Home About us Contact
|
Home About us Contact | ||
|
|
||
Rectifier K+ Current (rectifier + k+_current)
Kinds of Rectifier K+ Current Selected AbstractsPACAP 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] Enhancement of neuronal outward delayed rectifier K+ current by human monocyte-derived macrophagesGLIA, Issue 14 2009Dehui Hu Abstract Macrophages are critical cells in mediating the pathology of neurodegenerative disorders and enhancement of neuronal outward potassium (K+) current has implicated in neuronal apoptosis. To understand how activated macrophages induce neuronal dysfunction and injury, we studied the effects of lipopolysaccharide (LPS)-stimulated human monocytes-derived macrophage (MDM) on neuronal outward delayed rectifier K+ current (IK) and resultant change on neuronal viability in primary rat hippocampal neuronal culture. Bath application of LPS-stimulated MDM-conditioned media (MCM) enhanced neuronal IK in a concentration-dependentmanner, whereas non-stimulated MCM failed to alter neuronal IK. The enhancement of neuronal IK was repeated in a macrophage-neuronal co-culture system. The link of stimulated MCM (MCM(+))-associated enhancement of IK to MCM(+)-induced neuronal injury, as detected by PI/DAPI (propidium iodide/4,,6-diamidino-2-phenylindol) staining and MTT assay, was demonstrated by experimental results showing that addition of IK blocker tetraethylammonium to the culture protected hippocampal neurons from MCM(+)-associated challenge. Further investigation revealed elevated levels of Kv 1.3 and Kv 1.5 channel expression in hippocampal neurons after addition of MCM(+) to the culture. These results suggest that during brain inflammation macrophages, through their capacity of releasing bioactive molecules, induce neuronal injury by enhancing neuronal IK and that modulation of Kv channels is a new approach to neuroprotection. © 2009 Wiley-Liss, Inc. [source] Molecular cloning, genomic organization and functional characterization of a new short-chain potassium channel toxin-like peptide BmTxKS4 from Buthus martensii Karsch(BmK)JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 4 2004Sheng Jiqun Abstract Scorpion venom contains many small polypeptide toxins, which can modulate Na+, K+, Cl,, and Ca2+ ion,channel conductance in the cell membrane. A full-length cDNA sequence encoding a novel type of K+ -channel toxin (named BmTxKS4) was first isolated and identified from a venom gland cDNA library of Buthus martensii Karsch (BmK). The encoded precursor contains 78 amino acid residues including a putative signal peptide of 21 residues, propeptide of 11 residues, and a mature peptide of 43 residues with three disulfide bridges. BmTxKS4 shares the identical organization of disulfide bridges with all the other short-chain K+ -channel scorpion toxins. By PCR amplification of the genomic region encoding BmTxKS4, it was shown that BmTxKS4 composed of two exons is disrupted by an intron of 87 bp inserted between the first and the second codes of Phe (F) in the encoding signal peptide region, which is completely identical with that of the characterized scorpion K+ -channel ligands in the size, position, consensus junctions, putative branch point, and A+T content. The GST-BmTxKS4 fusion protein was successfully expressed in BL21 (DE3) and purified with affinity chromatography. About 2.5 mg purified recombinant BmTxKS4 (rBmTxKS4) protein was obtained by treating GST-BmTxKS4 with enterokinase and sephadex chromatography from 1 L bacterial culture. The electrophysiological activity of 1.0,M rBmTxKS4 was measured and compared by whole cell patch-clamp technique. The results indicated that rBmTxKS4 reversibly inhibited the transient outward K+ current (Ito), delayed inward rectifier K+ current (Ik1), and prolonged the action potential duration of ventricular myocyte, but it has no effect on the action potential amplitude. Taken together, BmTxKS4 is a novel subfamily member of short-strain K+ -channel scorpion toxin. © 2004 Wiley Periodicals, Inc. J Biochem Mol Toxicol 18:187,195, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20026 [source] The Kv4.2 mediates excitatory activity-dependent regulation of neuronal excitability in rat cortical neuronsJOURNAL OF NEUROCHEMISTRY, Issue 3 2008Bin Shen Abstract Neuronal excitability can cooperate with synaptic transmission to control the information storage. This regulation of neuronal plasticity can be affected by alterations in neuronal inputs and accomplished by modulation of voltage-dependent ion channels. In this study, we report that enhanced excitatory input negatively regulated neuronal excitability. Enhanced excitatory input by glutamate, electric field stimulation or high K+ increased transient outward K+ current, whereas did not affect the delayed rectifier K+ current in rat cultured cortical neurons. Both the voltage-dependent K+ channel 4.2 and 4.3 subunits contributed to the increase. The increase in the K+ current density by Kv4.2 was ascribed to its cytoplasmic membrane translocation, which was mediated by NMDA type of glutamate receptor. Furthermore, enhanced excitatory input inhibited neuronal excitability. Taken together, our results suggest that excitatory neurotransmission affects neuronal excitability via the regulation of the K+ channel membrane translocation. [source] Electrophysiological Remodeling in Human Atrial FibrillationPACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 7p2 2003DAVID R. VAN WAGONER Atrial fibrillation (AF) is a progressive disease characterized by cumulative electrophysiological and structural remodeling of the atria. Cellular electrophysiological studies have revealed marked reductions in the densities of the L-type voltage-gated Ca2+ current, ICa,L, the transient outward K+ current, ITO, and the ultra-rapid delayed rectifier K+ current, IKur, in atrial myocytes from patients in persistent or permanent AF. The density of the muscarinic K+ current (IKACh) is also reduced, however the inward rectifier K+ current (IK1) density is increased. The net shortening or lengthening of the action potential is dependent on the balance between changes in inward and outward currents. The prominent reduction in ICa,L appears to be sufficient to explain the observed decreases in action potential duration and effective refractory period that are characteristic of the fibrillating atria. Earlier studies have shown that calcium overload and perturbations in calcium handling play prominent roles in AF induced atrial remodeling. More recently, we have shown that AF is associated with evidence of oxidative injury to atrial tissue, and suggested that oxidative stress may directly contribute to the pathophysiology of AF. It is anticipated that insights gleaned from mechanistic studies will facilitate the development of improved pharmacological approaches to treat AF and to prevent the progression of arrhythmia. (PACE 2003; 26[Pt. II]:1572,1575) [source] Mechanisms by which atrial fibrillation-associated mutations in the S1 domain of KCNQ1 slow deactivation of IKs channelsTHE JOURNAL OF PHYSIOLOGY, Issue 17 2008Lioara Restier The slow delayed rectifier K+ current (IKs) is a major determinant of action potential repolarization in the heart. IKs channels are formed by coassembly of pore-forming KCNQ1 ,-subunits and ancillary KCNE1 ,-subunits. Two gain of function mutations in KCNQ1 subunits (S140G and V141M) have been associated with atrial fibrillation (AF). Previous heterologous expression studies found that both mutations caused IKs to be instantaneously activated, presumably by preventing channel closure. The purpose of this study was to refine our understanding of the channel gating defects caused by these two mutations located in the S1 domain of KCNQ1. Site-directed mutagenesis was used to replace S140 or V141 with several other natural amino acids. Wild-type and mutant channels were heterologously expressed in Xenopus oocytes and channel function was assessed with the two-microelectrode voltage clamp technique. Long intervals between voltage clamp pulses revealed that S140G and V141M KCNQ1-KCNE1 channels are not constitutively active as previously reported, but instead exhibit extremely slow deactivation. The slow component of IKs deactivation was decreased 62-fold by S140G and 140-fold by the V141M mutation. In addition, the half-point for activation of these mutant IKs channels was ,50 mV more negative than wild-type channels. Other substitutions of S140 or V141 in KCNQ1 caused variable shifts in the voltage dependence of activation, but slowed IKs deactivation to a much lesser extent than the AF-associated mutations. Based on a published structural model of KCNQ1, S140 and V141 are located near E160 in S2 and R237 in S4, two charged residues that could form a salt bridge when the channel is in the open state. In support of this model, mutational exchange of E160 and R237 residues produced a constitutively open channel. Together our findings suggest that altered charge-pair interactions within the voltage sensor module of KCNQ1 subunits may account for slowed IKs deactivation induced by S140 or V141. [source] Electrophysiological Effects of the Anti-Cancer Drug Lapatinib on Cardiac RepolarizationBASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 1 2010Hyang-Ae Lee Although lapatinib is associated with a risk of QT prolongation, the effects of the drug on cellular cardiac electrical properties and on action potential duration (APD) have not been studied. To evaluate the potential effects of lapatinib on cardiac repolarization, we investigated its electrophysiological effects using a whole-cell patch,clamp technique in transiently transfected HEK293 cells expressing human ether-à-go-go (hERG; to examine the rapidly activating delayed rectifier K+ current, IKr), KCNQ1/KCNE1 (to examine the slowly activating delayed rectifier K+ current, IKs), KCNJ2 (to examine the inwardly rectifying K+ current, IK1), or SCN5A (to examine the inward Na+ current, INa) and in rat cardiac myocytes (to examine the inward Ca2+ current, ICa). We also examined its effects on the APD at 90% (APD90) in isolated rabbit Purkinje fibres. In ion channel studies, lapatinib inhibited the hERG current in a concentration-dependent manner, with a half-maximum inhibition concentration (IC50) of 0.8 ± 0.09 ,m. In contrast, at concentrations up to 3 ,m, lapatinib did not significantly reduce the INa, IK1 or ICa amplitudes; at 3 ,m, it did slightly inhibit the IKs amplitude (by 19.4 ± 4.7%; p < 0.05). At 5 ,m, lapatinib induced prolongation of APD90 by 16.1% (p < 0.05). These results suggest that the APD90 -prolonging effect of lapatinib on rabbit Purkinje fibres is primarily a result of inhibition of the hERG current and IKs, but not INa, IK1 or ICa. [source] Combined hERG channel inhibition and disruption of trafficking in drug-induced long QT syndrome by fluoxetine: a case-study in cardiac safety pharmacologyBRITISH JOURNAL OF PHARMACOLOGY, Issue 5 2006J C Hancox Drug-induced prolongation of the rate-corrected QT interval (QTCI) on the electrocardiogram occurs as an unwanted effect of diverse clinical and investigational drugs and carries a risk of potentially fatal cardiac arrhythmias. hERG (human ether-à-go-go-related gene) is the gene encoding the ,-subunit of channels mediating the rapid delayed rectifier K+ current, which plays a vital role in repolarising the ventricles of the heart. Most QTCI prolonging drugs can inhibit the function of recombinant hERG K+ channels, consequently in vitro hERG assays are used widely as front-line screens in cardiac safety-testing of novel chemical entities. In this issue, Rajamani and colleagues report a case of QTCI prolongation with the antidepressant fluoxetine and correlate this with a dual effect of the drug and of its major metabolite norfluoxetine on hERG channels. Both compounds were found to produce an acute inhibition of the hERG channel by pharmacological blockade, but in addition they also were able to disrupt the normal trafficking of hERG protein to the cell membrane. Mutations to a key component of the drug binding site in the S6 region of the channel greatly attenuated channel block, but did not impair disruption of trafficking; this suggests that channel block and drug effects on trafficking were mediated by different mechanisms. These findings add to growing evidence for disruption of hERG channel trafficking as a mechanism for drug-induced long QT syndrome and raise questions as to possible limitations of acute screening methods in the assessment of QTcI prolonging liability of drugs in development. British Journal of Pharmacology (2006) 149, 457,459. doi:10.1038/sj.bjp.0706890 [source] Electrophysiologically "complex" glial cells freshly isolated from the hippocampus are immunopositive for the chondroitin sulfate proteoglycan NG2JOURNAL OF NEUROSCIENCE RESEARCH, Issue 6 2003Gary P. Schools Abstract We have recently described a subgroup of isolated glial fibrillary acidic protein-positive (GFAP+) hippocampal astrocytes that predominantly express outwardly rectifying currents (which we term "ORAs" for outwardly rectifying astrocytes), which are similar to the currents already described for hippocampal GFAP, "complex glia." We now report that post-recording staining of cells that were first selected as "complex" by morphology and then confirmed by their electrophysiological characteristics were NG2+ ,90% of the time. Also, the morphology of freshly isolated NG2+ cells differs from that of isolated GFAP+ ORAs in having a smaller and round cell body with thinner processes, which usually are collapsed back onto the soma. Upon detailed examination, NG2+ cells were found to differ quantitatively in some electrophysiological characteristics from GFAP+ ORAs. The outward, transient K+ currents (IKa) in the NG2+ cells showed a slower decay than the IKa in ORAs, and their density decreased in NG2+ cells from older animals. The other two major cation currents, the voltage-activated Na+ and outwardly delayed rectifier K+ currents, were similar in NG2+ cells and ORAs. To further distinguish isolated complex cells from outwardly rectifying GFAP+ astrocytes, we performed immunocytochemistry for glial markers in fixed, freshly isolated rat hippocampal glia. NG2+ cells were negative for GFAP and also for the astrocytic glutamate transporters GLT-1 and GLAST. Thus the isolated hippocampal NG2+ glial cells, though having an electrophysiological phenotype similar to that of ORAs, are an immunologically and morphologically distinct glial cell population and most likely represent NG2+ cells in situ. © 2003 Wiley-Liss, Inc. [source] | |||||||||||||