共查询到20条相似文献,搜索用时 31 毫秒
1.
Yu. D. Stepanenko T. V. Karelina D. A. Sibarov P. A. Abushik S. M. Antonov 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2017,11(3):248-251
Here we show that positive modulators (CyPPA and NS309) of Ca2+-activated K+ channels of small (SK) and intermediate (IK) conductances in cerebellar neurons decrease glutamate-evoked Ca2+ entry into neurons independently on the presence of Mg2+ in extracellular media. An analysis of neuronal viability after long-term (240 min) glutamate treatments demonstrated neuroprotective action of CyPPA and NS309. Extracellular Mg2+ did not protect neurons from apoptosis during prolonged treatment with glutamate. Activation of SK and IK channels results in local membrane hyperpolarization, which enhances Mg2+ block of NMDA receptors and reduces activation of voltage-dependent Ca2+ channels, which can explain neuroprotection caused by CyPPA or NS309. The obtained results reveal an important role Ca2+-activated K+ channels of small and intermediate conductance in the regulation of Ca2+ entry into cerebellar neurons via NMDA receptors and voltage-gated Ca2+ channels. 相似文献
2.
Jonathan Berrout Mykola Mamenko Oleg L. Zaika Lihe Chen Wenzheng Zang Oleh Pochynyuk Roger G. O'Neil 《PloS one》2014,9(4)
The Ca2+-activated, maxi-K (BK) K+ channel, with low Ca2+-binding affinity, is expressed in the distal tubule of the nephron and contributes to flow-dependent K+ secretion. In the present study we demonstrate that the Ca2+-activated, SK3 (KCa2.3) K+ channel, with high Ca2+-binding affinity, is also expressed in the mouse kidney (RT-PCR, immunoblots). Immunohistochemical evaluations using tubule specific markers demonstrate significant expression of SK3 in the distal tubule and the entire collecting duct system, including the connecting tubule (CNT) and cortical collecting duct (CCD). In CNT and CCD, main sites for K+ secretion, the highest levels of expression were along the apical (luminal) cell membranes, including for both principal cells (PCs) and intercalated cells (ICs), posturing the channel for Ca2+-dependent K+ secretion. Fluorescent assessment of cell membrane potential in native, split-opened CCD, demonstrated that selective activation of the Ca2+-permeable TRPV4 channel, thereby inducing Ca2+ influx and elevating intracellular Ca2+ levels, activated both the SK3 channel and the BK channel leading to hyperpolarization of the cell membrane. The hyperpolarization response was decreased to a similar extent by either inhibition of SK3 channel with the selective SK antagonist, apamin, or by inhibition of the BK channel with the selective antagonist, iberiotoxin (IbTX). Addition of both inhibitors produced a further depolarization, indicating cooperative effects of the two channels on Vm. It is concluded that SK3 is functionally expressed in the distal nephron and collecting ducts where induction of TRPV4-mediated Ca2+ influx, leading to elevated intracellular Ca2+ levels, activates this high Ca2+-affinity K+ channel. Further, with sites of expression localized to the apical cell membrane, especially in the CNT and CCD, SK3 is poised to be a key pathway for Ca2+-dependent regulation of membrane potential and K+ secretion. 相似文献
3.
Koh-Ichi Enomoto Kishio Furuya Takashi Maeno Charles Edwards Takami Oka 《The Journal of membrane biology》1991,119(2):133-139
Summary Calcium-activated potassium channels were the channels most frequently observed in primary cultured normal mammary cell and in the established mammary tumor cell, MMT060562. In both cells, single-channel and whole-cell clamp recordings sometimes showed slow oscillations of the Ca2+-gated K+ current. The characteristics of the Ca2+-activated K+ channels in normal and cancerous mammary cells were quite similar. The slope conductances changed from 8 to 70 pS depending on the mode of recording and the ionic composition in the patch electrode. The open probability of this channel increased between 0.1 to 1 m of the intracellular Ca2+, but it was independent of the membrane potential.Charybdotoxin reduced the activity of the Ca2+-activated K+ channel and the oscillation of the membrane current, but apamin had no apparent effect. The application of tetraethylammonium (TEA) from outside and BaCl2 from inside of the cell diminished the activity of the channel. The properties of this channel were different from those of both the large conductance (BK or MAXI K) and small conductance (SK) type Ca2+-activated K+ channels. 相似文献
4.
Frémont Valérie Blanc Eric Crest Marcel Martin-Eauclaire Marie-France Gola Maurice Darbon Hervé van Rietschoten Jurphaas 《International journal of peptide research and therapeutics》1997,4(4-6):305-312
Summary Ca2+-activated K+ channels consist of a large family of membrane proteins, among which two groups have been characterized by electrophysiological
criteria, the small conductance (SK) and the large conductance (BK) Ca2+-activated K+ channels. Scorpion toxins that block K+ channels exhibit a common three-dimensional structure constituted of a short α-helix connected by disulfide bonds to a β-sheet.
The leiurotoxin I (LTX1) related toxins interact specifically with the SK channel via basic residues of their α-helix, while
the charybdotoxin (ChTX) family recognizes the BK channel with basic residues of their β-sheet. In an attempt to better understand
the structure-activity relationships of these toxins and the characteristics of the electrostatic interactions with the receptor
site, we investigated the electrostatic potential supported by natural toxins and a synthetic analogue to find out if it may
help in understanding the molecular mechanisms involved in this peptide-protein interaction. 相似文献
5.
R. S. Arutyunian S. V. Ivlev N. P. Alekseev 《Journal of Evolutionary Biochemistry and Physiology》2002,38(1):72-78
The effect of various concentrations of Ca+2 and Mg+2 as well as of calcium channel blockers verapamil and nifedipin on impulse activity of frog isolated muscle spindles was studied. Removal of Ca ions from the external Ringer solution was established to increase spontaneous and evoked activity of the muscle spindle. A 4- and 8-fold increase of Ca+2 concentration produces inhibition and complete cessation of the spontaneous and evoked activity in the muscle spindle. Replacement of Ca+2 by Mg+2 is observed to cause no statistically significant change of the spontaneous activity of the isolated muscle spindle; at the same time, at the dynamic spindle extension, the impulse activity rate at the dynamic and static phases of the response rises. Nifedipin and verapamil, blockers of Ca+2 channels, suppress impulse activity both in norm and on the background of increased impulse activity evoked by removal of Ca+2 from the external solution. An increase of muscle spindle impulse activity after the removal of Ca+2 from the external solution is accounted for by transformation of calcium channels of the muscle spindle sensory endings into selective sodium channels. 相似文献
6.
Schmidt EM Münzer P Borst O Kraemer BF Schmid E Urban B Lindemann S Ruth P Gawaz M Lang F 《Biochemical and biophysical research communications》2011,(1):54-60
Platelets have been shown to migrate and thus to invade the vascular wall. Platelet migration is stimulated by SDF-1. In other cell types, migration is dependent on Ca2+ entry via Ca2+ channels. Ca2+ influx is sensitive to cell membrane potential which is maintained by K+ channel activity and/or Cl− channel activity. The present study explored the role of ion channels in the regulation of SDF-1 induced migration. Platelets were isolated from human volunteers as well as from gene targeted mice lacking the Ca2+ activated K+ channel SK4 (sk4−/−) and their wild type littermates (sk4+/+). According to confocal microscopy human platelets expressed the Ca2+ channel Orai1 and the Ca2+-activated K+ channel KCa3.1 (SK4). SDF-1 (100 ng/ml) stimulated migration in human platelets, an effect blunted by Orai1 inhibitors 2-aminoethoxydiphenyl borate 2-APB (10 μM) and SKF-96365 (10 μM), by unspecific K+ channel inhibitor TEA (30 mM), by SK4 specific K+ channel blocker clotrimazole (10 μM), but not by Cl− channel inhibitor 5-nitro-2-(3-phenylpropylamino) benzoic acid NPPB (100 μM). Significant stimulation of migration by SDF-1 was further observed in sk4+/+ platelets but was virtually absent in sk4−/− platelets. In conclusion, platelet migration requires activity of the Ca2+ channel Orai1 and of the Ca2+ activated K+ channel SK4, but not of NPPB-sensitive Cl− channels. 相似文献
7.
We delineated the role of Ca2+-activated K+ channels in the phenomenon of spike frequency adaptation (SFA) exhibited by neurons in the caudal region of nucleus tractus solitarius (cNTS) using intracellular recording coupled with the current-clamp technique in rat brain slices. Intracellular injection of a constant depolarizing current evoked a train of action potentials whose discharge frequency declined rapidly to a lower steady-state level of irregular discharges. This manifested phenomenon of SFA was found to be related to extracellular Ca2+. Low Ca2+ (0.25 mM) or Cd2+ (0.5 mM) in the perfusing medium resulted in a significant increase in the adaptation time constant (adap) and an appreciable reduction in the percentage adaptation of spike frequency (Fadap). In addition, the evoked discharges were converted from an irregular to a regular pattern, accompanied by a profound increase in mean firing rate. Intriguingly, similar alterations in adap, Fadap, discharge pattern and discharge rate were elicited by apamin (1 µM), a selective blocker for small-conductance Ca2+-activated K+ (SK) channels. On the other hand, charybdotoxin (0.1 µM), a selective blocker for large-conductance Ca2+-activated K+ channels, was ineffective. Our results suggest that SK channels of cNTS neurons may subserve the generation of both SFA and irregular discharge patterns displayed by action potentials evoked with a prolonged depolarizing current. 相似文献
8.
Yong-hui Mu Wen-chao Zhao Ping Duan Yun Chen Wei-da Zhao Qian Wang Hui-yin Tu Qian Zhang 《PloS one》2014,9(4)
In cardiomyocytes, Ca2+ entry through voltage-dependent Ca2+ channels (VDCCs) binds to and activates RyR2 channels, resulting in subsequent Ca2+ release from the sarcoplasmic reticulum (SR) and cardiac contraction. Previous research has documented the molecular coupling of small-conductance Ca2+-activated K+ channels (SK channels) to VDCCs in mouse cardiac muscle. Little is known regarding the role of RyRs-sensitive Ca2+ release in the SK channels in cardiac muscle. In this study, using whole-cell patch clamp techniques, we observed that a Ca2+-activated K+ current (IK,Ca) recorded from isolated adult C57B/L mouse atrial myocytes was significantly decreased by ryanodine, an inhibitor of ryanodine receptor type 2 (RyR2), or by the co-application of ryanodine and thapsigargin, an inhibitor of the sarcoplasmic reticulum calcium ATPase (SERCA) (p<0.05, p<0.01, respectively). The activation of RyR2 by caffeine increased the IK,Ca in the cardiac cells (p<0.05, p<0.01, respectively). We further analyzed the effect of RyR2 knockdown on IK,Ca and Ca2+ in isolated adult mouse cardiomyocytes using a whole-cell patch clamp technique and confocal imaging. RyR2 knockdown in mouse atrial cells transduced with lentivirus-mediated small hairpin interference RNA (shRNA) exhibited a significant decrease in IK,Ca (p<0.05) and [Ca2+]i fluorescence intensity (p<0.01). An immunoprecipitated complex of SK2 and RyR2 was identified in native cardiac tissue by co-immunoprecipitation assays. Our findings indicate that RyR2-mediated Ca2+ release is responsible for the activation and modulation of SK channels in cardiac myocytes. 相似文献
9.
Melanoma cells are transformed melanocytes of neural crest origin. K+ channel blockers have been reported to inhibit melanoma cell proliferation. We used whole-cell recording to characterize
ion channels in four different human melanoma cell lines (C8161, C832C, C8146, and SK28). Protocols were used to identify
voltage-gated (KV), Ca2+-activated (KCa), and inwardly rectifying (KIR) K+ channels; swelling-sensitive Cl− channels (Clswell); voltage-gated Ca2+ channels (CaV) and Ca2+ channels activated by depletion of intracellular Ca2+ stores (CRAC); and voltage-gated Na+ channels (NaV). The presence of Ca2+ channels activated by intracellular store depletion was further tested using thapsigargin to elicit a rise in [Ca2+]
i
. The expression of K+ channels varied widely between different cell lines and was also influenced by culture conditions. KIR channels were found in all cell lines, but with varying abundance. Whole-cell conductance levels for KIR differed between C8161 (100 pS/pF) and SK28 (360 pS/pF). KCa channels in C8161 cells were blocked by 10 nm apamin, but were unaffected by charybdotoxin (CTX). KCa channels in C8146 and SK28 cells were sensitive to CTX (K
d
= 4 nm), but were unaffected by apamin. KV channels, found only in C8146 cells, activated at ∼−20 mV and showed use dependence. All melanoma lines tested expressed
CRAC channels and a novel Clswell channel. Clswell current developed at 30 pS/sec when the cells were bathed in 80% Ringer solution, and was strongly outwardly rectifying (4:1
in symmetrical Cl−). We conclude that different melanoma cell lines express a diversity of ion channel types.
Received: 2 April 1996/Revised: 22 August 1996 相似文献
10.
SK2- and KV4.2-containing K+ channels modulate evoked synaptic potentials in CA1 pyramidal neurons. Each is coupled to a distinct Ca2+ source that provides Ca2+-dependent feedback regulation to limit AMPA receptor (AMPAR)- and NMDA receptor (NMDAR)-mediated postsynaptic depolarization. SK2-containing channels are activated by Ca2+ entry through NMDARs, whereas KV4.2-containing channel availability is increased by Ca2+ entry through SNX-482 (SNX) sensitive CaV2.3 R-type Ca2+ channels. Recent studies have challenged the functional coupling between NMDARs and SK2-containing channels, suggesting that synaptic SK2-containing channels are instead activated by Ca2+ entry through R-type Ca2+ channels. Furthermore, SNX has been implicated to have off target affects, which would challenge the proposed coupling between R-type Ca2+ channels and KV4.2-containing K+ channels. To reconcile these conflicting results, we evaluated the effect of SK channel blocker apamin and R-type Ca2+ channel blocker SNX on evoked excitatory postsynaptic potentials (EPSPs) in CA1 pyramidal neurons from CaV2.3 null mice. The results show that in the absence of CaV2.3 channels, apamin application still boosted EPSPs. The boosting effect of CaV2.3 channel blockers on EPSPs observed in neurons from wild type mice was not observed in neurons from CaV2.3 null mice. These data are consistent with a model in which SK2-containing channels are functionally coupled to NMDARs and KV4.2-containing channels to CaV2.3 channels to provide negative feedback regulation of EPSPs in the spines of CA1 pyramidal neurons. 相似文献
11.
Identification of Ether à Go-Go and Calcium-Activated Potassium Channels in Human Melanoma Cells 总被引:1,自引:1,他引:0
R. Meyer R. Schönherr O. Gavrilova-Ruch W. Wohlrab S.H. Heinemann 《The Journal of membrane biology》1999,171(2):107-115
Ion channels and intracellular Ca2+ are thought to be involved in cell proliferation and may play a role in tumor development. We therefore characterized Ca2+-regulated potassium channels in the human melanoma cell lines IGR1, IPC298, and IGR39 using electrophysiological and molecular
biological methods. All cell lines expressed outwardly rectifying K+ channels. Rapidly activating delayed rectifier channels were detected in IGR39 cells. The activation kinetics of voltage-gated
K+ channels in IRG1 and IPC298 cells displayed characteristics of ether à go-go (eag) channels as they were much slower and depended both on the holding potential and on extracellular Mg2+. In addition, they could be blocked by physiological concentrations of intracellular Ca2+. In accordance with these electrophysiological results, analysis of mRNA revealed the expression of a gene coding for h-eag1
channels in IGR1 and IPC298 cells, but not in IGR39 cells. At elevated Ca2+ concentrations various types of Ca2+-activated K+ channels with single-channel characteristics similar to IK and SK channels were detected in IGR1 cells. The whole-cell Ca2+-activated K+ currents were not voltage dependent, insensitive for 100 nm apamin and 200 μm
d-tubocurarine, but were blocked by charybdotoxin (100 nm) and clotrimazole (50 nm). Analysis of mRNA revealed the expression of hSK1, hSK2, and hIK channels in IGR1 cells.
Received: 5 February 1999/Revised: 28 May 1999 相似文献
12.
Use of toxins to study potassium channels 总被引:14,自引:0,他引:14
Maria L. Garcia Antonio Galvez Margarita Garcia-Calvo V. Frank King Jesus Vazquez Gregory J. Kaczorowski 《Journal of bioenergetics and biomembranes》1991,23(4):615-646
Potassium channels comprise groups of diverse proteins which can be distinguished according to each member's biophysical properties. Some types of K+ channels are blocked with high affinity by specific peptidyl toxins. Three toxins, charybdotoxin, iberiotoxin, and noxiustoxin, which display a high degree of homology in their primary amino acid sequences, have been purified to homogeneity from scorpion venom. While charybdotoxin and noxiustoxin are known to inhibit more than one class of channel (i.e., several Ca2+-activated and voltage-dependent K+ channels), iberiotoxin appears to be a selective blocker of the high-conductance, Ca2+-activated K+ channel that is present in muscle and neuroendocrine tissue. A distinct class of small-conductance Ca2+-activated K+ channel is blocked by two other toxins, apamin and leiurotoxin-1, that share no sequence homology with each other. A family of homologous toxins, the dendrotoxins, have been purified from venom of various related species of snakes. These toxins inhibit several inactivating voltage-dependent K+ channels. Although molecular biology approaches have been employed to identify and characterize several species of voltagegated K+ channels, toxins directed against a particular channel can still be useful in defining the physiological role of that channel in a particular tissue. In addition, for those K+ channels which are not yet successfully probed by molecular biology techniques, toxins can be used as biochemical tools with which to purify the target protein of interest. 相似文献
13.
AimsSmall-conductance Ca2 +-activated K+ (SK) channels are recognized as new ion channel candidates in atrial fibrillation (AF), with pivotal implications as novel drug targets due to their atrial-selective distribution in humans. The purpose of this study was to investigate whether SK channels and the Ca2 +-activated K+ current (IK,Ca) are involved in electrical remodeling of human chronic AF (cAF) and whether they display the differential distribution between the right (RA) and left atria (LA).Main methodsThe right (RAA) and left atrial appendage (LAA) myocytes were obtained from 29 sinus rhythm (SR) and 22 cAF patients. The IK,Ca and action potential (AP) were recorded using the patch-clamp technique. Three SK channel subtypes (SK1–3) expressions were assayed by western blot and real-time quantitative PCR analysis.Key findingsThe IK,Ca was decreased and its role in AP repolarization was attenuated in cAF, concomitant with a significant decrease in protein and mRNA levels of SK1 and SK2. In either SR or cAF, there was no difference in the IK,Ca density and protein and mRNA expression levels of SK1–3 between RAA and LAA myocytes.SignificanceOur results demonstrated that SK1 and SK2 are involved in electrical remodeling of cAF. SK1–3 and IK,Ca do not display the inter-atrial differential distribution in SR or cAF. These findings provide a new insight into mechanisms of electrical remodeling of human cAF. 相似文献
14.
《Cell calcium》2018
Ca2+-activated K+ channels (KCa) are expressed at the plasma membrane and in cellular organelles. Expression of all KCa channel subtypes (BK, IK and SK) has been detected at the inner mitochondrial membrane of several cell types. Primary functions of these mitochondrial KCa channels include the regulation of mitochondrial ROS production, maintenance of the mitochondrial membrane potential and preservation of mitochondrial calcium homeostasis. These channels are therefore thought to contribute to cellular protection against oxidative stress through mitochondrial mechanisms of preconditioning. In this review, we summarize the current knowledge on mitochondrial KCa channels, and their role in mitochondrial function in relation to cell death and survival pathways. More specifically, we systematically discuss studies on the role of these mitochondrial KCa channels in pharmacological preconditioning, and according protective effects on ischemic insults to the brain and the heart. 相似文献
15.
Brown A Cornwell T Korniyenko I Solodushko V Bond CT Adelman JP Taylor MS 《American journal of physiology. Cell physiology》2007,292(2):C832-C840
Mechanisms regulating uterine contractility are poorly understood. We hypothesized that a specific isoform of small conductance Ca2+-activated K+ (SK) channel, SK3, promotes feedback regulation of myometrial Ca2+ and hence relaxation of the uterus. To determine the specific functional impact of SK3 channels, we assessed isometric contractions of uterine strips from genetically altered mice (SK3T/T), in which SK3 is overexpressed and can be suppressed by oral administration of doxycycline (SK3T/T+Dox). We found SK3 protein in mouse myometrium, and this expression was substantially higher in SK3T/T mice and lower in SK3T/T+Dox mice compared with wild-type (WT) controls. Sustained contractions elicited by 60 mM KCl were not different among SK3T/T, SK3T/T+Dox, and WT mice. However, the rate of onset and magnitude of spontaneously occurring phasic contractions was muted significantly in isolated uterine strips from SK3T/T mice compared with those from WT mice. These spontaneous contractions were augmented greatly by blockade of SK channels with apamin or by suppression of SK3 expression. Phasic but not tonic contraction in response to oxytocin was depressed in uterine strips from SK3T/T mice, whereas suppression of SK3 channel expression or treatment with apamin promoted the predominance of large coordinated phasic events over tone. Spontaneous contractions and the phasic component of oxytocin contractions were blocked by nifedipine but not by cyclopiazonic acid. Our findings suggest that SK3 channels play an important role in regulating uterine function by limiting influx through L-type Ca2+ channels and disrupting the development of concerted phasic contractile events. uterus; Ca2+-activated K+ channel; doxycycline; mouse 相似文献
16.
Hubert Wiener Dan A. Klaerke Peter L. Jørgensen 《The Journal of membrane biology》1990,117(3):275-283
Summary In the mammalian distal colon, the surface epithelium is responsible for electrolyte absorption, while the crypts are the site of secretion. This study examines the properties of electrical potential-driven86Rb+ fluxes through K+ channels in basolateral membrane vesicles of surface and crypt cells of the rabbit distal colon epithelium. We show that Ba2+-sensitive, Ca2+-activated K+ channels are present in both surface and crypt cell derived vesicles with half-maximal activation at 5×10–7
m free Ca2+. This suggests an important role of cytoplasmic Ca2+ in the regulation of the bidirectional ion fluxes in the colon epithelium.The properties of K+ channels in the surface cell membrane fraction differ from those of the channels in the crypt cell derived membranes. The peptide toxin apamin inhibits Ca2+-activated K+ channels exclusively in surface cell vesicles, while charybdotoxin inhibits predominantely in the crypt cell membrane fraction. Titrations with H+ and tetraethylammonium show that both high-and low-sensitive86Rb+ flux components are present in surface cell vesicles, while the high-sensitive component is absent in the crypt cell membrane fraction. The Ba2+-sensitive, Ca2+-activated K+ channels can be solubilized in CHAPS and reconstituted into phospholipid vesicles. This is an essential step for further characterization of channel properties and for identification of the channel proteins in purification procedures. 相似文献
17.
《Molecular membrane biology》2013,30(2):83-110
Freshly dissociated cells from the stomach muscularis of the toad Bufo marinus have been employed to carry out a systematic set of electrophysiological studies on the membrane properties of smooth muscle. The existence of Ca2+-activated K+ channels became apparent during the first studies under current clamp. In subsequent studies under voltage clamp, a Ca2+-activated, TEA-sensitive outward current was evident, and it was more than an order of magnitude larger than any other current observed in the cells. The channel responsible, at least in part, for this large outward current has been identified on the basis of single-channel records, and some of its main characteristics have been studied. It is similar in many respects to the large-conductance, Ca2+-activated K+ channel seen in other preparations. This channel has now been found in a considerable diversity of smooth muscle types. 相似文献
18.
S.Y. Wang M. Yoshino J.L. Sui M. Wakui P.N. Kao C.Y. Kao 《The Journal of general physiology》1998,112(6):737-756
In freshly dissociated uterine myocytes, the outward current is carried by K+ through channels highly selective for K+. Typically, nonpregnant myocytes have rather noisy K+ currents; half of them also have a fast-inactivating transient outward current (ITO). In contrast, the current records are not noisy in late pregnant myocytes, and ITO densities are low. The whole-cell IK of nonpregnant myocytes respond strongly to changes in [Ca2+]o or changes in [Ca2+]i caused by photolysis of caged Ca2+ compounds, nitr 5 or DM-nitrophene, but that of late-pregnant myocytes respond weakly or not at all. The Ca2+ insensitivity of the latter is present before any exposure to dissociating enzymes. By holding at −80, −40, or 0 mV and digital subtractions, the whole-cell IK of each type of myocyte can be separated into one noninactivating and two inactivating components with half-inactivation at approximately −61 and −22 mV. The noninactivating components, which consist mainly of iberiotoxin-susceptible large-conductance Ca2+-activated K+ currents, are half-activated at 39 mV in nonpregnant myocytes, but at 63 mV in late-pregnant myocytes. In detached membrane patches from the latter, identified 139 pS, Ca2+-sensitive K+ channels also have a half-open probability at 68 mV, and are less sensitive to Ca2+ than similar channels in taenia coli myocytes. Ca2+-activated K+ currents, susceptible to tetraethylammonium, charybdotoxin, and iberiotoxin contribute 30–35% of the total IK in nonpregnant myocytes, but <20% in late-pregnant myocytes. Dendrotoxin-susceptible, small-conductance delayed rectifier currents are not seen in nonpregnant myocytes, but contribute ∼20% of total IK in late-pregnant myocytes. Thus, in late-pregnancy, myometrial excitability is increased by changes in K+ currents that include a suppression of the ITO, a redistribution of IK expression from large-conductance Ca2+-activated channels to smaller-conductance delayed rectifier channels, a lowered Ca2+ sensitivity, and a positive shift of the activation of some large-conductance Ca2+-activated channels. 相似文献
19.
《Channels (Austin, Tex.)》2013,7(1):62-75
Small conductance Ca2+-sensitive potassium (SK2) channels are voltage-independent, Ca2+-activated ion channels that conduct potassium cations and thereby modulate the intrinsic excitability and synaptic transmission of neurons and sensory hair cells. In the cochlea, SK2 channels are functionally coupled to the highly Ca2+ permeant α9/10-nicotinic acetylcholine receptors (nAChRs) at olivocochlear postsynaptic sites. SK2 activation leads to outer hair cell hyperpolarization and frequency-selective suppression of afferent sound transmission. These inhibitory responses are essential for normal regulation of sound sensitivity, frequency selectivity, and suppression of background noise. However, little is known about the molecular interactions of these key functional channels. Here we show that SK2 channels co-precipitate with α9/10-nAChRs and with the actin-binding protein α-actinin-1. SK2 alternative splicing, resulting in a 3 amino acid insertion in the intracellular 3′ terminus, modulates these interactions. Further, relative abundance of the SK2 splice variants changes during developmental stages of synapse maturation in both the avian cochlea and the mammalian forebrain. Using heterologous cell expression to separately study the 2 distinct isoforms, we show that the variants differ in protein interactions and surface expression levels, and that Ca2+ and Ca2+-bound calmodulin differentially regulate their protein interactions. Our findings suggest that the SK2 isoforms may be distinctly modulated by activity-induced Ca2+ influx. Alternative splicing of SK2 may serve as a novel mechanism to differentially regulate the maturation and function of olivocochlear and neuronal synapses. 相似文献
20.
Yasunobu Okada Toshihiho Yada Takako Ohno-Shosaku Shigetoshi Oiki 《The Journal of membrane biology》1987,96(2):121-128
Summary The oscillation of membrane potential in fibroblastic L cells is known to result from periodic stimulation of Ca2+-activated K+ channels due to the oscillatory increase in the intracellular Ca2+ concentration. These repeated hyperpolarizations were inhibited by putative calmodulin antagonists, trifluoperazine (TFP), N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) and promethazine (PMZ), and the concentrations required for half-maximal inhibition were 25, 30 and 300 m, respectively. These doses were lower than those for reducing the membrane resistance due to nonspecific cell damages. Another calmodulin antagonist, chlorpromazine (CPZ), was also effective, but CPZ-sulfoxide was not. Intracellular pressure injections of calmodulin-interacting divalent cations, Ca2+, Sr2+, Mn2+ and Ni2+, elicited slow hyperpolarizations, whereas Mg2+ and Ba2+, which are known to be essentially inert for calmodulin, failed to evoke any responses. The injection of purified calmodulin also brought about a similar hyperpolarization. Quinine, an inhibitor of Ca2+-activated K+ channels, abolished both Ca2+-and calmodulin-induced hyperpolarizations. TFP prevented Ca2+-induced hyperpolarizations. The TFP effect was partially reversed by the calmodulin injection. It is concluded that calmodulin is involved in the operation of Ca2+-activated K+ channels in fibroblasts. 相似文献