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1.
Summary The effects of cAMP, ATP and GTP on the Ca2+-dependent K+ channel of fresh (1–2 days) or cold-stored (28–36 days) human red cells were studied using atomic absorption flame photometry of Ca2+-EGTA loaded ghosts which had been resealed to monovalent cations in dextran solutions. When high-K+ ghosts were incubated in an isotonic Na+ medium, the rate constant of Ca2+-dependent K+ efflux was reduced by a half on increasing the theophylline concentration to 40mm. This effect was observed in ghosts from both fresh and stored cells, but only if they were previously loaded with ATP. The inhibition was more marked when Mg2+ was added together with ATP, and it was abolished by raising free Ca2+ to the micromolar level. Like theophylline, isobutyl methylxanthine (10mm) also affected K+ efflux. cAMP (0.2–0.5mm), added both internally and externally (as free salt, dibutyryl or bromide derivatives), had no significant effect on K+ loss when the ghost free-Ca2+ level was below 1 m, but it was slightly inhibitory at higher concentrations. The combined presence of cAMP (0.2mm) plus either theophylline (10mm), or isobutyl methylxanthine (0.5mm), was more effective than cAMP alone. This inhibition showed a strict requirement for ATP plus Mg2+ and it, was not overcome by raising internal Ca2+. Ghosts from stored cells seemed more sensitive than those from fresh cells, to the combined action of cAMP and methylxanthines. Loading ATP into ghosts from fresh or stored cells markedly decreased K+ loss. Although this effect was observed in the absence of added Mg2+ (0.5mm EDTA present), it was potentiated upon adding 2mm Mg2+. The K+ efflux from ATP-loaded ghosts was not altered by dithio-bis-nitrobenzoic acid (10mm) or acridine orange (100 m), while it was increased two-to fourfold by incubating with MgF2 (10mm), or MgF2 (10mm)+theophylline (40mm), respectively. By contrast, a marked efflux reduction was obtained by incorporating 0.5mm GTP into ATP-containing ghosts. The degree of phosphorylation obtained by incubating membranes with (-32P)ATP under various conditions affecting K+ channel activity, was in direct correspondence to their effect on K+ efflux. The results suggest that the K+ channel of red cells is under complex metabolic control, via cAMP-mediated and nonmediated mechanisms, some which require ATP and presumably, involve phosphorylation of the channel proteins.  相似文献   

2.
The chlorella virus PBCV-1 was the first virus found to encode a functional potassium channel protein (Kcv). Kcv is small (94 aa) and basically consists of the M1-P-M2 (membrane-pore-membrane) module typical of the pore regions of all known potassium channels. Kcv forms functional channels in three heterologous systems. This brief review discusses the gating, permeability and modulation properties of Kcv and compares them to the properties of bacterial and mammalian K+ channels.  相似文献   

3.
Summary The membrane of mechanically prepared vesicles ofChara corallina has been investigated by patch-clamp techniques. This membrane consists of tonoplast as demonstrated by the measurement of ATP-driven currents directed into the vesicles as well as by the ATP-dependent accumulation of neutral red. Addition of 1mm ATP to the bath medium induced a membrane current of about 3.2 mA·m–2 creating a voltage across the tonoplast of about –7 mV (cytoplasmic side negative). On excised tonoplast patches, currents through single K+-selective channels have been investigated under various ionic conditions. The open-channel currents saturate at large voltage displacements from the equilibrium voltage for K+ with limiting currents of about +15 and –30 pA, respectively, as measured in symmetric 250mm KCl solutions. The channel is virtually impermeable to Na+ and Cl. However, addition of Na+ decreases the K+ currents. TheI–V relationships of the open channel as measured at various K+ concentrations with or without Na+ added are described by a 6-state model, the 12 parameters of which are determined to fit the experimental data.  相似文献   

4.
Summary Using whole-cell patch-clamp techniques, we demonstrate that sheep parotid secretory cells have both inwardly and outwardly rectifying currents. The outwardly rectifying current, which is blocked by 10 mmol/liter tetraethylammonium (TEA) applied extracellularly, is probably carried by the 250 pS Ca2+-and voltage-activated K+ (BK) channel which has been described in previous studies. In contrast, the inwardly rectifying current, which is also carried by K+ ions, is not sensitive to TEA. It is similar to the inwardly rectifying currents observed in many excitable tissues in that (i) its conductance is dependent on the square root of the extracellular K+, (ii) the voltage range over which it is activated is influenced by the extracellular K+ concentration and (iii) it is blocked by the addition of Cs+ ions (670 µmol/liter) to the bathing solution. Our previously published cell-attached patch studies have shown that the channel type most commonly observed in the basolateral membrane of unstimulated sheep parotid secretory cells is a K+ channel with a conductance of 30 pS and, in this study, we find that its conductance also depends on the square root of the extracellular K+ concentration. It thus seems likely that it carries the inwardly rectifying K+ current seen in the whole-cell studies.  相似文献   

5.
In the present study, we describe the existence of mitochondrial ATP-dependent K+ channel (mitoKATP) in two different insect tissues, fat body and muscle of cockroach Gromphadorhina coquereliana. We found that pharmacological substances known to modulate potassium channel activity influenced mitochondrial resting respiration. In isolated mitochondria oxygen consumption increased by about 13% in the presence of potassium channel openers (KCOs) such as diazoxide and pinacidil. The opening of mitoKATP was reversed by glibenclamide (potassium channel blocker) and 1 mM ATP. Immunological studies with antibodies raised against the Kir6.1 and SUR1 subunits of the mammalian ATP-sensitive potassium channel, indicated the existence of mitoKATP in insect mitochondria. MitoKATP activation by KCOs resulted in a decrease in superoxide anion production, suggesting that protection against mitochondrial oxidative stress may be a physiological role of mitochondrial ATP-sensitive potassium channel in insects.  相似文献   

6.
Huang CC  Hall AC  Lim PH 《Life sciences》2004,75(3):329-338
The agent hemin has been demonstrated to be able to initiate a coordinated differentiation program in several cell types. In the present study, we examined the ability of hemin on inducing cell differentiation and Ca(2+)-activated K(+) channel activity in erythroleukemic K562 cells. Treating undifferentiated K562 cells with hemin (0.1 mM) for five days caused these cells to display differentiation-like characteristics including chromatin aggregation, nuclear degradation, pseudopod extension of the membrane and increased hemoglobin production. However, overall cell viability was not significantly changed by the presence of hemin. After hemin treatment for different periods, the Ca(2+)-activated K(+) channel was activated by the addition of ionomycin (1 microM), and was inhibited by either clotrimazole, charybdotoxin, or EGTA. Before hemin treatment there was no significant Ca(2+)-activated K(+) channel activity present in undifferentiated K562 cells. After hemin treatment for 5 days, a significant Ca(2+)-activated K(+) channel activity was detected. This increasing Ca(2+)-activated K(+) channel activity may be contributed from a subtype of Ca(2+)-activated K(+) channel, KCNN4. These results suggest that the ability of hemin to induce increasing Ca(2+)-activated K(+) channel activity may contribute to the mechanism of hemin-induced K562 cell differentiation.  相似文献   

7.
The influence of cytochalasin B (CB), a potent inhibitor of cytoplasmic streaming, on 86Rb-labelled K+ translocation by detopped Lycopersicon esculentum Mill., Cucumis sativus L. and Zea mays L. plants was examined by measuring the radioactivity in xylem exudate before and after the addition of CB to the medium bathing the roots. CB caused complete cessation of cytoplasmic streaming in root segments within 15 min but was without effect on either total 86Rb uptake or exudation. Thus factors other than cytoplasmic streaming limit the movement of K+ across the symplast of the root of higher plants.  相似文献   

8.
Two classes of small homologous basic proteins, mamba snake dendrotoxins (DTX) and bovine pancreatic trypsin inhibitor (BPTI), block the large conductance Ca2+-activated K+ channel (BKCa, KCa1.1) by production of discrete subconductance events when added to the intracellular side of the membrane. This toxin-channel interaction is unlikely to be pharmacologically relevant to the action of mamba venom, but as a fortuitous ligand-protein interaction, it has certain biophysical implications for the mechanism of BKCa channel gating. In this work we examined the subconductance behavior of 9 natural dendrotoxin homologs and 6 charge neutralization mutants of δ-dendrotoxin in the context of current structural information on the intracellular gating ring domain of the BKCa channel. Calculation of an electrostatic surface map of the BKCa gating ring based on the Poisson-Boltzmann equation reveals a predominantly electronegative surface due to an abundance of solvent-accessible side chains of negatively charged amino acids. Available structure-activity information suggests that cationic DTX/BPTI molecules bind by electrostatic attraction to site(s) on the gating ring located in or near the cytoplasmic side portals where the inactivation ball peptide of the β2 subunit enters to block the channel. Such an interaction may decrease the apparent unitary conductance by altering the dynamic balance of open versus closed states of BKCa channel activation gating.  相似文献   

9.
Transient outward K+ current (Ito) plays a crucial role in the early phase of cardiac action potential repolarization. Kv4.3 K+ channel is an important component of Ito. The function and expression of Kv4.3 K+ channel decrease in variety of heart diseases, especially in heart hypertrophy/heart failure. In this review, we summarized the changes of cardiac Kv4.3 K+ channel in heart diseases and discussed the potential role of Kv4.3 K+ channel in heart hypertrophy/heart failure. In heart hypertrophy/heart failure of mice and rats, downregulation of Kv4.3 K+ channel leads to prolongation of action potential duration (APD), which is associated with increased [Ca2+]i, activation of calcineurin and heart hypertrophy/heart failure. However, in canine and human, Kv4.3 K+ channel does not play a major role in setting cardiac APD. So, in addition to Kv4.3 K+ channel/APD/[Ca2+]i pathway, there exits another mechanism of Kv4.3 K+ channel in heart hypertrophy and heart failure: downregulation of Kv4.3 K+ channels leads to CaMKII dissociation from Kv4.3–CaMKII complex and subsequent activation of the dissociated CaMKII, which induces heart hypertrophy/heart failure. Upregulation of Kv4.3 K+ channel inhibits CaMKII activation and its related harmful consequences. We put forward a new point-of-view that Kv4.3 K+ channel is involved in heart hypertrophy/heart failure independently of its electric function, and drugs inhibiting or upregulating Kv4.3 K+ channel might be potentially harmful or beneficial to hearts through CaMKII.  相似文献   

10.
Transient outward K+ current (Ito) plays a crucial role in the early phase of cardiac action potential repolarization. Kv4.3 K+ channel is an important component of Ito. The function and expression of Kv4.3 K+ channel decrease in variety of heart diseases, especially in heart hypertrophy/heart failure. In this review, we summarized the changes of cardiac Kv4.3 K+ channel in heart diseases and discussed the potential role of Kv4.3 K+ channel in heart hypertrophy/heart failure. In heart hypertrophy/heart failure of mice and rats, downregulation of Kv4.3 K+ channel leads to prolongation of action potential duration (APD), which is associated with increased [Ca2+]i, activation of calcineurin and heart hypertrophy/heart failure. However, in canine and human, Kv4.3 K+ channel does not play a major role in setting cardiac APD. So, in addition to Kv4.3 K+ channel/APD/[Ca2+]i pathway, there exits another mechanism of Kv4.3 K+ channel in heart hypertrophy and heart failure: downregulation of Kv4.3 K+ channels leads to CaMKII dissociation from Kv4.3–CaMKII complex and subsequent activation of the dissociated CaMKII, which induces heart hypertrophy/heart failure. Upregulation of Kv4.3 K+ channel inhibits CaMKII activation and its related harmful consequences. We put forward a new point-of-view that Kv4.3 K+ channel is involved in heart hypertrophy/heart failure independently of its electric function, and drugs inhibiting or upregulating Kv4.3 K+ channel might be potentially harmful or beneficial to hearts through CaMKII.  相似文献   

11.
(i) Effects of veratridine on ionic conductances of human peripheral blood T lymphocytes have been investigated using the whole-cell patch-clamp technique, (ii) Veratridine reduces the net outward current evoked by membrane depolarizations. The reduction originates from block of a 4-aminopyridine-sensitive, voltage-gated K+ current, (iii) Human T lymphocytes do not appear to express voltage-gated Na+ channels, since inward currents are observed neither in control nor in veratridine- and bretylium-exposed lymphocytes. (iv) The effect of veratridine consists of an increase in the rate of decay of the voltage-gated K+ current and a reduction of the peak current amplitude. Both effects depend on veratridine concentration. Halfmaximum block occurs at 97 m and the time constant of decay is reduced by 50% at 54 m of veratridine. (v) Possible mechanisms of veratridine action are discussed. The increased rate of K+ current decay is most likely due to open channel block. The decrease of current amplitude may involve an additional mechanism. (vi) In cultured mouse neuroblastoma N1E-115 cells, veratridine blocks a component of voltage-gated K+ current, in addition to its effect on voltage-gated Na+ current. This result shows that the novel effect of veratridine is not confined to lymphocytes.We thank Jacobien Künzel of the Wilhelmina Hospital for Children, Utrecht, for providing the blood samples and Aart de Groot for technical assistance. The research was supported by a fellowship of the Royal Netherlands Academy of Arts and Sciences to M. Oortgiesen.  相似文献   

12.
Summary Chronic exposure to high potassium stimulates K+-secretory mechanisms in the diluting segment of the amphibian kidney (K+ adaptation). Since K+ net flux depends critically on the passive cell membrane permeabilities for K+ ions, cable analysis and K+-concentration step changes were applied in this nephron segment to assess the individual resistances of the epithelium and the K+ conductance of the luminal cell membrane. Experiments were performed in the isolated, doubly-perfused kidney of both control and K+-adaptedAmphiuma. In control animals transepithelial resistance was 290±27 cm2, which decreased significantly to 199±17 cm2 after K+ adaptation. The resistance in parallel of the luminal and peritubular cell membrane decreased from a control value of 157±14 to 108±6 cm2 after chronic K+ treatment. This was paralleled by a decrease of the ratio of the luminal to peritubular cell membrane resistance from 2.5±0.1 to 1.9±0.1, respectively. Estimation of the individual cell membrane resistances reveals that the combined resistance of the luminal and peritubular cell membrane is in the same order of magnitude as the paracellular shunt resistance in diluting segments of both control and K+-adapted animals. The luminal cell membrane is K+ selective under both conditions, but the absolute luminal K+ conductance increases by some 60% with K+ adaptation. This leads to an increased back-leak of K+ from cell to lumen and may explain stimulated K+ net secretion found after chronic K+ loading.  相似文献   

13.
Two K+ ATP channel blockers, 5-hydroxydecanoate (5-HD) and glyburide, are often used to study cross-talk between Na+/K+-ATPase and these channels. The aim of this work was to characterize the effects of these blockers on purified Na+/K+-ATPase as an aid to appropriate use of these drugs in studies on this cross-talk. In contrast to known dual effects (activating and inhibitory) of other fatty acids on Na+/K+-ATPase, 5-HD only inhibited the enzyme at concentrations exceeding those that block mitochondrial K+ ATP channels. 5-HD did not affect the ouabain sensitivity of Na+/K+-ATPase. Glyburide had both activating and inhibitory effects on Na+/K+-ATPase at concentrations used to block plasma membrane K+ ATP channels. The findings justify the use of 5-HD as specific mitochondrial channel blocker in studies on the relation of this channel to Na+/K+-ATPase, but question the use of glyburide as a specific blocker of plasma membrane K+ ATP channels, when the relation of this channel to Na+/K+-ATPase is being studied.  相似文献   

14.
The pH-sensitivity of transepithelial K+ transport was studied in vitro in isolated vestibular dark cell epithelium from the gerbil ampulla. The cytosolic pH (pH iwas measured microfluorometrically with the pH-sensitive dye 2,7-bicarboxyethyl-5(6)-carboxyfluorescein (BCECF) and the equivalent short-circuit current (I sc), which is a measure for transepithelial K+ secretion, was calculated from measurements of the transepithelial voltage (V t)and the transepithelial resistance (R t) in a micro-Ussing chamber. All experiments were conducted in virtually HCO 3 -free solutions. Under control conditions, pH iwas 7.01±0.04 (n=18), V twas 9.1±0.5 mV, R t16.7±0.09 cm2, and I sc was 587±30 A/cm2 (n=49). Addition of 20 mm propionate caused a biphasic effect involving an initial acidification of pH i, increase in V tand I sc and decrease in R tand a subsequent alkalinization of pH i, decrease of V tand increase of R t. Removal of propionate caused a transient effect involving an alkalinization of pH i, a decrease of V tand I sc and an increase in R t. pH iin the presence of propionate exceeded pH iunder control conditions. Effects of propionate on V t, R tand I sc were significantly larger when propionate was applied to the basolateral side rather than to the apical side of the epithelium. The pH i-sensitivityof I sc between pH 6.8 and 7.5 was –1089 A/(cm2 · pH-unit) suggesting that K+ secretion ceases at about pH i7.6. Acidification of the extracellular pH (pH o)caused an increase of V tand I sc and a decrease of R tmost likely due to acidification of pH i. Effects were significantly larger when the extracellular acidification was applied to the basolateral side rather than to the apical side of the epithelium. The pH osensitivity of I sc between pH 7.4 and 6.4 was –155 A/(cm2 · pH unit). These results demonstrate that transepithelial K+ transport is sensitive to pH iand pH oand that vestibular dark cells contain propionate uptake mechanism. Further, the data suggest that cytosolic acidification activates and that cytosolic alkalinization inactivates the slowly activating K+ channel (I sK)in the apical membrane. Whether the effect of pH ion the I sK channel is a direct or indirect effect remains to be determined.The authors wish to thank Drs. Daniel C. Marcus, Zhjiun Shen and Hiroshi Sunose for helpful discussions. This work was supported by grants NIH-R29-DC01098 and NIH-R01-DC00212.  相似文献   

15.

Background

Cigarette smoke is a major risk factor for chronic obstructive pulmonary disease (COPD), an inflammatory lung disorder. COPD is characterized by an increase in CD8+ T cells within the central and peripheral airways. We hypothesized that the CD8+ T cells in COPD patients have increased Toll-like receptor (TLR) expression compared to control subjects due to the exposure of cigarette smoke in the airways.

Methods

Endobronchial biopsies and peripheral blood were obtained from COPD patients and control subjects. TLR4 and TLR9 expression was assessed by immunostaining of lung tissue and flow cytometry of the peripheral blood. CD8+ T cells isolated from peripheral blood were treated with or without cigarette smoke condensate (CSC) as well as TLR4 and TLR9 inhibitors. PCR and western blotting were used to determine TLR4 and TLR9 expression, while cytokine secretion from these cells was detected using electrochemiluminescence technology.

Results

No difference was observed in the overall expression of TLR4 and TLR9 in the lung tissue and peripheral blood of COPD patients compared to control subjects. However, COPD patients had increased TLR4 and TLR9 expression on lung CD8+ T cells. Exposure of CD8+ T cells to CSC resulted in an increase of TLR4 and TLR9 protein expression. CSC exposure also caused the activation of CD8+ T cells, resulting in the production of IL-1β, IL-6, IL-10, IL-12p70, TNFα and IFNγ. Furthermore, inhibition of TLR4 or TLR9 significantly attenuated the production of TNFα and IL-10.

Conclusions

Our results demonstrate increased expression of TLR4 and TLR9 on lung CD8+ T cells in COPD. CD8+ T cells exposed to CSC increased TLR4 and TLR9 levels and increased cytokine production. These results provide a new perspective on the role of CD8+ T cells in COPD.  相似文献   

16.
Large-conductance Ca2+-dependent K+ (BKCa) channels are activated by intracellular Ca2+ and membrane depolarization in an allosteric manner. We investigated the pharmacological and biophysical characteristics of a BKCa-type K+ channel in androgen-dependent LNCaP (lymph node carcinoma of the prostate) cells with novel functional properties, here termed BKL. K+ selectivity, high conductance, activation by Mg2+ or NS1619, and inhibition by paxilline and penitrem A largely resembled the properties of recombinant BKCa channels. However, unlike conventional BKCa channels, BKL channels activated in the absence of free cytosolic Ca2+ at physiological membrane potentials; the half-maximal activation voltage was shifted by about −100 mV compared with BKCa channels. Half-maximal Ca2+-dependent activation was observed at 0.4 μM for BKL (at −20 mV) and at 4.1 μM for BKCa channels (at +50 mV). Heterologous expression of hSlo1 in LNCaP cells increased the BKL conductance. Expression of hSlo-β1 in LNCaP cells shifted voltage-dependent activation to values between that of BKL and BKCa channels and reduced the slope of the Popen (open probability)-voltage curve. We propose that LNCaP cells harbor a so far unknown type of BKCa subunit, which is responsible for the BKL phenotype in a dominant manner. BKL-like channels are also expressed in the human breast cancer cell line T47D. In addition, functional expression of BKL in LNCaP cells is regulated by serum-derived factors, however not by androgens.  相似文献   

17.
The Kv1.3 channel inactivates via the P/C-type mechanism, which is influenced by a histidine residue in the pore region (H399, equivalent of Shaker 449). Previously we showed that the electric field of the protonated histidines at low extracellular pH (pHe) creates a potential barrier for K+ ions just outside the pore that hinders their exit from the binding site controlling inactivation (control site) thereby slowing inactivation kinetics. Here we examined the effects of extracellular potassium [K+]e and pHe on the rate of inactivation of Kv1.3 using whole-cell patch-clamp. We found that in 150 mM [K+]e inactivation was accelerated upon switching to pHe 5.5 as opposed to the slowing at 5 mM [K+]e. The transition from slowing to acceleration occurred at 40 mM [K+]e, whereas this "turning point" was at 20 mM [K+]e for inward currents. The rate of entry of Ba(2+) ions from the extracellular space to the control site was significantly slowed by low pHe in wild-type hKv1.3, but it was insensitive to pH(e) in H399K and H399L mutants. Based on these observations we expanded our model and propose that the potential barrier created by the protonated histidines impedes the passage of K+ ions between the extracellular medium and the control site in both directions and the effect on inactivation rate (acceleration or slowing) depends on the relative contribution of filling from the extracellular and intracellular sides.  相似文献   

18.
Nonesterified long-chain fatty acids (myristic, palmitic, oleic and arachidonic), added at low amounts (around 20 nmol/mg protein) to rat liver mitochondria, energized by respiratory substrates and suspended in isotonic solutions of KCl, NaCl, RbCl or CsCl, adjusted to pH 8.0, induce a large-scale swelling followed by a spontaneous contraction. Such swelling does not occur in alkaline solutions of choline chloride or potassium gluconate or sucrose. These changes in the matrix volume reflect a net uptake, followed by net extrusion, of KCl (or another alkali metal chloride) and are characterized by the following features: (1) Lowering of medium pH from 8.0 to 7.2 results in a disappearance of the swelling-contraction reaction. (2) The contraction phase disappears when the respiration is blocked by antimycin A. (3) Quinine, an inhibitor of the K+/H+ antiporter, does not affect swelling but suppresses the contraction phase. (4) The swelling phase is accompanied by a decrease of the transmembrane potential and an increase of respiration, whereas the contraction is followed by an increase of the membrane potential and a decrease of oxygen uptake. (5) Nigericin, a catalyst of the K+/H+ exchange, prevents or partly reverses the swelling and partly restores the depressed membrane potential. These results indicate that long-chain fatty acids activate in liver mitochondria suspended in alkaline saline media the uniporter of monovalent alkali metal cations, the K+/H+ antiporter and the inner membrane anion channel. These effects are presumably related to depletion of mitochondrial Mg2+, as reported previously [Arch. Biochem. Biophys. 403 (2002) 16], and are responsible for the energy-dissipating K+ cycling. The uniporter and the K+/H+ antiporter are in different ways activated by membrane stretching and/or unfolding, resulting in swelling followed by contraction.  相似文献   

19.
Summary The apical membrane K+ permeability of the newt proximal tubular cells was examined in the doubly perfused isolated kidney by measuring the apical membrane potential change (V a change) during alteration of luminal K+ concentration and resultant voltage deflections caused by current pulse injection into the lumen.V a change/decade for K+ was 50 mV at K+ concentration higher than 25mm, and the resistance of the apical membrane decreased bt 58% of control when luminal K+ concentration was increased from 2.5 to 25mm. Ba2+ (1mm in the lumen) reducedV a change/decade to 24 mV and increased the apical membrane resistance by 70%. These data support the view that Ba2+-sensitive K+ conductance exists in the apical membrane of the newt proximal tubule. Furthermore, intracellular K+ activity measured by K+-selective electrode was 82.4 ± 3.6 meq/liter, which was higher than that predicted from the Nernst equation for K+ across both cell membranes. Thus, it is concluded that cell K+ passively diffuses, at least in part, through the K+ conductive pathway of the apical membrane.  相似文献   

20.
The mechanism of blockade of the delayed rectifier potassium ion channel in squid giant axons by intracellular quaternary ammonium ions (QA) appears to be remarkably sensitive to the structure of the blocker. TEA, propyltriethyl-ammonium (C3), and propyltetraethylammonium (TAA-C3) all fail to alter the deactivation, or tail current time course following membrane depolarization, even with relatively large concentrations of the blockers, whereas butyltriethylammonium (C4), butyltetraethylammonium (TAA-C4), and pentytriethyammonium (C5) clearly do have such an effect. The relative electrical distance of blockade for all of these ions is 0.25–0.3 from the inner surface of the membrane. The observations concerning TEA, C3, and TAAC3 suggest that these ions can block the channel in either its open or its closed state. The results with C4, TAA-C4, and C5 are consistent with the open channel block model. Moreover, the sensitivity of block mechanism to the structure of the blocker suggests that the gate is located close to the QA ion binding site and that TEA, C3, and TAA-C3 do not interfere with channel gating, whereas C4, TAA-C4, C5, and ions having a longer hydrophobic tail than C5 do have such an effect. The parameters of block obtained for all QA ions investigated were unaffected by changes in the extracellular potassium ion concentration.The author gratefully acknowledges Paul Guth of Cambridge Chemical for custom synthesis of the C n compounds used in this study, Michael Rogawski for helpful discussion of this work, and Adam Sherman of Alembic Software and Vijay Kowtha for technical assistance in data acquisition and analysis.  相似文献   

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