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1.
Activation of K(+) channels and increased migration of differentiated intestinal epithelial cells after wounding 总被引:5,自引:0,他引:5
Rao JN Platoshyn O Li L Guo X Golovina VA Yuan JX Wang JY 《American journal of physiology. Cell physiology》2002,282(4):C885-C898
Earlymucosal restitution occurs by epithelial cell migration to resealsuperficial wounds after injury. Differentiated intestinal epithelialcells induced by forced expression of the Cdx2 gene migrateover the wounded edge much faster than undifferentiated parental cellsin an in vitro model. This study determined whether thesedifferentiated intestinal epithelial cells exhibit increased migrationby altering voltage-gated K+ (Kv) channel expression andcytosolic free Ca2+ concentration([Ca2+]cyt). StableCdx2-transfected IEC-6 cells (IEC-Cdx2L1) with highly differentiated phenotype expressed higher basal levels of Kv1.1 andKv1.5 mRNAs and proteins than parental IEC-6 cells. Neither IEC-Cdx2L1cells nor parental IEC-6 cells expressed voltage-dependent Ca2+ channels. The increased expression of Kv channels indifferentiated IEC-Cdx2L1 cells was associated with an increase inwhole cell K+ currents, membrane hyperpolarization, and arise in [Ca2+]cyt. The migration rates indifferentiated IEC-Cdx2L1 cells were about four times those of parentalIEC-6 cells. Inhibition of Kv channel expression by polyamine depletiondecreased [Ca2+]cyt, reduced myosin stressfibers, and inhibited cell migration. Elevation of[Ca2+]cyt by ionomycin promoted myosin IIstress fiber formation and increased cell migration. These resultssuggest that increased migration of differentiated intestinalepithelial cells is mediated, at least partially, by increasing Kvchannel activity and Ca2+ influx during restitution. 相似文献
2.
Role of K(+) channel expression in polyamine-dependent intestinal epithelial cell migration 总被引:2,自引:0,他引:2
Wang JY Wang J Golovina VA Li L Platoshyn O Yuan JX 《American journal of physiology. Cell physiology》2000,278(2):C303-C314
Polyamines are essential for cell migrationduring early mucosal restitution after wounding in the gastrointestinaltract. Activity of voltage-gated K+ channels (Kv) controlsmembrane potential (Em) that regulates cytoplasmicfree Ca2+ concentration([Ca2+]cyt) by governing thedriving force for Ca2+ influx. This study determinedwhether polyamines are required for the stimulation of cell migrationby altering K+ channel gene expression,Em, and[Ca2+]cyt in intestinal epithelialcells (IEC-6). The specific inhibitor of polyamine synthesis,-difluoromethylornithine (DFMO, 5 mM), depleted cellularpolyamines (putrescine, spermidine, and spermine), selectivelyinhibited Kv1.1 channel (a delayed-rectifier Kv channel) expression,and resulted in membrane depolarization. Because IEC-6 cells did notexpress voltage-gated Ca2+ channels, the depolarizedEm in DFMO-treated cells decreased [Ca2+]cyt as a result of reduceddriving force for Ca2+ influx through capacitativeCa2+ entry. Migration was reduced by 80% in thepolyamine-deficient cells. Exogenous spermidine not only reversed theeffects of DFMO on Kv1.1 channel expression, Em,and [Ca2+]cyt but also restoredcell migration to normal. Removal of extracellular Ca2+ orblockade of Kv channels (by 4-aminopyridine, 1-5 mM) significantly inhibited normal cell migration and prevented the restoration of cellmigration by exogenous spermidine in polyamine-deficient cells. Theseresults suggest that polyamine-dependent intestinal epithelial cellmigration may be due partially to an increase of Kv1.1 channelexpression. The subsequent membrane hyperpolarization raises[Ca2+]cyt by increasing the drivingforce (the electrochemical gradient) for Ca2+ influx andthus stimulates cell migration. 相似文献
3.
Kv1.1 and Kv1.3 channels contribute to the delayed-rectifying K+ conductance in rat choroid plexus epithelial cells 总被引:1,自引:0,他引:1
The choroid plexuses secrete, and maintain the composition of, the cerebrospinal fluid. K+ channels play an important role in these processes. In this study the molecular identity and properties of the delayed-rectifying K+ (Kv) conductance in rat choroid plexus epithelial cells were investigated. Whole cell K+ currents were significantly reduced by 10 nM dendrotoxin-K and 1 nM margatoxin, which are specific inhibitors of Kv1.1 and Kv1.3 channels, respectively. A combination of dendrotoxin-K and margatoxin caused a depolarization of the membrane potential in current-clamp experiments. Western blot analysis indicated the presence of Kv1.1 and Kv1.3 proteins in the choroid plexus. Furthermore, the Kv1.3 and Kv1.1 proteins appear to be expressed in the apical membrane of the epithelial cells in immunocytochemical studies. The Kv conductance was inhibited by 1 µM serotonin (5-HT), with maximum inhibition to 48% of control occurring in 8 min (P < 0.05 by Student's t-test for paired data). Channel inhibition by 5-HT was prevented by the 5-HT2C antagonist mesulergine (300 nM). It was also attenuated in the presence of calphostin C (a protein kinase C inhibitor). The conductance was partially inhibited by 1,2-dioctanoyl-sn-glycerol and phorbol 12-myristate 13-acetate, both of which activate protein kinase C. These data suggest that 5-HT acts at 5-HT2C receptors to activate protein kinase C, which inhibits the Kv channels. In conclusion, Kv1.1 and Kv1.3 channels make a significant contribution to K+ efflux at the apical membrane of the choroid plexus. delayed-rectifying potassium channel; serotonin 相似文献
4.
Apoptosis repressor with caspase domain inhibits cardiomyocyte apoptosis by reducing K+ currents 总被引:8,自引:0,他引:8
Ekhterae D Platoshyn O Zhang S Remillard CV Yuan JX 《American journal of physiology. Cell physiology》2003,284(6):C1405-C1410
Cell shrinkageis an early prerequisite in programmed cell death, and cytoplasmicK+ is a dominant cation that controls intracellular ionhomeostasis and cell volume. Blockade of K+ channelsinhibits apoptotic cell shrinkage and attenuates apoptosis. We examined whether apoptotic repressor with caspase recruitment domain (ARC), an antiapoptotic protein, inhibits cardiomyocyte apoptosis by reducing K+ efflux throughvoltage-gated K+ (Kv) channels. In heart-derived H9c2cells, whole cell Kv currents (IK(V)) wereisolated by using Ca2+-free extracellular (bath) solutionand including 5 mM ATP and 10 mM EGTA in the intracellular (pipette)solution. Extracellular application of 5 mM 4-aminopyridine (4-AP), ablocker of Kv channels, reversibly reduced IK(V)by 50-60% in H9c2 cells. The remaining currents during 4-APtreatment may be generated by K+ efflux through4-AP-insensitive K+ channels. Overexpression of ARC inheart-derived H9c2 cells significantly decreasedIK(V), whereas treatment with staurosporine, apotent apoptosis inducer, enhanced IK(V)in wild-type cells. The staurosporine-induced increase inIK(V) was significantly suppressed and thestaurosporine-mediated apoptosis was markedly inhibited incells overexpressing ARC compared with cells transfected with thecontrol neomycin vector. These results suggest that theantiapoptotic effect of ARC is, in part, due to inhibition of Kvchannels in cardiomyocytes. 相似文献
5.
Potassium Channels at Chara Plasmalemma 总被引:2,自引:0,他引:2
Exposure to high K+ medium transforms Chara plasmalemma into[K+]osensitive state (K+ state). The current-voltage (I/V)characteristicsunder such conditions display a negative conductance region.This feature results from the complex time and voltage dependenceof K+ channel opening At potentials more negative than a thresholdp.d. the channels are closed and the I/V characteristics becomelinear with a low slope conductance of 0.8 S m2 and only a weakdependence on [K+]o. Such behaviour is usually associated witha non-specific leak current The threshold level for K+ channelclosing depends on [K+]o. In 2.0 mol m3 and 5.0 mol m3K+ medium the membrane resting p.d. follows EK, but hyperpolarizesgradually if the [K+]o is lowered. The proton pump thus appearsto be non-operative, while the cell is in the K+ state, andrecovers slowly as the cell is returned to a low K+ medium.Excitation currents decline if the cells are kept in K+ statefor some hours. Key words: K+ channels, Chara corallina, Proton pump, Current/, oltage characteristics, Conductance 相似文献
6.
Distinct K+ conductive pathways are required for Cl- and K+ secretion across distal colonic epithelium 总被引:1,自引:0,他引:1
Secretion of Cl and K+ in the colonic epithelium operates through a cellular mechanism requiring K+ channels in the basolateral and apical membranes. Transepithelial current [short-circuit current (Isc)] and conductance (Gt) were measured for isolated distal colonic mucosa during secretory activation by epinephrine (Epi) or PGE2 and synergistically by PGE2 and carbachol (PGE2 + CCh). TRAM-34 at 0.5 µM, an inhibitor of KCa3.1 (IK, Kcnn4) K+ channels (H. Wulff, M. J. Miller, W. Hänsel, S. Grissmer, M. D. Cahalan, and K. G. Chandy. Proc Natl Acad Sci USA 97: 81518156, 2000), did not alter secretory Isc or Gt in guinea pig or rat colon. The presence of KCa3.1 in the mucosa was confirmed by immunoblot and immunofluorescence detection. At 100 µM, TRAM-34 inhibited Isc and Gt activated by Epi (4%), PGE2 (30%) and PGE2 + CCh (60%). The IC50 of 4.0 µM implicated involvement of K+ channels other than KCa3.1. The secretory responses augmented by the K+ channel opener 1-EBIO were inhibited only at a high concentration of TRAM-34, suggesting further that KCa3.1 was not involved. Sensitivity of the synergistic response (PGE2 + CCh) to a high concentration TRAM-34 supported a requirement for multiple K+ conductive pathways in secretion. Clofilium (100 µM), a quaternary ammonium, inhibited Cl secretory Isc and Gt activated by PGE2 (20%) but not K+ secretion activated by Epi. Thus Cl secretion activated by physiological secretagogues occurred without apparent activity of KCa3.1 channels but was dependent on other types of K+ channels sensitive to high concentrations of TRAM-34 and/or clofilium. epinephrine; prostaglandin E2; cholinergic; Kcnn4; TRAM-34; clofilium 相似文献
7.
Potassium channel expression level is dependent on the proliferation state in the GH3 pituitary cell line 总被引:7,自引:0,他引:7
Czarnecki A Dufy-Barbe L Huet S Odessa MF Bresson-Bepoldin L 《American journal of physiology. Cell physiology》2003,284(4):C1054-C1064
Previously, we showed that the peakdensity of the transient outward K+ current(Ito) expressed in GH3 cells was different inthe S phase than in other phases of the cell cycle. Using cellsynchronization, we show here that Ito dropsprecisely at the quiescent (G0 phase)/proliferating transition. This change is not due to a modification in the voltage dependence of Ito, but rather to a modificationin its inactivation kinetics. Molecular determination of K+channel subunits showed that Ito required theexpression of Kv1.4, Kv4.1, and Kv4.3. We found that the increase inIto density during the quiescent state wasaccompanied by an increase in Kv1.4 protein expression, whereas Kv4.3expression remained unchanged. We further demonstrate that the linkbetween Ito expression and cell proliferation isnot mediated by variations in cell excitability. These results providenew evidence for the cell cycle dependence ofIto expression, which could be relevant inunderstanding the mechanisms leading to pituitary adenomas. 相似文献
8.
Escobar LI Martínez-Téllez JC Salas M Castilla SA Carrisoza R Tapia D Vázquez M Bargas J Bolívar JJ 《American journal of physiology. Cell physiology》2004,286(4):C965-C974
We studied the K+-selective conductances in primary cultures of rat renal inner medullary collecting duct (IMCD) using perforated-patch and conventional whole cell techniques. Depolarizations above 20 mV induced a time-dependent outward K+ current (Ivto) similar to a delayed rectifier. Ivto showed a half-maximal activation around 5.6 mV with a slope factor of 6.8 mV. Its K+/Na+ selectivity ratio was 11.7. It was inhibited by tetraethylammonium, quinidine, 4-aminopyridine, and Ba2+ and was not Ca2+ dependent. The delayed rectifying characteristics of Ivto prompted us to screen the expression of Kv1 and Kv3 families by RT-PCR. Analysis of RNA isolated from cell cultures revealed the presence of three Kv -subunits (Kv1.1, Kv1.3, and Kv1.6). Western blot analysis with Kv -subunit antibodies for Kv1.1 and Kv1.3 showed labeling of 70-kDa proteins from inner medulla plasmatic and microsome membranes. Immunocytochemical analysis of cell culture and kidney inner medulla showed that Kv1.3 is colocalized with the Na+-K+-ATPase at the basolateral membrane, although it is also in the cytoplasm. This is the first evidence of recording, protein expression, and localization of a voltage-gated Kv1 in the kidney IMCD cells. kidney; Kv1.3; potassium channel; potassium transport; whole cell clamp; immunocytochemistry; confocal microscopy 相似文献
9.
Ko EA Burg ED Platoshyn O Msefya J Firth AL Yuan JX 《American journal of physiology. Cell physiology》2007,293(3):C928-C937
Mice are useful animal models to study pathogenic mechanisms involved in pulmonary vascular disease. Altered expression and function of voltage-gated K+ (KV) channels in pulmonary artery smooth muscle cells (PASMCs) have been implicated in the development of pulmonary arterial hypertension. KV currents (IK(V)) in mouse PASMCs have not been comprehensively characterized. The main focus of this study was to determine the biophysical and pharmacological properties of IK(V) in freshly dissociated mouse PASMCs with the patch-clamp technique. Three distinct whole cell IK(V) were identified based on the kinetics of activation and inactivation: rapidly activating and noninactivating currents (in 58% of the cells tested), rapidly activating and slowly inactivating currents (23%), and slowly activating and noninactivating currents (17%). Of the cells that demonstrated the rapidly activating noninactivating current, 69% showed IK(V) inhibition with 4-aminopyridine (4-AP), while 31% were unaffected. Whole cell IK(V) were very sensitive to tetraethylammonium (TEA), as 1 mM TEA decreased the current amplitude by 32% while it took 10 mM 4-AP to decrease IK(V) by a similar amount (37%). Contribution of Ca2+-activated K+ (KCa) channels to whole cell IK(V) was minimal, as neither pharmacological inhibition with charybdotoxin or iberiotoxin nor perfusion with Ca2+-free solution had an effect on the whole cell IK(V). Steady-state activation and inactivation curves revealed a window K+ current between –40 and –10 mV with a peak at –31.5 mV. Single-channel recordings revealed large-, intermediate-, and small-amplitude currents, with an averaged slope conductance of 119.4 ± 2.7, 79.8 ± 2.8, 46.0 ± 2.2, and 23.6 ± 0.6 pS, respectively. These studies provide detailed electrophysiological and pharmacological profiles of the native KV currents in mouse PASMCs. KV channels 相似文献
10.
Brevnova EE Platoshyn O Zhang S Yuan JX 《American journal of physiology. Cell physiology》2004,287(3):C715-C722
Apoptotic cell shrinkage, an early hallmark of apoptosis, is regulated by K+ efflux and K+ channel activity. Inhibited apoptosis and downregulated K+ channels in pulmonary artery smooth muscle cells (PASMC) have been implicated in development of pulmonary vascular medial hypertrophy and pulmonary hypertension. The objective of this study was to test the hypothesis that overexpression of KCNA5, which encodes a delayed-rectifier voltage-gated K+ (Kv) channel, increases K+ currents and enhances apoptosis. Transient transfection of KCNA5 caused 25- to 34-fold increase in KCNA5 channel protein level and 24- to 29-fold increase in Kv channel current (IK(V)) at +60 mV in COS-7 and rat PASMC, respectively. In KCNA5-transfected COS-7 cells, staurosporine (ST)-mediated increases in caspase-3 activity and the percentage of cells undergoing apoptosis were both enhanced, whereas basal apoptosis (without ST stimulation) was unchanged compared with cells transfected with an empty vector. In rat PASMC, however, transfection of KCNA5 alone caused marked increase in basal apoptosis, in addition to enhancing ST-mediated apoptosis. Furthermore, ST-induced apoptotic cell shrinkage was significantly accelerated in COS-7 cells and rat PASMC transfected with KCNA5, and blockade of KCNA5 channels with 4-aminopyridine (4-AP) reduced K+ currents through KCNA5 channels and inhibited ST-induced apoptosis in KCNA5-transfected COS-7 cells. Overexpression of the human KCNA5 gene increases K+ currents (i.e., K+ efflux or loss), accelerates apoptotic volume decrease (AVD), increases caspase-3 activity, and induces apoptosis. Induction of apoptosis in PASMC by KCNA5 gene transfer may serve as an important strategy for preventing the progression of pulmonary vascular wall thickening and for treating patients with idiopathic pulmonary arterial hypertension (IPAH). potassium ion channel; pulmonary hypertension 相似文献
11.
The dependence of membrane potentials on changes in the extra-cellularK+ concentration [K+]e was investigated in potato tuber sliceswith dripping perfusion, and in growing Vigna hypocotyl segmentswith pressurized intra-organ perfusion methods. Only under anoxiawere the membrane potential of potato tuber slices and the electricpotential difference between the parenchyma symplast and xylem(Vpx) of Vigna hypocotyl segments depolarized markedly (46 mVand 42 mV/log[K+]e unit, respectively) with increasing [K+]eabove the critical values. The electric potential differencebetween the parenchyma symplast and organ surface (Vps of thehypocotyl segments remained nearly unchanged up to 30 mEq [K+]e.Under highly aerobic conditions the membrane potentials wererelatively independent of [K+]e except at very high K+ concentrations.Vps showed even hyperpolarization with the increasing KCl concentrationin the perfusion solution that is not in direct contact withthe surface membrane of the parenchyma symplast. The respiration-dependentelectrogenic components of the membrane potentials regularlyincreased with the increasing [K+]e. A voltage-dependent homeostaticcontrol of membrane potential is discussed. (Received August 13, 1984; Accepted December 21, 1984) 相似文献
12.
K+ channel KVLQT1 located in the basolateral membrane of distal colonic epithelium is not essential for activating Cl- secretion 总被引:1,自引:0,他引:1
Liao T Wang L Halm ST Lu L Fyffe RE Halm DR 《American journal of physiology. Cell physiology》2005,289(3):C564-C575
The cellular mechanism for Cl and K+ secretion in the colonic epithelium requires K+ channels in the basolateral and apical membranes. Colonic mucosa from guinea pig and rat were fixed, sectioned, and then probed with antibodies to the K+ channel proteins KVLQT1 (Kcnq1) and minK-related peptide 2 (MiRP2, Kcne3). Immunofluorescence labeling for Kcnq1 was most prominent in the lateral membrane of crypt cells in rat colon. The guinea pig distal colon had distinct lateral membrane immunoreactivity for Kcnq1 in crypt and surface cells. In addition, Kcne3, an auxiliary subunit for Kcnq1, was detected in the lateral membrane of crypt and surface cells in guinea pig distal colon. Transepithelial short-circuit current (Isc) and transepithelial conductance (Gt) were measured for colonic mucosa during secretory activation by epinephrine (EPI), prostaglandin E2 (PGE2), and carbachol (CCh). HMR1556 (10 µM), an inhibitor of Kcnq1 channels (Gerlach U, Brendel J, Lang HJ, Paulus EF, Weidmann K, Brüggemann A, Busch A, Suessbrich H, Bleich M, and Greger R. J Med Chem 44: 38313837, 2001), partially (50%) inhibited Cl secretory Isc and Gt activated by PGE2 and CCh in rat colon with an IC50 of 55 nM, but in guinea pig distal colon Cl secretory Isc and Gt were unaltered. EPI-activated K+-secretory Isc and Gt also were essentially unaltered by HMR1556 in both rat and guinea pig colon. Although immunofluorescence labeling with a Kcnq1 antibody supported the basolateral membrane presence in colonic epithelium of the guinea pig as well as the rat, the Kcnq1 K+ channel is not an essential component for producing Cl secretion. Other K+ channels present in the basolateral membrane presumably must also contribute directly to the K+ conductance necessary for K+ exit during activation of Cl secretion in the colonic mucosa. HMR1556; K+ secretion; epinephrine; prostaglandin E2; cholinergic 相似文献
13.
Sustained membrane depolarization and pulmonary artery smooth muscle cell proliferation 总被引:16,自引:0,他引:16
Platoshyn O Golovina VA Bailey CL Limsuwan A Krick S Juhaszova M Seiden JE Rubin LJ Yuan JX 《American journal of physiology. Cell physiology》2000,279(5):C1540-C1549
Pulmonary vasoconstriction and vascularmedial hypertrophy greatly contribute to the elevated pulmonaryvascular resistance in patients with pulmonary hypertension. A rise incytosolic free Ca2+ ([Ca2+]cyt)in pulmonary artery smooth muscle cells (PASMC) triggers vasoconstriction and stimulates cell growth. Membrane potential (Em) regulates[Ca2+]cyt by governing Ca2+influx through voltage-dependent Ca2+ channels. Thusintracellular Ca2+ may serve as a shared signaltransduction element that leads to pulmonary vasoconstriction andvascular remodeling. In PASMC, activity of voltage-gated K+(Kv) channels regulates resting Em. In thisstudy, we investigated whether changes of Kv currents[IK(V)], Em, and[Ca2+]cyt affect cell growth by comparingthese parameters in proliferating and growth-arrested PASMC. Serumdeprivation induced growth arrest of PASMC, whereas chelation ofextracellular Ca2+ abolished PASMC growth. Resting[Ca2+]cyt was significantly higher, andresting Em was more depolarized, inproliferating PASMC than in growth-arrested cells. Consistently, wholecell IK(V) was significantly attenuated in PASMCduring proliferation. Furthermore, Emdepolarization significantly increased resting[Ca2+]cyt and augmented agonist-mediatedrises in [Ca2+]cyt in the absence ofextracellular Ca2+. These results demonstrate that reducedIK(V), depolarized Em, and elevated [Ca2+]cyt may play a criticalrole in stimulating PASMC proliferation. Pulmonary vascular medialhypertrophy in patients with pulmonary hypertension may be partlycaused by a membrane depolarization-mediated increase in[Ca2+]cyt in PASMC. 相似文献
14.
MEMON ABDUL RAZAQUE; SIDDIQI M. YAEESH; CLASS ANTHONY D. M. 《Journal of experimental botany》1985,36(1):79-90
Barley (Hordeum vulgare L.) varieties differed in their raponseto [K+]0, in terms of their utilization efficiencies (UE = freshweight. concentration of [K+]11). At low [K+]0, Compana,an efficient-non-responder demonstrated superior utilizationof absorbed K+. On the other hand, at high [K+]0, Fergus (anefficient responder) and BT 334 (an inefficient responder) hadhigher UE values for K+ than Compana which performed poorlyat this [K+]0. Kinetic parameters for K+ activation of the enzyme pyruvatekinase from 12 barley varieties, representing a range of UEvalues, were determined. Varieties showed substantial differencesin their Vmax values (P<0·01). Compana, an efficientvariety, had the highest Vmax (31 µmol g1 freshwt. h1) which was about 50% higher than that of Mingo,an inefficient variety. By contrast, Km values for the enzymeswere not significantly different among varieties The mean valuesfor all varieties (3·9±0·15 mol m3K+) is far below the estimated cytoplasmic [K+] (100-200 molm3). It is, therefore, unlikely that differences in theutilization of K+ by these varieties can be explained on thebasis of differential requirements for (K+) activation of theseenzymes. Alternative possibilities for differences in the utilizationof K+ are discussed. Key words: K+ utilization efficiency, Pyruvate kinase, Barley varieties 相似文献
15.
pH-dependent modulation of Kv1.3 inactivation: role of His399 总被引:2,自引:0,他引:2
Somodi S Varga Z Hajdu P Starkus JG Levy DI Gáspár R Panyi G 《American journal of physiology. Cell physiology》2004,287(4):C1067-C1076
The Kv1.3 K+ channel lacks N-type inactivation, but during prolonged depolarized periods it inactivates via the slow (P/C type) mechanism. It bears a titratable histidine residue in position 399 (equivalent of Shaker 449), a site known to influence the rate of slow inactivation. As opposed to several other voltage-gated K+ channels, slow inactivation of Kv1.3 is slowed when extracellular pH (pHo) is lowered under physiological conditions. Our findings are as follows. First, when His399 was mutated to a lysine, arginine, leucine, valine or tyrosine, extracellular acidification (pH 5.5) accelerated inactivation reminiscent of other Kv channels. Second, inactivation of the wild-type channel was accelerated by low pHo when the ionic strength of the external solution was raised. Inactivation of the H399K mutant was also accelerated by high ionic strength at pH 7.35 but not the inactivation of H399L. Third, after the external application of blocking barium ions, recovery of the wild-type current during washout was slower in low pHo. Fourth, the dissociation rate of Ba2+ was pH insensitive for both H399K and H399L. Furthermore, Ba2+ dissociation rates were equal for H399K and the wild type at pH 5.5 and were equal for H399L and the wild type at pH 7.35. These observations support a model in which the electric field of the protonated histidines creates a potential barrier for potassium ions just outside the external mouth of the pore that hinders their exit from the binding site controlling inactivation. In Kv1.3, this effect overrides the generally observed speeding of slow inactivation when pHo is reduced. extracellular pH; potassium channel; histidine; barium; high ionic strength 相似文献
16.
Zhang L Foster K Li Q Martens JR 《American journal of physiology. Cell physiology》2007,293(1):C152-C161
The number of ion channels expressed on the cell surface shapes the complex electrical response of excitable cells. An imbalance in the ratio of inward and outward conducting channels is unfavorable and often detrimental. For example, over- or underexpression of voltage-gated K+ (Kv) channels can be cytotoxic and in some cases lead to disease. In this study, we demonstrated a novel role for S-acylation in Kv1.5 cell surface expression. In transfected fibroblasts, biochemical evidence showed that Kv1.5 is posttranslationally modified on both the NH2 and COOH termini via hydroxylamine-sensitive thioester bonds. Pharmacological inhibition of S-acylation, but not myristoylation, significantly decreased Kv1.5 expression and resulted in accumulation of channel protein in intracellular compartments and targeting for degradation. Channel protein degradation was rescued by treatment with proteasome inhibitors. Time course experiments revealed that S-acylation occurred in the biosynthetic pathway of nascent channel protein and showed that newly synthesized Kv1.5 protein, but not protein expressed on the cell surface, is sensitive to inhibitors of thioacylation. Sensitivity to inhibitors of S-acylation was governed by COOH-terminal, but not NH2-terminal, cysteines. Surprisingly, although intracellular cysteines were required for S-acylation, mutation of these residues resulted in an increase in Kv1.5 cell surface channel expression, suggesting that screening of free cysteines by fatty acylation is an important regulatory step in the quality control pathway. Together, these results show that S-acylation can regulate steady-state expression of Kv1.5. quality control; potassium; channels; palmitoylation; posttranslational 相似文献
17.
In order to express selectivity of ion channels, it is commonto determine the reversal voltages, Vr in the presence of differention species, and to convert these voltages to permeability ratiosby constant field equations, which are based on independentelectro-diffusion. In the case of individual ion channels, competitionrather than independence can be expected. This situation hasbeen described here in terms of a catalytic reaction cycle fora channel which may translocate K+ as well as Ca2+ . An exampleis given, where the fundamental rate constants for the K+ cycleand for the Ca2+ cycle are the same, and opposing 1:10 concentrationgradients for Ca2+ and for K+ are applied. In this case, thereversal voltage of the resultant total current is so closeto the equilibrium voltage of Ca2+, that constant field calculationwould yield an overestimated permeability ratio PCa:PK of about10. Two limiting cases are pointed out. In the case of dilutesolution, the ions move independently and the system can obeythe constant field theory. At high concentrations, the systemapproaches complete dependence and will consequently behaveas an antiporter. Key words: Antiport, calcium permeability, channel selectivity, competitive catalysis, enzyme kinetics 相似文献
18.
Dependence of Na+-K+ pump current-voltage relationship on intracellular Na+, K+, and Cs+ in rabbit cardiac myocytes 总被引:2,自引:0,他引:2
Hansen PS Buhagiar KA Kong BY Clarke RJ Gray DF Rasmussen HH 《American journal of physiology. Cell physiology》2002,283(5):C1511-C1521
To examine effects of cytosolicNa+, K+, and Cs+ on the voltagedependence of the Na+-K+ pump, we measuredNa+-K+ pump current (Ip)of ventricular myocytes voltage-clamped at potentials(Vm) from 100 to +60 mV. Superfusates weredesigned to eliminate voltage dependence at extracellular pump sites.The cytosolic compartment of myocytes was perfused with patch pipette solutions with a Na+ concentration ([Na]pip)of 80 mM and a K+ concentration from 0 to 80 mM or withsolutions containing Na+ in concentrations from 0.1 to 100 mM and K+ in a concentration of either 0 or 80 mM. When[Na]pip was 80 mM, K+ in pipette solutionshad a voltage-dependent inhibitory effect on Ipand induced a negative slope of theIp-Vm relationship. Cs+ in pipette solutions had an effect onIp qualitatively similar to that ofK+. Increases in Ip with increasesin [Na]pip were voltage dependent. The dielectriccoefficient derived from[Na]pip-Ip relationships at thedifferent test potentials was 0.15 when pipette solutions included 80 mM K+ and 0.06 when pipette solutions were K+ free. 相似文献
19.
Putzke C Hanley PJ Schlichthörl G Preisig-Müller R Rinné S Anetseder M Eckenhoff R Berkowitz C Vassiliou T Wulf H Eberhart L 《American journal of physiology. Cell physiology》2007,293(4):C1319-C1326
Volatile anesthetics have been shown to activate various two-pore (2P) domain K+ (K2P) channels such as TASK-1 and TREK-1 (TWIK-related acid-sensitive K+ channel), and mice deficient in these channels are resistant to halothane-induced anesthesia. Here, we investigated whether K2P channels were also potentially important targets of intravenous anesthetics. Whole cell patch-clamp techniques were used to determine the effects of the commonly used intravenous anesthetics etomidate and propofol on the acid-sensitive K+ current in rat ventricular myocytes (which strongly express TASK-1) and selected human K2P channels expressed in Xenopus laevis oocytes. In myocytes, etomidate decreased both inward rectifier K+ (Kir) current (IK1) and acid-sensitive outward K+ current at positive potentials, suggesting that this drug may inhibit TASK channels. Indeed, in addition to inhibiting guinea pig Kir2.1 expressed in oocytes, etomidate inhibited human TASK-1 (and TASK-3) in a concentration-dependent fashion. Propofol had no effect on human TASK-1 (or TASK-3) expressed in oocytes. Moreover, we showed that, similar to the known effect of halothane, sevoflurane and the purified R-(–)- and S-(+)-enantiomers of isoflurane, without stereoselectivity, activated human TASK-1. We conclude that intravenous and volatile anesthetics have dissimilar effects on K2P channels. Human TASK-1 (and TASK-3) are insensitive to propofol but are inhibited by supraclinical concentrations of etomidate. In contrast, stimulatory effects of sevoflurane and enantiomeric isoflurane on human TASK-1 can be observed at clinically relevant concentrations. volatile anesthetics; etomidate; propofol; ion channels 相似文献
20.
Differential contribution of sialic acid to the function of repolarizing K+ currents in ventricular myocytes 总被引:3,自引:0,他引:3
Ufret-Vincenty Carmen A.; Baro Deborah J.; Santana L. F. 《American journal of physiology. Cell physiology》2001,281(2):C464
Weinvestigated the contribution of sialic acid residues to theK+ currents involved in the repolarization of mouseventricular myocytes. Ventricular K+ currents had a rapidlyinactivating component followed by slowly decaying and sustainedcomponents. This current was produced by the summation of threedistinct currents: Ito, which contributed to thetransient component; Iss, which contributed tothe sustained component; and IK,slow, whichcontributed to both components. Incubation of ventricular myocytes withthe sialidase neuraminidase reduced the amplitude ofIto without alteringIK,slow and Iss. We foundthat the reduction in Ito amplitude resultedfrom a depolarizing shift in the voltage of activation and a reductionin the conductance of Ito. Expression of Kv4.3channels, a major contributor to Ito in theventricle, in a sialylation-deficient Chinese hamster ovary cell line(lec2) mimicked the effects of neuraminidase on the ventricularIto. Furthermore, we showed that sialylatedglycolipids have little effect on the voltage dependence ofIto. Finally, consistent with its actions onIto, neuraminidase produced an increase in theduration of the action potential of ventricular myocytes and thefrequency of early afterdepolarizations. We conclude that sialylationof the proteins forming Kv4 channels is important in determining thevoltage dependence and conductance of Ito and that incomplete glycosylation of these channels could lead to arrhythmias. 相似文献