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Resting Membrane Potential (resting + membrane_potential)
Selected AbstractsThe mammalian KIR2.x inward rectifier ion channel family: expression pattern and pathophysiologyACTA PHYSIOLOGICA, Issue 3 2010T. P. De Boer Abstract Inward rectifier currents based on KIR2.x subunits are regarded as essential components for establishing a stable and negative resting membrane potential in many excitable cell types. Pharmacological inhibition, null mutation in mice and dominant positive and negative mutations in patients reveal some of the important functions of these channels in their native tissues. Here we review the complex mammalian expression pattern of KIR2.x subunits and relate these to the outcomes of functional inhibition of the resultant channels. Correlations between expression and function in muscle and bone tissue are observed, while we recognize a discrepancy between neuronal expression and function. [source] PACAP inhibits delayed rectifier potassium current via a cAMP/PKA transduction pathway: evidence for the involvement of IK in the anti-apoptotic action of PACAPEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2004Y. A. Mei Abstract Activation of potassium (K+) currents plays a critical role in the control of programmed cell death. Because pituitary adenylate cyclase-activating polypeptide (PACAP) has been shown to inhibit the apoptotic cascade in the cerebellar cortex during development, we have investigated the effect of PACAP on K+ currents in cultured cerebellar granule cells using the patch-clamp technique in the whole-cell configuration. Two types of outward K+ currents, a transient K+ current (IA) and a delayed rectifier K+ current (IK) were characterized using two different voltage protocols and specific inhibitors of K+ channels. Application of PACAP induced a reversible reduction of the IK amplitude, but did not affect IA, while the PACAP-related peptide vasoactive intestinal polypeptide had no effect on either types of K+ currents. Repeated applications of PACAP induced gradual attenuation of the electrophysiological response. In the presence of guanosine 5,-[,thio]triphosphate (GTP,S), PACAP provoked a marked and irreversible IK depression, whereas cell dialysis with guanosine 5,-[,thio]diphosphate GDP,S totally abolished the effect of PACAP. Pre-treatment of the cells with pertussis toxin did not modify the effect of PACAP on IK. In contrast, cholera toxin suppressed the PACAP-induced inhibition of IK. Exposure of granule cells to dibutyryl cyclic adenosine monophosphate (dbcAMP) mimicked the inhibitory effect of PACAP on IK. Addition of the specific protein kinase A inhibitor H89 in the patch pipette solution prevented the reduction of IK induced by both PACAP and dbcAMP. PACAP provoked a sustained increase of the resting membrane potential in cerebellar granule cells cultured either in high or low KCl-containing medium, and this long-term depolarizing effect of PACAP was mimicked by the IK specific blocker tetraethylammonium chloride (TEA). In addition, pre-incubation of granule cells with TEA suppressed the effect of PACAP on resting membrane potential. TEA mimicked the neuroprotective effect of PACAP against ethanol-induced apoptotic cell death, and the increase of caspase-3 activity observed after exposure of granule cells to ethanol was also significantly inhibited by TEA. Taken together, the present results demonstrate that, in rat cerebellar granule cells, PACAP reduces the delayed outward rectifier K+ current by activating a type 1 PACAP (PAC1) receptor coupled to the adenylyl cyclase/protein kinase A pathway through a cholera toxin-sensitive Gs protein. Our data also show that PACAP and TEA induce long-term depolarization of the resting membrane potential, promote cell survival and inhibit caspase-3 activity, suggesting that PACAP-evoked inhibition of IK contributes to the anti-apoptotic effect of the peptide on cerebellar granule cells. [source] Endothelin-1 Modulates the Arrhythmogenic Activity of Pulmonary VeinsJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 3 2008AMEYA R. UDYAVAR M.D. Objective: Endothelin-1 has important cardiovascular effects and is activated during atrial fibrillation. Pulmonary veins (PVs) play a critical role in the pathophysiology of atrial fibrillation. The aim of this study was to evaluate whether endothelin-1 affects PV arrhythmogenic activity. Methods: Conventional microelectrodes were used to record the action potentials (APs) and contractility in isolated rabbit PV tissue specimens before and after the administration of endothelin-1 (0.1, 1, 10 nM). The ionic currents of isolated PV cardiomyocytes were investigated before and after the administration of endothelin-1 (10 nM) through whole-cell patch clamps. Results: In the tissue preparation, endothelin-1 (1, 10 nM) concentration dependently shortened the AP duration and decreased the PV firing rates. Endothelin-1 (10 nM) decreased the resting membrane potential. Endothelin-1 (0.1, 1, 10 nM) decreased the contractility and increased the resting diastolic tension. In single PV cardiomyocytes, endothelin-1 (10 nM) decreased the PV firing rates from 2.7 ± 1.0 Hz to 0.8 ± 0.5 Hz (n = 16). BQ-485 (100 ,M, endothelin-1 type A receptor blocker) reversed and prevented the chrono-inhibitory effects of endothelin-1 (10 nM). Endothelin-1 (10 nM) reduced the L-type calcium currents, transient outward currents, delayed rectifier currents, transient inward currents, and sodium,calcium exchanger currents in the PV cardiomyocytes with and without pacemaker activity. Endothelin-1 (10 nM) increased the inward rectifier potassium current, hyperpolarization-induced pacemaker current, and the sustained outward potassium current in PV cardiomyocytes with and without pacemaker activity. Conclusion: Endothelin-1 may have an antiarrhythmic potential through its direct electrophysiological effects on the PV cardiomyocytes and its action on multiple ionic currents. [source] Dependence of Hyperpolarisation-Activated Cyclic Nucleotide-Gated Channel Activity on Basal Cyclic Adenosine Monophosphate Production in Spontaneously Firing GH3 CellsJOURNAL OF NEUROENDOCRINOLOGY, Issue 7 2006K. Kretschmannova Abstract The hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels play a distinct role in the control of membrane excitability in spontaneously active cardiac and neuronal cells. Here, we studied the expression and role of HCN channels in pacemaking activity, Ca2+ signalling, and prolactin secretion in GH3 immortalised pituitary cells. Reverse transcriptase-polymerase chain reaction analysis revealed the presence of mRNA transcripts for HCN2, HCN3 and HCN4 subunits in these cells. A hyperpolarisation of the membrane potential below ,,60 mV elicited a slowly activating voltage-dependent inward current (Ih) in the majority of tested cells, with a half-maximal activation voltage of ,89.9 ± 4.2 mV and with a time constant of 1.4 ± 0.2 s at ,120 mV. The bath application of 1 mM Cs+, a commonly used inorganic blocker of Ih, and 100 µM ZD7288, a specific organic blocker of Ih, inhibited Ih by 90 ± 4.1% and 84.3 ± 1.8%, respectively. Receptor- and nonreceptor-mediated activation of adenylyl and soluble guanylyl cyclase and the addition of a membrane permeable cyclic adenosine monophosphate (cAMP) analogue, 8-Br-cAMP, did not affect Ih. Inhibition of basal adenylyl cyclase activity, but not basal soluble guanylyl cyclase activity, led to a reduction in the peak amplitude and a leftward shift in the activation curve of Ih by 23.7 mV. The inhibition of the current was reversed by stimulation of adenylyl cyclase with forskolin and by the addition of 8-Br-cAMP, but not 8-Br-cGMP. Application of Cs+ had no significant effect on the resting membrane potential or electrical activity, whereas ZD7288 exhibited complex and Ih -independent effects on spontaneous electrical activity, Ca2+ signalling, and prolactin release. These results indicate that HCN channels in GH3 cells are under tonic activation by basal level of cAMP and are not critical for spontaneous firing of action potentials. [source] Regulation of Kv channel expression and neuronal excitability in rat medial nucleus of the trapezoid body maintained in organotypic cultureTHE JOURNAL OF PHYSIOLOGY, Issue 9 2010Huaxia Tong Principal neurons of the medial nucleus of the trapezoid body (MNTB) express a spectrum of voltage-dependent K+ conductances mediated by Kv1,Kv4 channels, which shape action potential (AP) firing and regulate intrinsic excitability. Postsynaptic factors influencing expression of Kv channels were explored using organotypic cultures of brainstem prepared from P9,P12 rats and maintained in either low (5 mm, low-K) or high (25 mm, high-K) [K+]o medium. Whole cell patch-clamp recordings were made after 7,28 days in vitro. MNTB neurons cultured in high-K medium maintained a single AP firing phenotype, while low-K cultures had smaller K+ currents, enhanced excitability and fired multiple APs. The calyx of Held inputs degenerated within 3 days in culture, having lost their major afferent input; this preparation of calyx-free MNTB neurons allowed the effects of postsynaptic depolarisation to be studied with minimal synaptic activity. The depolarization caused by the high-K aCSF only transiently increased spontaneous AP firing (<2 min) and did not measurably increase synaptic activity. Chronic depolarization in high-K cultures raised basal levels of [Ca2+]i, increased Kv3 currents and shortened AP half-widths. These events relied on raised [Ca2+]i, mediated by influx through voltage-gated calcium channels (VGCCs) and release from intracellular stores, causing an increase in cAMP-response element binding protein (CREB) phosphorylation. Block of VGCCs or of CREB function suppressed Kv3 currents, increased AP duration, and reduced Kv3.3 and c- fos expression. Real-time PCR revealed higher Kv3.3 and Kv1.1 mRNA in high-K compared to low-K cultures, although the increased Kv1.1 mRNA was mediated by a CREB-independent mechanism. We conclude that Kv channel expression and hence the intrinsic membrane properties of MNTB neurons are homeostatically regulated by [Ca2+]i -dependent mechanisms and influenced by sustained depolarization of the resting membrane potential. [source] Temperature-sensitive TREK currents contribute to setting the resting membrane potential in embryonic atrial myocytesTHE JOURNAL OF PHYSIOLOGY, Issue 15 2008Hengtao Zhang TREK channels belong to the superfamily of two-pore-domain K+ channels and are activated by membrane stretch, arachidonic acid, volatile anaesthetics and heat. TREK-1 is highly expressed in the atrium of the adult heart. In this study, we investigated the role of TREK-1 and TREK-2 channels in regulating the resting membrane potential (RMP) of isolated chicken embryonic cardiac myocytes. At room temperature, the average RMP of embryonic day (ED) 11 atrial myocytes was ,22 ± 2 mV. Raising the temperature to 35°C hyperpolarized the membrane to ,69 ± 2 mV and activated a large outwardly rectifying K+ current that was relatively insensitive to conventional K+ channel inhibitors (TEA, 4-AP and Ba2+) but completely inhibited by tetracaine (200 ,m), an inhibitor of TREK channels. The heat-induced hyperpolarization was mimicked by 10 ,m arachidonic acid, an agonist of TREK channels. There was little or no inwardly rectifying K+ current (IK1) in the ED11 atrial cells. In marked contrast, ED11 ventricular myocytes exhibited a normal RMP (,86.1 ± 3.4 mV) and substantial IK1, but no temperature- or tetracaine-sensitive K+ currents. Both RT-PCR and real-time PCR further demonstrated that TREK-1 and TREK-2 are highly and almost equally expressed in ED11 atrium but much less expressed in ED11 ventricle. In addition, immunofluorescence demonstrated TREK-1 protein in the membrane of atrial myocytes. These data indicate the presence and function of TREK-1 and TREK-2 in the embryonic atrium. Moreover, we demonstrate that TREK-like currents have an essential role in determining membrane potential in embryonic atrial myocytes, where IK1 is absent. [source] Changes in extracellular K+ concentration modulate contractility of rat and rabbit cardiac myocytes via the inward rectifier K+ current IK1THE JOURNAL OF PHYSIOLOGY, Issue 3 2004Ron Bouchard The mechanisms underlying the inotropic effect of reductions in [K+]o were studied using recordings of membrane potential, membrane current, cell shortening and [Ca2+]i in single, isolated cardiac myocytes. Three types of mammalian myocytes were chosen, based on differences in the current density and intrinsic voltage dependence of the inwardly rectifying background K+ current IK1 in each cell type. Rabbit ventricular myocytes had a relatively large IK1 with a prominent negative slope conductance whereas rabbit atrial cells expressed much smaller IK1, with little or no negative slope conductance. IK1 in rat ventricle was intermediate in both current density and slope conductance. Action potential duration is relatively short in both rabbit atrial and rat ventricular myocytes, and consequently both cell types spend much of the duty cycle at or near the resting membrane potential. Rapid increases or decreases of [K+]o elicited significantly different inotropic effects in rat and rabbit atrial and ventricular myocytes. Voltage-clamp and current-clamp experiments showed that the effects on cell shortening and [Ca2+]i following changes in [K+]o were primarily the result of the effects of alterations in IK1, which changed resting membrane potential and action potential waveform. This in turn differentially altered the balance of Ca2+ efflux via the sarcolemmal Na+,Ca2+ exchanger, Ca2+ influx via voltage-dependant Ca2+ channels and sarcoplasmic reticulum (SR) Ca2+ release in each cell type. These results support the hypothesis that the inotropic effect of alterations of [K+]o in the heart is due to significant non-linear changes in the current,voltage relation for IK1 and the resulting modulation of the resting membrane potential and action potential waveform. [source] Inhibitory actions of the gamma-aminobutyric acid in pediatric Sturge-Weber syndrome,ANNALS OF NEUROLOGY, Issue 2 2009Roman Tyzio PhD Objective The mechanisms of epileptogenesis in Sturge-Weber syndrome (SWS) are unknown. We explored the properties of neurons from human pediatric SWS cortex in vitro and tested in particular whether gamma-aminobutyric acid (GABA) excites neurons in SWS cortex, as has been suggested for various types of epilepsies. Methods Patch-clamp and field potential recordings and dynamic biphoton imaging were used to analyze cortical tissue samples obtained from four 6- to 14-month-old pediatric SWS patients during surgery. Results Neurons in SWS cortex were characterized by a relatively depolarized resting membrane potential, as was estimated from cell-attached recordings of N-methyl-D-aspartate channels. Many cells spontaneously fired action potentials at a rate proportional to the level of neuronal depolarization. The reversal potential for GABA-activated currents, assessed by cell-attached single channel recordings, was close to the resting membrane potential. All spontaneously firing neurons recorded in cell-attached mode or imaged with biphoton microscopy were inhibited by GABA. Spontaneous epileptiform activity in the form of recurrent population bursts was suppressed by glutamate receptor antagonists, the GABA(A) receptor agonist isoguvacine, and the positive allosteric GABA(A) modulator diazepam. Blockade of GABA(A) receptors aggravated spontaneous epileptiform activity. The NKCC1 antagonist bumetanide had little effect on epileptiform activity. Interpretation SWS cortical neurons have a relatively depolarized resting membrane potential and spontaneously fire action potentials that may contribute to increased network excitability. In contrast to previous data depicting excitatory and proconvulsive actions of GABA in certain pediatric and adult epilepsies, GABA plays mainly an inhibitory and anticonvulsive role in SWS pediatric cortex. Ann Neurol 2009;66:209,218 [source] Development of predictive quantitative retention,activity relationship models of alkaloids by mixed micellar liquid chromatographyBIOMEDICAL CHROMATOGRAPHY, Issue 2 2010Yu Chen Abstract The mixed micellar liquid chromatography is a mode that uses mixed micellar system of Brij35/SDS (85 : 15) as a mobile phase under adequate experimental conditions, can simulate the resting membrane potential and the conformation of the long hydrophilic polyoxyethylene chains remains unchanged. In this article, the applications of biopartitioning micellar chromatography, using mixed micellar system to describe and estimate bioactivities of alkaloids, has been focused. The BMCBrij35/SDS -QRAR models of half-life time, volume of distribution, plasma clearance and area under concentration,time curve were obtained using Brij35-SDS retention data. The aim is to take a look at the capability of the mixed micellar liquid chromatography model to describe and/or estimate the bioactivity of alkaloids. Copyright © 2009 John Wiley & Sons, Ltd. [source] Role of sarcoplasmic reticulum in control of membrane potential and nitrergic response in opossum lower esophageal sphincterBRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2003Yong Zhang We previously demonstrated that a balance of Ca2+ -activated Cl, current (ICl(Ca)) and K+ current activity sets the resting membrane potential of opossum lower esophageal sphincter (LES) circular smooth muscle at ,,41 mV, which leads to continuous spike-like action potentials and the generation of basal tone. Ionic mechanisms underlying this basal ICl(Ca) activity and its nitrergic regulation remain unclear. Recent studies suggest that spontaneous Ca2+ release from sarcoplasmic reticulum (SR) and myosin light chain kinase (MLCK) play important roles. The current study investigated this possibility. Conventional intracellular recordings were performed on circular smooth muscle of opossum LES. Nerve responses were evoked by electrical square wave pulses of 0.5 ms duration at 20 Hz. In the presence of nifedipine (1 ,M), substance P (1 ,M), atropine (3 ,M) and guanethidine (3 ,M), intracellular recordings demonstrated a resting membrane potential (MP) of ,38.1±0.7 mV (n=25) with spontaneous membrane potential fluctuations (MPfs) of 1,3 mV. Four pulses of nerve stimulation induced slow inhibitory junction potentials (sIJPs) with an amplitude of 6.1±0.3 mV and a half-amplitude duration of 1926±147 ms (n=25). 1H -[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a specific guanylyl cyclase inhibitor, abolished sIJPs, but had no effects on MPfs. Caffeine, a ryanodine receptor agonist, hyperpolarized MP and abolished sIJPs and MPfs. Ryanodine (20 ,M) inhibited the sIJP and induced biphasic effects on MP, an initial small hyperpolarization followed by a large depolarization. sIJPs and MPfs were also inhibited by cyclopiazonic acid, an SR Ca2+ ATPase inhibitor. Specific ICl(Ca) and MLCK inhibitors hyperpolarized the MP and inhibited MPfs and sIJPs. These data suggest that (1) spontaneous release of Ca2+ from the SR activates ICl(Ca), which in turn contributes to resting membrane potential; (2) MLCK is involved in activation of ICl(Ca); (3) inhibition of ICl(Ca) is likely to underlie sIJPs induced by nitrergic innervation. British Journal of Pharmacology (2003) 140, 1097,1107. doi:10.1038/sj.bjp.0705537 [source] Involvement of H2O2 in superoxide-dismutase-induced enhancement of endothelium-dependent relaxation in rabbit mesenteric resistance arteryBRITISH JOURNAL OF PHARMACOLOGY, Issue 2 2003Takeo Itoh The mechanism underlying the enhancement by superoxide dismutase (SOD) of endothelium-dependent relaxation was investigated in rabbit mesenteric resistance arteries. SOD (200 U ml,1) increased the production of H2O2 in smooth muscle cells (as indicated by the use of an H2O2 -sensitive fluorescent dye). Neither SOD nor catalase (400 U ml,1) modified either the resting membrane potential or the hyperpolarization induced by acetylcholine (ACh, 1 ,M) in smooth muscle cells. In arteries constricted with noradrenaline, the endothelium-dependent relaxation induced by ACh (0.01,1 ,M) was enhanced by SOD (200 U ml,1) (P<0.01). This action of SOD was inhibited by L - NG -nitroarginine (nitric oxide (NO)-synthase inhibitor) but not by either charybdotoxin+apamin (Ca2+ -activated-K+ -channel blockers) or diclofenac (cyclooxygenase inhibitor). Neither ascorbate (50 ,M) nor tiron (0.3 mM), superoxide scavengers, had any effect on the ACh-induced relaxation, but each attenuated the enhancing effect of SOD on the ACh-induced relaxation. Similarly, catalase (400 U ml,1) inhibited the effect of SOD without changing the ACh-induced relaxation. In endothelium-denuded strips constricted with noradrenaline, SOD enhanced the relaxation induced by the NO donor 1-hydroxy-2-oxo-3-(N -methyl-3-aminopropyl)-3-methyl-1-triazene (NOC-7) (P<0.05). Ascorbate and catalase each attenuated this effect of SOD. H2O2 (1 ,M) enhanced the relaxation on the noradrenaline contraction induced by NOC-7 and that induced by 8-bromo-cGMP, a membrane-permeable analogue of guanosine 3,,5, cyclic monophosphate (cGMP). SOD had no effect on cGMP production, whether measured in endothelium-intact strips following an application of ACh (0.1 ,M) or in endothelium-denuded strips following an application of NOC-7 (0.1 ,M). It is suggested that in rabbit mesenteric resistance arteries, SOD increases the ACh-induced, endothelium-dependent relaxation by enhancing the action of NO in the smooth muscle via its H2O2 -producing action (rather than via a superoxide-scavenging action). British Journal of Pharmacology (2003) 139, 444,456. doi:10.1038/sj.bjp.0705255 [source] Electrophysiological effects of endothelin-1 and their relationship to contraction in rat renal arterial smooth muscleBRITISH JOURNAL OF PHARMACOLOGY, Issue 4 2000Luisa C Betts The electophysiological effects of endothelin-1 (ET-1) and their relationship to contraction remain unclear in the renal circulation. Using endotheliumdenuded arteries from the main branch of the renal artery proximal to the kidney of the rat, we have examined its effects on tension and conducted parallel patch-clamp measurements using freshly isolated smooth muscle cells from this tissue. Pharmacological experiments revealed that ET-1 produced constriction of renal arteries dependent on the influx of extracellular Ca2+, mediated solely through ETA receptor stimulation. Current-clamp experiments revealed that renal arterial myocytes had a resting membrane potential of ,32 mV, with the majority of cells exhibiting spontaneous transient hyperpolarizations (STHPs). Application of ET-1 produced depolarization and in those cells exhibiting STHPs, either caused their inhibition or made them occur regularly. Under voltage-clamp conditions cells were observed to exhibit spontaneous transient outward currents (STOCs) inhibited by iberiotoxin. Application of voltage-ramps revealed an outward current activated at ,,30 mV, sensitive to both 4-AP and TEA. Taken together these results suggest that renal arterial myocytes possess both delayed rectifying K+ (KV) and Ca2+ -activated K+ (BKCa) channels. Under voltage-clamp, ET-1 attenuated the outward current and reduced the magnitude and incidence of STOCs: effects mediated solely as a consequence of ETA receptor stimulation. Thus, in conclusion, activation of ETA receptors by ET-1 causes inhibition of KV and BKCa channel activity, which could promote and/or maintain membrane depolarization. This effect is likely to favour L-type Ca2+ channel activity providing an influx pathway for extracellular Ca2+ essential for contraction. British Journal of Pharmacology (2000) 130, 787,796; doi:10.1038/sj.bjp.0703377 [source] Abnormal Excitability of Hippocampal CA3 Neurons in Noda Epileptic Rat (NER): Alteration of Seizure with AgingEPILEPSIA, Issue 2000Ryosuke Hanaya Purpose: Noda epileptic rat (NER), a mutant found in thc colony of Crj:Wistar rats, spontaneously shows tonic-clonic convulsions approximately once every 30 hours from 8,16 weeks of age. A long-lasting dcpolarization shift accompanied by repetitivc firings are observed in hippocampal CA3 pyramidal neurons of NER with seizures. Using hippocampal slice preparations of NER, the present electrophysiologi- cal study was performed to elucidate whether this abnormal firing in CA3 neurons developed with age and if abnormality of Ca2+ channel was involved. Methods: Hippocampal slices (40Opm) werc prepared from NER and normal Wistar rats (age; 4,29 weeks). A single rectangular pulse stimulus composed of 0.1-ms duration was delivered to the mossy fibers every 5 seconds though a bipolar electrode placed in the granular cell layer of the dentate gyrus. Intracellular recording was made from the CA3 pyramidal cell using a microelectrode containing 3M KCI intracellular recordings. A Ca2+ spike was elicited by applying a depolarizing pulse (InA, 120ms) in the cell through the recording electrode under a blockadc of Na+ and K+ channels using 1 pM tetrodotoxin and I 0mM tctraethylammonium added to the artificial CSF, respectivcly. Nicardipine (I-IOOnM), a Ca2+ channel blocker, was applicd to the bath. Results: Thirty-seven slices from I9 NER and 6 slices from 4 normal Wishe rats were used. There were no obvious changes in the resting membrane potentials of CA3 neurons between NER and Wistar rats tested. When a single stimulus was delivered to the mossy fibers, a long-lasting depolarization shift accompanied by repetitive firings followed by after-hyperpolarization werc also obtained i n hippocampal CA3 neurons of young NER (4,5 weeks of age) before occurrence of any seizurcs, although the depolarization shift in younger NER was shorter than that in NER aged more than 6 weeks. These abnormal firings werc evokcd in 58% and 30% of all CA3 neurons tested in the younger and mature NER (6,1 5 weeks of age), respectively. Furthermore, abnormal firing was not elicited in NER aged after I6 weeks. Agc-matched Wistar rats showed only single action potentials without any depolarization shift with single mossy fiber stimulation. Bath application of nicardipine (IOnM) inhibited this long-lasting depolarization shift and the accompanying repetitive firing followed by afterhypcrpolarization without affecting the first spike induced by mossy fiber stimulations. Furthermore, nicai-dipine (IOnM) inhibited the Ca2+ spikes elicited by applying a depolarizing pulse in the neurons of NER with seizures, although a higher dose (100nM) did not affect those in Wistar rats. Conclusions: These findings indicate that abnormal excitability of the NER CA3 pyramidal neurons is probably due to abnormality in the Ca2+ channcls. The abnorinal excitability was observed in NER at an age when tonic-clonic convulsions were not detected, suggesting that thc hippocampus may probably scrve as an epileptogenic focus in younger NER and the seizure impulses originating i n this area are transinittcd to the new other seizurc foci in mature NER. [source] Altered functional properties of satellite glial cells in compressed spinal gangliaGLIA, Issue 15 2009Haijun Zhang Abstract The cell bodies of sensory neurons in the dorsal root ganglion (DRG) are enveloped by satellite glial cells (SGCs). In an animal model of intervertebral foraminal stenosis and low-back pain, a chronic compression of the DRG (CCD) increases the excitability of neuronal cell bodies in the compressed ganglion. The morphological and electrophysiological properties of SGCs were investigated in both CCD and uninjured, control lumbar DRGs. SGCs responded within 12 h of the onset of CCD as indicated by an increased expression of glial fibrillary acidic protein (GFAP) in the compressed DRG but to lesser extent in neighboring or contralateral DRGs. Within 1 week, coupling through gap junctions between SGCs was significantly enhanced in the compressed ganglion. Under whole-cell patch clamp recordings, inward and outward potassium currents, but not sodium currents, were detected in individual SGCs. SGCs enveloping differently sized neurons had similar electrophysiological properties. SGCs in the compressed vs. control DRG exhibited significantly reduced inwardly rectifying potassium currents (Kir), increased input resistances and positively shifted resting membrane potentials. The reduction in Kir was greater for nociceptive medium-sized neurons compared to non-nociceptive neurons. Kir currents of SGCs around spontaneously active neurons were significantly reduced 1 day after compression but recovered by 7 days. These data demonstrate rapid alterations in glial membrane currents and GFAP expression in close temporal association with the development of neuronal hyperexcitability in the CCD model of neuropathic pain. However, these alterations are not fully sustained and suggest other mechanisms for the maintenance of the hyperexcitable state. © 2009 Wiley-Liss, Inc. [source] Characterization of the A-type potassium current in murine gastric antrumTHE JOURNAL OF PHYSIOLOGY, Issue 2 2002Gregory C. Amberg A-type currents are rapidly inactivating potassium currents that operate at subthreshold potentials. A-type currents have not been reported to occur in the phasic muscles of the stomach. We used conventional voltage-clamp techniques to identify and characterize A-type currents in myocytes isolated from the murine antrum. A-type currents were robust in these cells, with peak current densities averaging 30 pA pF,1 at 0 mV. These currents underwent rapid inactivation with a time constant of 83 ms at 0 mV. Recovery from inactivation at ,80 mV was rapid, with a time constant of 252 ms. The A-type current was blocked by 4-aminopyridine (4-AP) and was inhibited by flecainide, with an IC50 of 35 ,M. The voltage for half-activation was ,26 mV, while the voltage of half-inactivation was ,65 mV. There was significant activation and incomplete inactivation at potentials positive to ,60 mV, which is suggestive of sustained current availability in this voltage range. Under current-clamp conditions, exposure to 4-AP or flecainide depolarized the membrane potential by 7-10 mV. In intact antral tissue preparations, flecainide depolarized the membrane potential between slow waves by 5 mV; changes in slow waves were not evident. The effect of flecainide was not abolished by inhibiting enteric neurotransmission or by blocking delayed rectifier and ATP-sensitive K+ currents. Transcripts encoding Kv4 channels were detected in isolated antral myocytes by RT-PCR. Immunocytochemistry revealed intense Kv4.2- and Kv4.3-like immunoreactivity in antral myocytes. These data suggest that the A-type current in murine antral smooth muscle cells is likely to be due to Kv4 channels. This current contributes to the maintenance of negative resting membrane potentials. [source] | |||||||||||||