Calcium Signaling Is Involved in EthanolInduced Volume Decrease and Gap Junction Closure in Cultured Rat Gastric Mucosal Cells

Cortical control of striatal fast-spiking interneuron synchrony

KEY POINTS

Electrical synapses between striatal fast-spiking interneurons in adult mice occur in ∼8% of assayed pairs. Coincident, convergent cortical input onto fast-spiking interneurons significantly contributes to fast-spiking interneuron synchrony Electrical synapses between fast-spiking interneurons provide only minor enhancement of fast-spiking interneuron synchrony. These results suggest a mechanism by which adult mouse fast-spiking interneurons of the striatum synchronize in the face of declining expression of the electrical synapse-forming connexin-36 protein.

ABSTRACT

Inhibitory fast-spiking interneurons in the dorsal striatum regulate actions and action strategies, including habits. Fast-spiking interneurons are widely believed to synchronize their firing due to the electrical synapses formed between these neurons. However, neuronal modeling data suggest convergent cortical input may also drive synchrony in fast-spiking interneuron networks. To better understand how fast-spiking interneuron synchrony arises, we performed dual whole-cell patch clamp electrophysiology experiments to inform a simple Bayesian network modeling cortico-fast-spiking interneuron circuitry. Dual whole-cell patch clamp electrophysiology revealed that while responsivity to corticostriatal input activation was high in fast-spiking interneurons, few of these neurons exhibited electrical coupling in adult mice. In simulations of a cortico-fast-spiking interneuron network informed by these data, the degree of glutamatergic cortical convergence onto fast-spiking interneurons significantly increased fast-spiking interneuron synchronization while manipulations of electrical coupling between these neurons exerted relatively little impact. These results suggest that the primary source of functional coordination of fast-spiking interneuron activity in adulthood arises from convergent corticostriatal input activation. Abstract figure legend Dual whole-cell patch clamp recordings of dorsal striatal fast-spiking interneurons (FSIs; red circles) rarely (8 percentage) form electrical synapses with other FSIs in adult mouse. In a two-layer in silico model of cortical pyramidal neuron (gray triangles) input to FSIs using empirically defined cortico-FSI synaptic weights, synchronous FSI-FSI activity (in the absence of abundant electrical synapses) is achievable by convergent cortical pyramidal excitation of FSIs. This article is protected by copyright. All rights reserved.

Brain circuits and neurochemical systems in essential tremor: insights into current and future pharmacotherapeutic approaches

INTRODUCTION

There are few medications that are available for the treatment of essential tremor (ET) and they are only moderately effective. Areas covered: Data were obtained from a PubMed search. Original articles, review articles, and clinical guidelines were included. Two disease models for ET have been proposed: 1) the olivary model, which attributes ET to a pathological pacemaker in the inferior olivary nucleus, and 2) the cerebellar degeneration model, which postulates that ET originates in the cerebellum and could be related to deficient or abnormal Purkinje cell (PC) output. Underlying biochemical dysfunction in T-type calcium channels (T-tCaC) may loosely be linked to the first model and deficiency/abnormality in γ-aminobutyric acid (GABA) neurotransmission, to the second. Expert commentary: Human data points robustly to the role of GABA in ET. Numerous medications that target the GABA system have been tried, with variable success. Given the many different types of GABA-ergic neurons, and the multitude of GABA_A receptor subtypes, a given medication could have competing/cancelling effects. It would seem that influencing GABA receptors broadly is not as effective as targeting certain GABA_A receptor subtypes. Future research should seek to identify molecular candidates that have a more targeted effect within the GABA system.

Essential Tremor: What We Can Learn from Current Pharmacotherapy

BACKGROUND

The pathophysiology of essential tremor, especially at the cellular level, is poorly understood. Although no drug has been specifically designed to treat essential tremor, several medications improve tremor, and others worsen it. Studying the mechanism of actions of these medications can help our understanding of tremor pathophysiology and contribute to future rational drug design.

METHODS

We reviewed literature, concentrating on mechanisms of action, of various medications that mitigate tremor.

RESULTS

Many medications have multiple mechanisms of actions, making simple correlations difficult. Medications that increase the duration of opening of gamma-aminobutyric acid (GABA)-A receptors are most consistently associated with tremor improvement. Interestingly, drugs that increase GABA availability have not been associated with improved tremor. Other mechanisms possibly associated with tremor improvement include antagonism of alpha-2 delta subunits associated with calcium channels, inhibition of carbonic anhydrase, and inhibition of the synaptic vesicle protein 2A. Drugs that block voltage-gaited sodium channels do not affect tremor. The ideal beta-adrenergic blocker requires B2 affinity (non-cardiac selective), has no sympathomimetic properties, does not require membrane stabilization properties, and may benefit from good central nervous system penetration.

DISCUSSION

To date, serendipitous observations have provided most of our understanding of tremor cellular physiology. Based on similarities to currently effective drugs or rational approximations and inferences, several currently available agents should be considered for tremor trials.

Ca2+-induced uncoupling of Aplysia bag cell neurons

Electrical transmission is a dynamically regulated form of communication and key to synchronizing neuronal activity. The bag cell neurons of Aplysia are a group of electrically coupled neuroendocrine cells that initiate ovulation by secreting egg-laying hormone during a prolonged period of synchronous firing called the afterdischarge. Accompanying the afterdischarge is an increase in intracellular Ca2+ and the activation of protein kinase C (PKC). We used whole cell recording from paired cultured bag cell neurons to demonstrate that electrical coupling is regulated by both Ca2+ and PKC. Elevating Ca2+ with a train of voltage steps, mimicking the onset of the afterdischarge, decreased junctional current for up to 30 min. Inhibition was most effective when Ca2+ entry occurred in both neurons. Depletion of Ca2+ from the mitochondria, but not the endoplasmic reticulum, also attenuated the electrical synapse. Buffering Ca2+ with high intracellular EGTA or inhibiting calmodulin kinase prevented uncoupling. Furthermore, activating PKC produced a small but clear decrease in junctional current, while triggering both Ca2+ influx and PKC inhibited the electrical synapse to a greater extent than Ca2+ alone. Finally, the amplitude and time course of the postsynaptic electrotonic response were attenuated after Ca2+ influx. A mathematical model of electrically connected neurons showed that excessive coupling reduced recruitment of the cells to fire, whereas less coupling led to spiking of essentially all neurons. Thus a decrease in electrical synapses could promote the afterdischarge by ensuring prompt recovery of electrotonic potentials or making the neurons more responsive to current spreading through the network.

Ethanol disrupts intestinal epithelial tight junction integrity through intracellular calcium-mediated Rho/ROCK activation

Evidence indicates that ethanol-induced intestinal barrier dysfunction and subsequent endotoxemia plays a key role in the pathogenesis of alcoholic liver disease. Recently, it has been demonstrated that ethanol induces RhoA kinase activation in intestinal epithelium, thereby disrupting barrier integrity. In this study, the role of a rise in intracellular calcium concentration ([Ca(2+)]i) in ethanol-induced Rho-associated coiled coil-forming kinase (Rho/ROCK) activation and barrier disruption was investigated in Caco-2 cell monolayers. Treatment of Caco-2 monolayers with 40 mmol/l ethanol induced [Ca(2+)]i release as indicated by increased relative fluorescent units of Fluo-3 from 0.06 ± 0.02 to 2.27 ± 1.96 (P < 0.0001). Pretreatment with 1,2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM) completely inhibited the release, whereas the inositol 1,4,5-triphosphate receptor (IP3R)-antagonist, Xestospongin C, partially inhibited the ethanol-induced [Ca(2+)]i release (from 2.27 ± 1.96 to 0.03 ± 0.01; P < 0.0001 and from 2.27 ± 1.96 to 1.19 ± 1.80; P < 0.001, respectively). The rise in [Ca(2+)]i was paralleled with increased intestinal permeability, which could be attenuated by either BAPTA-AM or Xestospongin C. Furthermore, ethanol induced Rho/ROCK activation, as indicated by increased phosphorylation of myosin-binding subunit, which could be prevented either by BAPTA, Xestospongin C, or the specific Rho/ROCK inhibitor Y27632. Finally, inhibition of Rho/ROCK kinase by Y27632 ameliorated the ethanol-induced redistribution of zonula occluden-1, adherens junction proteins including E-cadherin and β-catenin, and also disorganization of F-actin. These findings suggest that ethanol-induced [Ca(2+)]i release, mediated by stimulating IP3R-gated Ca(2+) channel, activates Rho/ROCK in Caco-2 cells, thereby contributing to ethanol-induced intestinal barrier dysfunction.

The guggulsterone derivative GG-52 inhibits NF-κB signaling in gastric epithelial cells and ameliorates ethanol-induced gastric mucosal lesions in mice

Gastric mucosal inflammation can develop after challenge with noxious stimuli such as alcohol. Specially, alcohol stimulates the release of inflammatory cytokines but does not increase gastric acid secretion, leading to gastric mucosal damage. The plant sterol guggulsterone and its novel derivative GG-52 have been reported to inhibit nuclear factor-κB (NF-κB) signaling in intestinal epithelial cells and experimental colitis. In the present study, we investigated the anti-inflammatory effects of GG-52 on gastric epithelial cells and on ethanol-induced gastric mucosal inflammation in mice. GG-52 inhibited the expression of interleukin-8 (IL-8) in gastric epithelial AGS and MKN-45 cell lines stimulated with tumor necrosis factor (TNF)-α in a dose-dependent manner. Pretreatment with GG-52 suppressed TNF-α-induced activation of IκB kinase (IKK) and NF-κB signaling in MKN-45 cells. In contrast, the inactive analog GG-46 did not produce significant changes in IL-8 expression or NF-κB activation. In a model of ethanol-induced murine gastritis, administration of GG-52 significantly reduced the severity of gastritis, as assessed by macroscopic and histological evaluation of gastric mucosal damage. In addition, the ethanol-induced upregulation of chemokine KC, a mouse homolog of IL-8, and phosphorylated p65 NF-κB signals were significantly inhibited in murine gastric mucosa pretreated with GG-52. These results indicate that GG-52 suppresses NF-κB activation in gastric epithelial cells and ameliorates ethanol-induced gastric mucosal lesions in mice, suggesting that GG-52 may be a potential gastroprotective agent.

Dantrolene blockade of ryanodine receptor impairs ethanol-induced behavioral stimulation, ethanol intake and loss of righting reflex

Calcium has been characterized as one of the most ubiquitous, universal and versatile intracellular signals. Among other substances with the ability to alter intracellular calcium levels, ethanol has been described as particularly relevant because of its social and economic impact. Ethanol effects on calcium distribution and flux in vitro have been widely studied, showing that acute ethanol administration can modulate intracellular calcium concentrations in a dose dependent manner. Intracellular calcium released from the endoplasmic reticulum plays a determinant role in several cellular processes. In this study, we aim to assess the effect of dantrolene, a ryanodine receptor antagonist, on three different ethanol-elicited behaviors: locomotor activity, loss of righting reflex and ethanol intake. Mice were challenged with an injection of dantrolene (0-5 mg/kg, i.p.) 30 min before ethanol (0-4 g/kg, i.p.) administration. Animals were immediately placed in an open field cylinder to monitor distance travelled horizontally or in a V-shaped trough to measure righting reflex recovery time. For ethanol intake, dantrolene (0-5mg/kg, i.p.) was administered 30 min before ethanol (20%, v/v) exposure, following a drinking in the dark paradigm. Our results showed that dantrolene selectively reduces ethanol-induced stimulation, loss of righting reflex, and ethanol intake in a dose dependent manner. Together, these data suggest that intracellular calcium released from the endoplasmic reticulum may play a critical role in behavioral effects caused by ethanol, and point to a calcium-dependent pathway as a possible cellular mechanism of action for ethanol.

Comparison of the efficacy of irsogladine maleate and famotidine for the healing of gastric ulcers after Helicobacter pylori eradication therapy: a randomized, controlled, prospective study

OBJECTIVE

Helicobacter pylori eradication therapy alone cannot heal gastric ulcers in Japanese patients. Irsogladine has previously been shown to accelerate the healing of gastric ulcers after H. pylori eradication therapy. And we previously reported that histamine H(2) receptor antagonists inhibit gastric ulcer relapse after H. pylori eradication therapy. We therefore compared the efficacy of irsogladine with famotidine as appropriate treatments for ulcers after eradication therapy.

METHODS

Gastric ulcer patients with H. pylori infection (n = 119) were randomized to treatment with irsogladine 4 mg/day (n = 60) or famotidine 40 mg/day (n = 59) following 1-week H. pylori eradication therapy. After treatment, assessments of gastric ulcer healing were performed.

RESULTS

The ulcer healing rates in patients receiving irsogladine and famotidine were 85.2% (46/54) and 79.6% (43/54), respectively, and were not significantly different (p = 0.4484). In the famotidine group, the healing rate was significantly lower in patients who drink alcohol than in those who do not (60.0% vs. 91.2%; p = 0.0119). However, in the irsogladine group the healing rate did not differ between patients who drink alcohol and those who do not. Furthermore, the healing rate in smokers was significantly higher in the irsogladine group (88.0%) than in the famotidine group (59.1%) (p = 0.0233).

CONCLUSIONS

Irsogladine and famotidine are both acceptable in treatment after H. pylori eradication therapy in gastric ulcer patients. Findings also suggest that irsogladine is more beneficial than famotidine in patients who drink alcohol and smoke.

Taurocholate potentiates ethanol-induced NF-kappaB activation and inhibits caspase-3 activity in cultured rat gastric mucosal cells

We have previously shown that ethanol (EtOH) induces protective NF-kappaB activation in gastric surface epithelial cells. This study investigates the defense systems in rat gastric mucosal cells (RGM-1) exposed simultaneously to EtOH and taurocholate (TC) or acetylsalicylic acid (ASA). Simultaneous exposure to ASA and EtOH increased EtOH-induced caspase-3 activity and decreased cell viability, indicating synergetic damaging action. Simultaneous exposure to TC (5 mM) with EtOH (5%) increased EtOH-induced NF-kappaB activation, opposing EtOH-induced decrease in cell membrane integrity and in cell viability as shown by decreasing RelA expression with siRNA technique. Low doses of TC decreased the EtOH (5%) induced caspase-3 activity independently from NF-kappaB pathway and inhibited EtOH-induced decrease in caspase-3 precursor protein levels, also indicating the inhibition of caspase-3 pathway. The TC (5 mM)-induced protection in EtOH exposed tissues seems to have two distinct pathways, inhibition of apoptosis and enhancement of NF-kappaB signaling.

Taurocholate-induced nitric oxide signaling and the ensuing production of reactive oxygen species lead to an increase in epithelial permeability in cultivated mouse gastric epithelium

We have here elucidated whether ulcerogenic agents affect the production of NO and reactive oxygen species (ROS). The ulcerogenic agents dose dependently induced NO and ROS production in mouse gastric epithelial cells. Taurocholate (TC, 5 mM) exposure did not affect cell viability, but it increased inducible nitric oxide synthase (iNOS) expression, NO production, ROS production, and epithelial permeability. Epithelial permeability was inhibited with NOS inhibitors or antioxidants. Oxidative stress induced by acetylsalicylic acid (ASA) and ethanol was not inhibited with NOS inhibitors. ASA induced ROS production even at low concentrations (1 mM), which did not affect cell viability. Ethanol-induced ROS production was linked to cell viability, suggesting direct oxidative stress caused by ethanol. Taurocholate-induced NO signaling and the ensuing production of ROS might contribute to initiation of defensive or adaptive cellular mechanisms. ASA-induced ROS signaling might have similar effects, whereas ethanol induced direct oxidative stress, having an influence on cell viability.

Ethanol induced NF-{kappa}B activation protects against cell injury in cultured rat gastric mucosal epithelium

Ethanol is a well-established irritant inducing inflammation in gastric mucosa, but the effects at the cellular level remain unclear. This study investigates NF-kappaB activation in gastric mucosal cells by ethanol and assesses the effects of heat shock pretreatment in this ulcerogenic situation. Rat gastric mucosal epithelia were exposed to ethanol for different time periods. Heat shock was induced by incubating the cells at 42 degrees C for 1 h prior to the experiments. For evaluation of NF-kappaB activation, the nuclear fraction of the cell lysates was analyzed with an EMSA or an ELISA-based assay. Caspase-3 (a promoter of apoptosis) activity was measured with a time-resolved fluorescence based assay, cell viability with a tetrazolium assay, and cell membrane integrity with a LDH assay. Ethanol (1-5%) induced NF-kappaB activation, reaching a maximum after 3 h, and also led to moderately increased COX-2 expression. Heat shock pretreatment and the intracellular calcium chelator BAPTA were able to inhibit ethanol-induced NF-kappaB activation. Heat shock pretreatment decreased ethanol-induced caspase-3 activation, decreased cell membrane damage, and retained cellular viability. Inhibition of NF-kappaB activation by NEMO-binding peptide, by decreasing RelA expression, or by inhibiting COX-2 activity by CAY-14040 promoted the effects of ethanol, such as increased caspase-3 activity and decreased cell viability. In conclusion, ethanol induces NF-kappaB activation via a calcium-dependent pathway and induces COX-2 expression. Inhibition of the NF-kappaB activation or COX-2 activity potentiates apoptosis and cell damage induced by ethanol, suggesting a protective role for NF-kappaB activation and COX-2 expression.

Epidermal growth factor enhances intracellular pH regulation via calcium signaling in acid-exposed primary cultured rabbit gastric epithelial cells

We have elucidated the role of different ion transporters and epidermal growth factor(EGF) during luminal acid exposure in primary cultured rabbit surface epithelial cells by measuring intracellular calcium and pH. Amiloride, DIDS, or sodium or bicarbonate substitutions were used to inhibit ion transport. During luminal acid exposure the dominant intracellular pH regulator is the Na+/H+ antiport, and bicarbonate transport has only a secondary role, which is uncovered as the Na+/H+ function fails. The decrease in intracellular pH caused by luminal acid was significantly smaller in serosal EGF-treated epithelia than in controls. This defensive function of EGF was abolished by verapamil, BAPTA, and calmidazolium but not by TMB-8. EGF increased intracellular calcium, which was prevented by verapamil but not by TMB-8. EGF enhances gastric epithelial defense against luminal acid by inducing intracellular calcium signaling via plasma membrane verapamil-sensitive calcium channels and thereby enhancing the function of the Na+/H+ antiport.

N/A

N/A

Cell volume regulation during hyperosmotic shrinkage is mediated by Na+/K+-ATPase and Na+-K+-2Cl- cotransporter in Necturus gastrics surface epithelial cells

Cell volume regulation was investigated in gastric surface epithelial cells during hypertonic conditions. Isolated Necturus antral mucosa was perfused on the serosal side with Ringer's solution (pH 7.25, 95%O2/5%CO2) and on the mucosal side successively with 150-500 mM NaCl. Amiloride, ouabain, and bumetanide were used to experimentally inhibit Na+/H+, Na+/K+ ATPase or Na+-K+-2Cl- ion transporters. Intracellular sodium activity and cell volume changes were measured with liquid sensor microelectrodes. The increase in intracellular sodium activity caused by luminal hyperosmolar exposure was mainly due to cell shrinkage. Inhibition of Na+/K+ ATPase or Na+-K+-2Cl- cotransporter increased hyperosmotic cell shrinkage (-52 +/- 5%, -85 +/- 19%, and -77 +/- 9% for control, ouabain, and bumetanide, respectively). Inhibition of Na+/K+ ATPase increased intracellular sodium activity (from 18 +/- 4 to 52 +/- 12 mM). Cell volume regulation in gastric epithelial surface cells during mucosal hyperosmolar exposure is maintained by the basolateral Na+-K+-2Cl- cotransporter, while Na+/K+ ATPase maintains sodium balance, but Na+/H+ antiport seems to have a less important role.

Ethanol modulates the VR-1 variant amiloride-insensitive salt taste receptor. II. Effect on chorda tympani salt responses

The effect of ethanol on the amiloride- and benzamil (Bz)-insensitive salt taste receptor was investigated by direct measurement of intracellular Na⁺ activity ([Na⁺]_i) using fluorescence imaging in polarized fungiform taste receptor cells (TRCs) and by chorda tympani (CT) taste nerve recordings. CT responses to KCl and NaCl were recorded in Sprague-Dawley rats, and in wild-type (WT) and vanilloid receptor-1 (VR-1) knockout mice (KO). CT responses were monitored in the presence of Bz, a specific blocker of the epithelial Na⁺ channel (ENaC). CT responses were also recorded in the presence of agonists (resiniferatoxin and elevated temperature) and antagonists (capsazepine and SB-366791) of VR-1 that similarly modulate the Bz-insensitive VR-1 variant salt taste receptor. In the absence of mineral salts, ethanol induced a transient decrease in TRC volume and elicited only transient phasic CT responses. In the presence of mineral salts, ethanol increased the apical cation flux in TRCs without a change in volume, increased transepithelial electrical resistance across the tongue, and elicited CT responses that were similar to salt responses, consisting of both a phasic component and a sustained tonic component. At concentrations <50%, ethanol enhanced responses to KCl and NaCl, while at ethanol concentrations >50%, those CT responses were inhibited. Resiniferatoxin and elevated temperature increased the sensitivity of the CT response to ethanol in salt-containing media, and SB-366791 inhibited the effect of ethanol, resiniferatoxin, and elevated temperature on the CT responses to mineral salts. VR-1 KO mice demonstrated no Bz-insensitive CT response to NaCl and no sensitivity to ethanol. We conclude that ethanol increases salt taste sensitivity by its direct action on the Bz-insensitive VR-1 variant salt taste receptor.

Ethanol modulates the VR-1 variant amiloride-insensitive salt taste receptor. I. Effect on TRC volume and Na+ flux

The effect of ethanol on the amiloride- and benzamil (Bz)-insensitive salt taste receptor was investigated by the measurement of intracellular Na(+) activity ([Na(+)](i)) in polarized rat fungiform taste receptor cells (TRCs) using fluorescence imaging and by chorda tympani (CT) taste nerve recordings. CT responses were monitored during lingual stimulation with ethanol solutions containing NaCl or KCl. CT responses were recorded in the presence of Bz (a specific blocker of the epithelial Na(+) channel [ENaC]) or the vanilloid receptor-1 (VR-1) antagonists capsazepine or SB-366791, which also block the Bz-insensitive salt taste receptor, a VR-1 variant. CT responses were recorded at 23 degrees C or 42 degrees C (a temperature at which the VR-1 variant salt taste receptor activity is maximally enhanced). In the absence of permeable cations, ethanol induced a transient decrease in TRC volume, and stimulating the tongue with ethanol solutions without added salt elicited only transient phasic CT responses that were insensitive to elevated temperature or SB-366791. Preshrinking TRCs in vivo with hypertonic mannitol (0.5 M) attenuated the magnitude of the phasic CT response, indicating that in the absence of mineral salts, transient phasic CT responses are related to the ethanol-induced osmotic shrinkage of TRCs. In the presence of mineral salts, ethanol increased the Bz-insensitive apical cation flux in TRCs without a change in cell volume, increased transepithelial electrical resistance across the tongue, and elicited CT responses that were similar to salt responses, consisting of both a transient phasic component and a sustained tonic component. Ethanol increased the Bz-insensitive NaCl CT response. This effect was further enhanced by elevating the temperature from 23 degrees C to 42 degrees C, and was blocked by SB-366791. We conclude that in the presence of mineral salts, ethanol modulates the Bz-insensitive VR-1 variant salt taste receptor.