biochemical studies have pin‐pointed molecular targets for anesthetics and EtOH in the brain as ligand‐gated ion channel (LGIC) membrane proteins, especially the pentameric (5 subunit) Cys‐loop superfamily of neurotransmitter receptors including nicotinic acetylcholine (nAChRs), GABA_A (GABA_ARs), and glycine receptors (GlyRs). The ability to demonstrate molecular and structural elements of these proteins critical for the behavioral effects of these drugs on animals and humans provides convincing evidence for their role in the drugs' actions. Amino acid residues necessary for pharmacologically relevant allosteric modulation of LGIC function by anesthetics and EtOH have been identified in these channel proteins. Site‐directed mutagenesis revealed potential allosteric modulatory sites in both the trans‐membrane domain (TMD) and extracellular domain (ECD). Potential sites of action and binding have been deduced from homology modeling of other LGICs with structures known from crystallography and cryo‐electron microscopy studies. Direct information about ligand binding in the TMD has been obtained by photoaffinity labeling, especially in GABA_ARs. Recent structural information from crystallized procaryotic (ELIC and GLIC) and eukaryotic (GluCl) LGICs allows refinement of the structural models including evaluation of possible sites of EtOH action.     

转运通路——疟疾治疗药物新靶点

处于红内期的疟原虫为摄取营养，在红细胞产生新的转运通路。由于其转运通路具有一系列生物学特性，故既可以作为直接的药物靶点，也可以作为药物寻靶途径间接引导细胞毒药物到达细胞内的作用位点，发挥抗疟作用。研究并应用该运转通路是抗疟药的研究方向之一。     

Neuroscience Research: How Has It Contributed to Our Understanding of Alcohol Abuse and Alcoholism? A Review

Alcohol abuse and alcoholism are the greatest substance abuse problems in the United States today and contribute to numerous medical and social problems. To deal with many of these problems, an understanding of how alcohol acts on the brain is extremely important. Advances in neuroscience research have provided significant clues about where and how alcohol works on the brain. Alcohol clearly acts on membrane function, altering such processes as ion movements and neurotransmitter interactions with their receptors. Although these alcohol-induced alterations are presumed to relate to changes in behavior, this has not been clearly established. However, alcohol research is on the threshold of making a giant leap forward in our understanding the etiology of alcoholism.     

Effects of acamprosate on neuronal receptors and ion channels expressed in Xenopus oocytes

Background: Acamprosate (calcium acetylhomotaurinate) has proven to be a moderately effective pharmacological adjunct for the treatment of alcoholism. However, the central nervous system mechanism by which acamprosate reduces alcohol relapse remains unclear. Here we survey a number of metabotropic receptors, ligand‐gated ion channels, and voltage‐gated ion channels, to determine if acamprosate has actions at these sites in the central nervous system. Methods: Xenopus oocytes were injected with cDNAs or cRNAs encoding metabotropic glutamate receptors 1 and 5, M1 muscarinic receptors, glycine α1 homomeric and α1β1 heteromeric receptors, γ‐aminobutyric acid A (GABA_Aα4β3δ, α4β3γ2s, and α1β2γ2s) receptors, vanilloid receptor 1, and various combinations of α and β subunits of voltage‐gated Na⁺ channels. Electrophysiological responses were measured using two‐electrode voltage clamp parameters after activation with agonists or voltage steps (for the voltage‐gated channels). Acamprosate (0.1 to 100 μM) was pre‐applied for 1 minute, followed by co‐application with agonist. Acamprosate was also applied with ethanol to determine if it altered ethanol responses at some of these receptors and channels. Results: None of the receptors or ion channels responded to acamprosate alone. Acamprosate also failed to alter the activation of receptors or channels by agonists or after activation of voltage‐gated channels. There was no effect of acamprosate on ethanol responses at GABA_Aα1β2γ2s receptors or Na⁺ channels. Conclusions: Acamprosate does not significantly modulate the function of these receptors and ion channels at clinically relevant concentrations. Thus, the clinical effectiveness of acamprosate in the treatment of alcoholism is not likely due to direct effects on these receptors or ion channels.     

Acute stress enhances glutamatergic transmission in prefrontal cortex and facilitates working memory

The prefrontal cortex (PFC), a key brain region controlling cognition and emotion, is strongly influenced by stress. While chronic stress often produces detrimental effects on these measures, acute stress has been shown to enhance learning and memory, predominantly through the action of corticosteroid stress hormones. We used a combination of electrophysiological, biochemical, and behavioral approaches in an effort to identify the cellular targets of acute stress. We found that behavioral stressors in vivo cause a long-lasting potentiation of NMDAR- and AMPAR-mediated synaptic currents via glucocorticoid receptors (GRs) selectively in PFC pyramidal neurons. This effect is accompanied by increased surface expression of NMDAR and AMPAR subunits in acutely stressed animals. Furthermore, behavioral tests indicate that working memory, a key function relying on recurrent excitation within networks of PFC neurons, is enhanced by acute stress via a GR-dependent mechanism. These results have identified a form of long-term potentiation of synaptic transmission induced by natural stimuli in vivo, providing a potential molecular and cellular mechanism for the beneficial effects of acute stress on cognitive processes subserved by PFC.     

Antiglutamatergic strategies for ethanol detoxification: comparison with placebo and diazepam

BACKGROUND: Benzodiazepines are the standard pharmacotherapies for ethanol detoxification, but concerns about their abuse potential and negative effects upon the transition to alcohol abstinence drive the search for new treatments. Glutamatergic activation and glutamate receptor up-regulation contribute to ethanol dependence and withdrawal. This study compared 3 antiglutamatergic strategies for ethanol detoxification with placebo and to the benzodiazepine, diazepam: the glutamate release inhibitor, lamotrigine; the N-methyl-D-aspartate glutamate receptor antagonist, memantine; and the AMPA/kainite receptor inhibitor, topiramate. METHODS: This placebo-controlled randomized single-blinded psychopharmacology trial studied male alcohol-dependent inpatients (n=127) with clinically significant alcohol withdrawal symptoms. Subjects were assigned to 1 of 5 treatments for 7 days: placebo, diazepam 10 mg TID, lamotrigine 25 mg QID, memantine 10 mg TID, or topiramate 25 mg QID. Additional diazepam was administered when the assigned medication failed to suppress withdrawal symptoms adequately. RESULTS: All active medications significantly reduced observer-rated and self-rated withdrawal severity, dysphoric mood, and supplementary diazepam administration compared with placebo. The active medications did not differ from diazepam. CONCLUSIONS: This study provides the first systematic clinical evidence supporting the efficacy of a number of antiglutamatergic approaches for treating alcohol withdrawal symptoms. These data support the hypothesis that glutamatergic activation contributes to human alcohol withdrawal. Definitive studies of each of these medications are now needed to further evaluate their effectiveness in treating alcohol withdrawal.     

Regulatory role of excitatory amino acids in reproduction

Glutamate, the major excitatory amino acid (EAA) transmitter in the central nervous system, has been implicated as a critical mediator in brain function. Glutamate and its receptors are found in all key hypothalamic areas critically involved in reproduction. Administration of glutamate and its agonists can bring about LH release in animals with a steroid background. Antagonists of the ionotropic glutamate receptors inhibited LH release and abolished the steroid-induced and the preovulatory LH surge. Both NMDA and non-NMDA receptor antagonists can also inhibit pulsatile LH release in castrated animals. The preoptic area has been implicated as a primary site of action of NMDA, while non-NMDA agonists have been suggested to act primarily at the arcuate/median eminence level. While EAAs may act directly on GnRH neurons to enhance GnRH release, the majority of evidence suggests that an indirect mechanism, involving EAA activation of nitric oxide and/or catecholamines, plays a major role in the GnRH-releasing effects of EAAs. Furthermore, there is also some evidence that the tonic inhibitory effect of opioids on GnRH may also involve, at least in part, a suppression of glutamate. Finally, EAA stimulation of GnRH/LH release is markedly attenuated in middle-aged rats, suggesting that a defect in glutamate neurotransmission may underlie the attenuated LH surge observed in aging.     

Ethanol Inhibition of AMPA and Kainate Receptor-Mediated Depolarizations of Hippocampal Area CA1

Longitudinal hippocampal slices were prepared from adult female rats. The excitatory amino acids, α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and kainic acid, were applied to area CA1, and the resulting depolarizations were measured using the grease-gap electrophysiological technique. Agonist dose-response curves were generated in the presence and absence of various concentrations of ethanol. Ethanol (25–200 mM) significantly attenuated the depolarizations that were produced by each agonist. In addition, we found that ethanol potently antagonized kainate-induced depolarizations across the agonist concentration-response curve, whereas it significantly suppressed only AMPA responses that were induced with moderate-to-high agonist concentrations.
These results indicate that ethanol has potent antagonist actions against non- N -methyl- d -aspartate (NMDA) excitatory amino acid-induced neuronal depolarizations in hippocampal area CA1. Moreover, the relative potency of ethanol depends on the specific excitatory agonist tested and the concentration of that agonist. This suggests that, in addition to the known effects of ethanol on NMDA receptor-mediated activity, it may also potently attenuate ongoing "fast" glutamatergic synaptic activity in the hippocampus.     

Role of major NMDA or AMPA receptor subunits in MK-801 potentiation of ethanol intoxication

Background: The glutamate system plays a major role in mediating EtOH’s effects on brain and behavior, and is implicated in the pathophysiology of alcohol‐related disorders. N‐methyl‐D‐aspartate receptor (NMDAR) antagonists such as MK‐801 (dizocilpine) interact with EtOH at the behavioral level, but the molecular basis of this interaction is unclear. Methods: We first characterized the effects of MK‐801 treatment on responses to the ataxic (accelerating rotarod), hypothermic and sedative/hypnotic effects of acute EtOH administration in C57BL/6J and 129/SvImJ inbred mice. Effects of another NMDAR antagonist, phencyclidine, on EtOH‐induced sedation/hypnosis were also assessed. Gene knockout of the NMDAR subunit NR2A or l ‐alpha‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate GluR1 or pharmacological antagonism of the NMDAR subunit NR2B (via Ro 25‐6981) was employed to examine whether inactivating any one of these glutamate signaling molecules modified MK‐801’s effect on EtOH‐related behaviors. Results: MK‐801 markedly potentiated the ataxic effects of 1.75 g/kg EtOH and the sedative/hypnotic effects of 3.0 g/kg EtOH, but not the hypothermic effects of 3.0 g/kg EtOH, in C57BL/6J and 129/SvImJ mice. Phencyclidine potentiated EtOH‐induced sedation/hypnosis in both inbred strains. Neither NR2A nor GluR1 KO significantly altered basal EtOH‐induced ataxia, hypothermia, or sedation/hypnosis. Ro 25‐6981 modestly increased EtOH‐induced sedation/hypnosis. The ability of MK‐801 to potentiate EtOH‐induced ataxia and sedation/hypnosis was unaffected by GluR1 KO or NR2B antagonism. NR2A KO partially reduced MK‐801 + EtOH‐induced sedation/hypnosis, but not ataxia or hypothermia. Conclusions: Data confirm a robust and response‐specific potentiating effect of MK‐801 on sensitivity to EtOH’s intoxicating effects. Inactivation of three major components of glutamate signaling had no or only partial impact on the ability of MK‐801 to potentiate behavioral sensitivity to EtOH. Further work to elucidate the mechanisms underlying NMDAR × EtOH interactions could ultimately provide novel insight into the role of NMDARs in alcoholism and its treatment.     

KB130015, A New Amiodarone Derivative with Multiple Effects on Cardiac Ion Channels

KB130015 (KB015), a new drug structurally related to amiodarone, has been proposed to have antiarrhythmic properties. In contrast to amiodarone, KB015 markedly slows the kinetics of inactivation of Na⁺ channels by enhancing concentration‐dependently (K_0.5# 2 μM) a slow‐inactivating I_Na component (#_slow# 50 ms) at the expense of the normal, fast‐inactivating component (#_fast# 2 to 3 ms). However, like amiodarone, KB015 slows the recovery from inactivation and causes a shift (K_0.5. # 6.9 μM) of the steady‐state voltage‐dependent inactivation to more negative potentials. Despite prolonging the opening of Na⁺ channels KB015 does not lengthen but often shortens the action potential duration (APD) in pig myocytes or in multicellular preparations. Only short APDs in mouse are markedly prolonged by KB015, which frequently induces early afterdepolarizations. KB015 has also an effect on other ion channels. It decreases the amplitude of the L‐type Ca²⁺ current (I^Ca‐L) without changing its time course, and it inhibits G‐protein gated and ATP‐gated K⁺ channels. Both the receptor‐activated I^k(ACH) (induced in atrial myocytes by either ACh, adenosine or sphingosylphosphorylcholine) and the receptor‐independent (GTPγS‐induced or background) I^k(ACH) are concentration‐dependently (K_0.5# 0.6 – 0.9 μM) inhibited by KB015. I^k(ATP), induced in atrial myocytes during metabolic inhibition with 2,4‐dinitrophenol (DNP), is equally suppressed. However, KB015 has no effect on I_K1 or on I_to. Consistent with the effects in K⁺ currents, KB015 does not depolarize the resting potential but antagonizes the APD shortening by muscarinic receptor activation or by DNP. Intracellular cell dialysis with KB015 has marginal or no effect on Na⁺ or K⁺ channels and does not prevent the effect of extracellularly applied drug, suggesting that KB015 interacts directly with channels at sites more easily accessible from the extracellular than the intracellular side of the membrane. At high concentrations KB015 exerts a positive inotropic action. It also interacts with thyroid hormone nuclear receptors. Its toxic effects remain largely unexplored, but it is well tolerated during chronic administration.     

Effects of Chronic Ethanol Exposure on Oxidation and NMDA-Stimulated Neuronal Death in Primary Cortical Neuronal Cultures

Excessive oxidative radical formation has been implicated in a number of neurodegenerative processes, including glirtamate-N-methylo-aspartate (NMDA)-mediated excitotoxicity. Previous studies have suggested that the formation of reactive oxygen species (ROS) during NMDA exposure is involved in triggering the excitotoxic cascade. Chronic exposure of primary neuronal cultures to ethanol has been shown to potentiate NMDA-mediated processes, such as nitric oxide formation and excitotoxicity. It was the objective of this study to investigate the role of NMDA and ROS formation in the development of NMDA supersensitivity after chronic ethanol exposure. The fluorescent dyes dichlorofluorescein diacetate (H₂DCF) and propidium iodide, which have been shown to be reliable markers for the detection of cellular oxidation and cell death, respectively, in neuronal culture preparations, were used to examine the relationship between ROS production and NMDA-mediated neuronal death after chronic ethanol administration. Cultures treated chronically with ethanol (100 mM) for 96 hr displayed significantly less H₂DCF oxidation when exposed to various concentrations of FeSO₄ for 25 min. However, this decrease in intracellular oxidation did not have any apparent inhibitory effects on the amount of cell death observed 12 hr after the 25-min exposure to FeSO₄. When NMDA-FeSO₄-mediated oxidation was examined in cultures treated chronically with ethanol, dose-dependent increases in H₂DCF oxidation were observed, but only in control-treated cultures. This blunting of intracellular H₂DCF oxidation did not attenuate the potentiation of NMDA-mediated excitotoxicity observed after chronic ethanol exposure. These results suggest that the observed supersensitivity to NMDA is not due to increases in intracellular ROS formation and that chronic ethanol may induce neuronal factors that reduce ROS formation, but do not protect against normal death.