共查询到20条相似文献,搜索用时 46 毫秒
1.
Lihui Qu Lei Yu Yanli Wang Xin Jin Qianlong Zhang Ping Lu Xiufeng Yu Weiwei Zhong Xiaodong Zheng Ningren Cui Chun Jiang Daling Zhu 《PloS one》2015,10(12)
Endothelium lines the interior surface of vascular walls and regulates vascular tones. The endothelial cells sense and respond to chemical and mechanical stimuli in the circulation, and couple the stimulus signals to vascular smooth muscles, in which inward rectifier K+ currents (Kir) play an important role. Here we applied several complementary strategies to determine the Kir subunit in primarily cultured pulmonary arterial endothelial cells (PAECs) that was regulated by the Ca2+/calmodulin (CaM)-dependent protein kinase II (CaMKII). In whole-cell voltage clamp, the Kir currents were sensitive to micromolar concentrations of extracellular Ba2+. In excised inside-out patches, an inward rectifier K+ current was observed with single-channel conductance 32.43 ± 0.45 pS and Popen 0.27 ± 0.04, which were consistent with known unitary conductance of Kir 2.1. RT-PCR and western blot results showed that expression of Kir 2.1 was significantly stronger than that of other subtypes in PAECs. Pharmacological analysis of the Kir currents demonstrated that insensitivity to intracellular ATP, pinacidil, glibenclamide, pH, GDP-β-S and choleratoxin suggested that currents weren’t determined by KATP, Kir2.3, Kir2.4 and Kir3.x. The currents were strongly suppressed by exposure to CaMKII inhibitor W-7 and KN-62. The expression of Kir2.1 was inhibited by knocking down CaMKII. Consistently, vasodilation was suppressed by Ba2+, W-7 and KN-62 in isolated and perfused pulmonary arterial rings. These results suggest that the PAECs express an inward rectifier K+ current that is carried dominantly by Kir2.1, and this K+ channel appears to be targeted by CaMKII-dependent intracellular signaling systems. 相似文献
2.
Single inward rectifier K+ channels were studied in Xenopus laevis embryonic myocytes. We have characterized in detail the channel which is most frequently observed (Kir) although we routinely
observe three other smaller current levels with the properties of inward rectifier K+ channels (Kir(0.3), Kir(0.5) and Kir(0.7)). For Kir, slope conductances of inward currents were 10.3, 20.3, and 27.9 pS, in 60, 120 and 200 mM [K+]
o
respectively. Extracellular Ba2+ blocked the normally high channel activity in a concentration-dependent manner (K
A
= 7.8 μm, −90 mV). In whole-cell recordings of inward rectifier K+ current, marked voltage dependence of Ba2+ block over the physiological range of potentials was observed. We also examined current rectification. Following step depolarizations
to voltages positive to E
K
, outward currents through Kir channels were not observed even when the cytoplasmic face of excised patches were exposed to
Mg2+-free solution at pH 9.1. This was probably also true for Kir(0.3), Kir(0.5) and Kir(0.7) channels. We then examined the possibility of modulation of Kir channel activity and found neither ATP nor GTP-γS had any
effect on Kir channel activity when added to the solution perfusing the cytoplasmic face of a patch. Kinetic analysis revealed
Kir channels with a single open state (mean dwell time 72 msec) and two closed states (time constants 1.4, 79 msec). These
results suggest that the native Kir channels of Xenopus myocytes have similar properties to the cloned strong inward rectifier K+ channels, in terms of conductance, kinetics and barium block but does show some differences in the effects of modulators
of channel activity. Furthermore, skeletal muscle may contain either different inward rectifier channels or a single-channel
type which can exist in stable subconductance states.
Received: 16 September 1996/Revised: 14 March 1997 相似文献
3.
《Channels (Austin, Tex.)》2013,7(3):269-279
The inwardly rectifying potassium channel (Kir), Kir4.1 mediates spatial K+-buffering in the CNS. In this process the channel is potentially exposed to a large range of extracellular K+ concentrations ([K+]o). We found that Kir4.1 is regulated by K+o. Increased [K+]o leads to a slow (mins) increase in the whole-cell currents of Xenopus oocytes expressing Kir4.1. Conversely, removing K+ from the bath solution results in a slow decrease of the currents. This regulation is not coupled to the pHi-sensitive gate of the channel, nor does it require the presence of K67, a residue necessary for K+o-dependent regulation of Kir1.1. The voltage-dependent blockers Cs+ and Ba2+ substitute for K+ and prevent deactivation of the channel in the absence of K+o. Cs+ blocks and regulates the channel with similar affinity, consistent with the regulatory sites being in the selectivity-filter of the channel. Although both Rb+ and NH4+ permeate Kir4.1, only Rb+ is able to regulate the channel. We conclude that Kir4.1 is regulated by ions interacting with specific sites in the selectivity filter. Using a kinetic model of the permeation process we show the plausibility of the channel’s sensing the extracellular ionic environment through changes in the selectivity occupancy pattern, and that it is feasible for an ion with the selectivity properties of NH4+ to permeate the channel without inducing these changes. 相似文献
4.
The ligand-sensitive gate of a potassium channel lies close to the selectivity filter 总被引:9,自引:0,他引:9
Potassium channels selectively conduct K+ ions across cell membranes and have key roles in cell excitability. Their opening and closing can be spontaneous or controlled by membrane voltage or ligand binding. We used Ba2+ as a probe to determine the location of the ligand-sensitive gate in an inwardly rectifying K+ channel (Kir6.2). To a K+ channel, Ba2+ and K+ are of similar sizes, but Ba2+ blocks the pore by binding within the selectivity filter. We found that internal Ba2+ could still access its binding site when the channel was shut, which indicates that the ligand-sensitive gate lies above the Ba2+-block site, and thus within or above the selectivity filter. This is in marked contrast to the voltage-dependent gate of KV channels, which is located at the intracellular mouth of the pore. 相似文献
5.
K+ are selectively coordinated in the selectivity filter and concerted K+ and water movements in this region ensure high conduction rates in K+ channels. In channels with long pores many K+ binding sites are located intracellular to the selectivity filter (inner vestibule), but their contribution to permeation has not been well studied. We investigated this phenomenon by slowing the ion permeation process via blocking inwardly rectifying Kir2.1 channels with Ba2+ in the selectivity filter and observing the effect of K+ in the inner vestibule on Ba2+ exit. The dose-response effect of the intracellular K+ concentration ([K+]i) on Ba2+ exit was recorded with and without intracellular polyamines, which compete with K+ for binding sites. Ba2+ exit was facilitated by the cooperative binding of at least three K+. Site-directed mutagenesis studies suggest that K+ interacting with Ba2+ bound in the selectivity filter were located in the region between selectivity filter and cytoplasmic pore, i.e. the water cavity and G-loop. One of the K+ binding sites was located at residue D172 and another was possibly at M301. This study provides functional evidence for the three K+ binding sites in the inner vestibule previously identified by crystal structure study. 相似文献
6.
7.
Members of the eukaryotic PIEZO family (the human orthologs are noted hPIEZO1 and hPIEZO2) form cation-selective mechanically-gated channels. We characterized the selectivity of human PIEZO1 (hPIEZO1) for alkali ions: K+, Na+, Cs+ and Li+; organic cations: TMA and TEA, and divalents: Ba2+, Ca2+, Mg2+ and Mn2+. All monovalent ions permeated the channel. At a membrane potential of -100 mV, Cs+, Na+ and K+ had chord conductances in the range of 35–55 pS with the exception of Li+, which had a significantly lower conductance of ~ 23 pS. The divalents decreased the single-channel permeability of K+, presumably because the divalents permeated slowly and occupied the open channel for a significant fraction of the time. In cell-attached mode, 90 mM extracellular divalents had a conductance for inward currents carried by the divalents of: 25 pS for Ba2+ and 15 pS for Ca2+ at -80 mV and 10 pS for Mg2+ at -50 mV. The organic cations, TMA and TEA, permeated slowly and attenuated K+ currents much like the divalents. As expected, the channel K+ conductance increased with K+ concentration saturating at ~ 45 pS and the KD of K+ for the channel was 32 mM. Pure divalent ion currents were of lower amplitude than those with alkali ions and the channel opening rate was lower in the presence of divalents than in the presence of monovalents. Exposing cells to the actin disrupting reagent cytochalasin D increased the frequency of openings in cell-attached patches probably by reducing mechanoprotection. 相似文献
8.
Robert Bränström Erik Berglund Robin Fröbom Ingo B. Leibiger Barbara Leibiger Craig A. Aspinwall Olof Larsson Per-Olof Berggren 《Biochemistry and Biophysics Reports》2022
BackgroundThe ATP-sensitive K+ (K(ATP)) channel is found in a variety of tissues extending from the heart and vascular smooth muscles to the endocrine pancreas and brain. Common to all K(ATP) channels is the pore-forming subunit Kir6.x, a member of the family of small inwardly rectifying K+ channels, and the regulatory subunit sulfonylurea receptor (SURx). In insulin secreting β-cells in the endocrine part of the pancreas, where the channel is best studied, the K(ATP) channel consists of Kir6.2 and SUR1. Under physiological conditions, the K(ATP) channel current flow is outward at membrane potentials more positive than the K+ equilibrium potential around ?80 mV. However, K(ATP) channel kinetics have been extensively investigated for inward currents and the single-channel kinetic model is based on this type of recording, whereas only a limited amount of work has focused on outward current kinetics.MethodsWe have estimated the kinetic properties of both native and cloned K(ATP) channels under varying ionic gradients and membrane potentials using the patch-clamp technique.ResultsAnalyses of outward currents in K(ATP) and cloned Kir6.2ΔC26 channels, alone or co-expressed with SUR1, show openings that are not grouped in bursts as seen for inward currents. Burst duration for inward current corresponds well to open time for outward current.ConclusionsOutward K(ATP) channel currents are not grouped in bursts regardless of membrane potential, and channel open time for outward currents corresponds to burst duration for inward currents. 相似文献
9.
Ba2+ block of large conductance Ca2+-activated K+ channels was studied in patches of membrane excised from cultures of rat skeletal muscle using the patch clamp technique. Under conditions in which a blocking Ba2+ ion would dissociate to the external solution (150 mM N-methyl-d-glucamine+
o, 500 mM K+
i, 10 μM Ba2+
i, +30 mV, and 100 μM Ca2+
i to fully activate the channel), Ba2+ blocks with a mean duration of ∼2 s occurred, on average, once every ∼100 ms of channel open time. Of these Ba2+ blocks, 78% terminated with a single step in the current to the fully open level and 22% terminated with a transition to a subconductance level at ∼0.26 of the fully open level (preopening) before stepping to the fully open level. Only one apparent preclosing was observed in ∼10,000 Ba2+ blocks. Thus, the preopenings represent Ba2+-induced time-irreversible subconductance gating. The fraction of Ba2+ blocks terminating with a preopening and the duration of preopenings (exponentially distributed, mean = 0.75 ms) appeared independent of changes in [Ba2+]i or membrane potential. The fractional conductance of the preopenings increased from 0.24 at +10 mV to 0.39 at +90 mV. In contrast, the average subconductance level during normal gating in the absence of Ba2+ was independent of membrane potential, suggesting different mechanisms for preopenings and normal subconductance levels. Preopenings were also observed with 10 mM Ba2+
o and no added Ba2+
i. Adding K+, Rb+, or Na+ to the external solution decreased the fraction of Ba2+ blocks with preopenings, with K+ and Rb+ being more effective than Na+. These results are consistent with models in which the blocking Ba2+ ion either induces a preopening gate, and then dissociates to the external solution, or moves to a site located on the external side of the Ba2+ blocking site and acts directly as the preopening gate. 相似文献
10.
Dana Goldoni YouYou Zhao Brian D. Green Barbara J. McDermott Anthony Collins 《Journal of cellular physiology》2010,225(3):751-756
HL‐1 is a line of immortalized cells of cardiomyocyte origin that are a useful complement to native cardiomyocytes in studies of cardiac gene regulation. Several types of ion channel have been identified in these cells, but not the physiologically important inward rectifier K+ channels. Our aim was to identify and characterize inward rectifier K+ channels in HL‐1 cells. External Ba2+ (100 µM) inhibited 44 ± 0.05% (mean ± s.e.m., n = 11) of inward current in whole‐cell patch‐clamp recordings. The reversal potential of the Ba2+‐sensitive current shifted with external [K+] as expected for K+‐selective channels. The slope conductance of the inward Ba2+‐sensitive current increased with external [K+]. The apparent Kd for Ba2+ was voltage dependent, ranging from 15 µM at ?150 mV to 148 µM at ?75 mV in 120 mM external K+. This current was insensitive to 10 µM glybenclamide. A component of whole‐cell current was sensitive to 150 µM 4,4′‐diisothiocyanatostilbene‐2,2′‐disulfonic acid (DIDS), although it did not correspond to the Ba2+‐sensitive component. The effect of external 1 mM Cs+ was similar to that of Ba2+. Polymerase chain reaction using HL‐1 cDNA as template and primers specific for the cardiac inward rectifier Kir2.1 produced a fragment of the expected size that was confirmed to be Kir2.1 by DNA sequencing. In conclusion, HL‐1 cells express a current that is characteristic of cardiac inward rectifier K+ channels, and express Kir2.1 mRNA. This cell line may have use as a system for studying inward rectifier gene regulation in a cardiomyocyte phenotype. J. Cell. Physiol. 225: 751–756, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
11.
Sonya Anderson Tom Brismar Elisabeth Hansson 《Cellular and molecular neurobiology》1995,15(4):439-450
Summary 1. The purpose of this study was (a) to identify if astrocytes show a similar non-Nernstian depolarization in low K+ or low Ca2+ solutions as previously found in human glial and glioma cells, and (b) to analyze the influence of the K+ conductance on the membrane potential of astrocytes.2. The membrane potential (Em) and the ionic conductance were studied with whole-cell patch-clamp technique in neonatal rat astrocytes (5–9 days in culture) and in human glioma cells (U-251MG).3. In 3.0 mM K+, Em was –75 ± 1.0 mV (mean ± SEM,n=39) in rat astrocytes and –79 ± 0.7 mV (n=5) in U-251MG cells. In both cell types Em changed linearly to the logarithm of [K+]0 between 3.0 and 160 mM K+. K+ free medium caused astrocytes to hyperpolarize to –93 ± 2.7 mV (n=21) and U-251MG cells to depolarize to –27 ± 2.1 mV (n=3).4. The I-E curve did not show inward rectification in astrocytes at this developmental stage. The slope conductance (g) exhibited only a small decrease (–19%) in K+ free solution and no significant change in 160 mM K+.5. Ba2+ (1.0 mM) depolarized astrocytes to –45 ± 2.9 mV (n=11), decreasing the slope conductance (g) by 42.4 ± 8.3% (n=11). Ca2+ free solution depolarized astrocytes to –53 ± 3.4 mV (n=12) and resulted in a positive shift of the I-E curve, increasing g by 15.3 ± 8.2% (n=8).6. Calculations indicated that a block of K+ channels explains the depolarizing effect of Ba2+. The effects of K+ free or Ca2+ free solutions on Em can be explained by a transformation of K+ channels to non-specific leakage channels. That astrocytes show a different reaction to low K+ than glioma cells can be related to the lack of inwardly rectifying K+ channels in astrocytes at this developmental stage. 相似文献
12.
《Channels (Austin, Tex.)》2013,7(6):544-550
Neuronal activity results in release of K+ into the extracellular space of the central nervous system. If the excess K+ is allowed to accumulate, neuronal firing will be compromised by the ensuing neuronal membrane depolarization. The surrounding glial cells are involved in clearing K+ from the extracellular space by molecular mechanism(s), the identity of which have been a matter of controversy for over half a century. Kir4.1-mediated spatial buffering of K+ has been promoted as a major contributor to K+ removal although its quantitative and temporal contribution has remained undefined. We discuss the biophysical and experimental challenges regarding determination of the contribution of Kir4.1 to extracellular K+ management during neuronal activity. It is concluded that 1) the geometry of the experimental preparation is crucial for detection of Kir4.1-mediated spatial buffering and 2) Kir4.1 enacts spatial buffering of K+ during but not after neuronal activity. 相似文献
13.
AimsDexmedetomidine is reported to have an effect on peripheral vasoconstriction; however, the exact mechanisms underlying this process are unclear. In this study, we hypothesized that dexmedetomidine-induced inhibition of vascular ATP-sensitive K+ (KATP) channels may be associated with this vasoconstriction. To test this hypothesis, we investigated the effects of dexmedetomidine on vascular KATP-channel activity at the single-channel level.Main methodsWe used cell-attached and inside-out patch-clamp configurations to examine the effects of dexmedetomidine on the activities of native rat vascular KATP channels, recombinant KATP channels with different combinations of various inwardly rectifying potassium channels (Kir6.0 family: Kir6.1, 6.2) and sulfonylurea receptor subunits (SUR1, 2A, 2B), and SUR-deficient channels derived from a truncated isoform of Kir6.2 subunit, namely, Kir6.2ΔC36 channels.Key findingsDexmedetomidine was observed to inhibit the native rat vascular KATP channels in both cell-attached and inside-out configurations. This drug also inhibited the activity of all types of recombinant SUR/Kir6.0 KATP channels as well as Kir6.2ΔC36 channels with equivalent potency.SignificanceThese results indicate that dexmedetomidine directly inhibits KATP channels through the Kir6.0 subunit. 相似文献
14.
Katsumasa Kawahara 《The Journal of membrane biology》1985,88(3):283-292
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
15.
Neuronal activity results in release of K+ into the extracellular space of the central nervous system. If the excess K+ is allowed to accumulate, neuronal firing will be compromised by the ensuing neuronal membrane depolarization. The surrounding glial cells are involved in clearing K+ from the extracellular space by molecular mechanism(s), the identity of which have been a matter of controversy for over half a century. Kir4.1-mediated spatial buffering of K+ has been promoted as a major contributor to K+ removal although its quantitative and temporal contribution has remained undefined. We discuss the biophysical and experimental challenges regarding determination of the contribution of Kir4.1 to extracellular K+ management during neuronal activity. It is concluded that 1) the geometry of the experimental preparation is crucial for detection of Kir4.1-mediated spatial buffering and 2) Kir4.1 enacts spatial buffering of K+ during but not after neuronal activity. 相似文献
16.
Although vasomotion has been considered a feature of the microvascular bed under physiological conditions, it has also been observed following hypotension in several tissues. In this work, 158 mesenteric microvessels of 36 rats were investigated quantitatively in normovolemic and hemorrhaged animals, focussing on diameter changes, particularly vasomotion incidence and characteristics. The femoral arteries of Wistar rats (body weight BW = 188 +/- 23 g, mean +/- SD) anesthetized with pentobarbital were cannulated for arterial pressure (AP) monitoring and blood withdrawal. The protocol consisted of 15 min control and 30 min of hemorrhagic hypotension (AP = 52 +/- 5 mmHg, hemorrhaged vol. = 17 +/- 4 ml/kg BW). During control normovolemic conditions, analysis of mesenteric microcirculation using intravital videomicroscopy revealed neither arteriolar nor venular vasomotion. During hemorrhagic hypotension (HH) microvascular blood flow reduced to 25% of control. While venules did not show diameter changes during HH, arterioles contracted to 85 +/- 20% of control and arteriolar vasomotion appeared in 42% of the animals and 27% of the arterioles. The amplitude of arteriolar diameter change during HH relative to mean diameter and to control diameter averaged 65 +/- 24% (range: 32-129%) and 41 +/- 10% (range: 25-62%), respectively. Vasomotion analysis showed two major frequency components: 1.7 +/- 0.8 and 7.0 +/- 5.2 cycles/min. Arterioles showing vasomotion had a mean control diameter larger than the remaining arterioles and showed the largest constriction during HH. We conclude that hemorrhagic hypotension does not change venular diameter but induces arteriolar constriction and vasomotion in rat mesentery. This activity is expressed as slow waves with high amplitude and fast waves with low amplitude, and is dependent on vessel size. 相似文献
17.
The corpus callosum (CC) is the main white matter tract in the brain and is involved in interhemispheric communication. Using the whole-cell voltage-clamp technique, a study was made of K+-currents in primary cultured astrocytes from the CC of newborn rats. These cells were positive to glial fibrillary acidic protein after culturing in Dulbecco’s Modified Eagle Medium (> 95% of cells) or in serum-free neurobasal medium with G5 supplement (> 99% of cells). Astrocytes cultured in either medium displayed similar voltage-activated ion currents. In 81% of astrocytes, the current had a transient component and a sustained component, which were blocked by 4-aminopyridine and tetraethylammonium, respectively; and both had a reversal potential of ?66 mV, indicating that they were carried by K+ ions. Based on the Ba2+-sensitivity and activation kinetics of the K+-current, two groups of astrocytes were discerned. One group (55% of cells) displayed a strong Ba2+ blockade of the K+-current whose activation kinetics, time course of decay, and the current-voltage relationship were modified by Ba2+. This current was greatly blocked (52%) by Ba2+ in a voltage-dependent way. Another group (45% of cells) presented weak Ba2+-blockade, which was only blocked 24% by Ba2+. The activation kinetics and time course of decay of this current component were unaffected by Ba2+. These results may help to understand better the roles of voltage-activated K+-currents in astrocytes from the rat CC in particular and glial cells in general. 相似文献
18.
The bacterial potassium (K+) channel KcsA provides an attractive model system to study ion permeation behavior in a selective K+-channel. We changed residue at the N-terminal end of the selectivity filter of KcsA (T74V) to its counterpart in inwardly rectifying K+-channels (Kir). The tetramer was found to be stable as unmodified KcsA. Under symmetrical and asymmetrical conditions, Na+ increased the inward current in the virtual absence of K+ however outward currents were nearly abolished which could be recovered upon internal K+ addition. Na+ also drastically increased the channel open time either in the presence or virtual absence of K+. Furthermore, the T74V mutation decreased the internal Ba2+ affinity of the channel possibly by binding to a K+ site in the pore. In additional experiments, another point mutation V76I in T74V mutant was carried out thus the selectivity filter resembled more the selectivity filter of Kir channels. The mutant tetramer was converted into monomers as determined by conventional gel electrophoresis. However, native like gel electrophoresis, Trp fluorescence and acrylamide quenching experiments indicated that this mutant still formed a tetramer and apparently adopted similar folding properties as unmodified KcsA. Single-channel experiments further demonstrated that the channel was selective for K+ over Na+ as Na+ blocked channel currents. These data suggest that single point mutation T74V alters the selectivity filter and allows simultaneous occupancy and conduction of K+ and Na+ probably via ion–ion interaction in the pore. In contrast, both mutations (T74V and V76I) in the same molecule seem to reorganize the pore conformation which controls the overall stability of a selective K+-channel. 相似文献
19.
Membrane potential and ionic currents were studied in cultured rabbit retinal pigment epithelial (RPE) cells using whole-cell patch clamp and perforated-patch recording techniques. RPE cells exhibited both outward and inward voltage-dependent currents and had a mean membrane capacitance of 26±12 pF (sd, n=92). The resting membrane potential averaged ?31±15 mV (n=37), but it was as high as ?60 mV in some cells. When K+ was the principal cation in the recording electrode, depolarization-activated outward currents were apparent in 91% of cells studied. Tail current analysis revealed that the outward currents were primarily K+ selective. The most frequently observed outward K+ current was a voltage- and time-dependent outward current (I K) which resembled the delayed rectifier K+ current described in other cells. I K was blocked by tetraethylammonium ions (TEA) and barium (Ba2+) and reduced by 4-aminopyridine (4-AP). In a few cells (3–4%), depolarization to ?50 mV or more negative potentials evoked an outwardly rectifying K+ current (I Kt) which showed more rapid inactivation at depolarized potentials. Inwardly rectifying K+ current (I KI) was also present in 41% of cells. I KI was blocked by extracellular Ba2+ or Cs+ and exhibited time-dependent decay, due to Na+ blockade, at negative potentials. We conclude that cultured rabbit RPE cells exhibit at least three voltage-dependent K+ currents. The K+ conductances reported here may provide conductive pathways important in maintaining ion and fluid homeostasis in the subretinal space. 相似文献
20.
A.E. Alekseev M.E. Kennedy B. Navarro A. Terzic 《The Journal of membrane biology》1997,159(2):161-168
Co-expression of clones encoding Kir6.2, a K+ inward rectifier, and SUR1, a sulfonylurea receptor, reconstitutes elementary features of ATP-sensitive K+ (KATP) channels. However, the precise kinetic properties of Kir6.2/SUR1 clones remain unknown. Herein, intraburst kinetics of Kir6.2/SUR1
channel activity, heterologously co-expressed in COS cells, displayed mean closed times from 0.7 ± 0.1 to 0.4 ± 0.03 msec,
and from 0.4 ± 0.1 to 2.0 ± 0.2 msec, and mean open times from 1.9 ± 0.4 to 4.5 ± 0.8 msec, and from 12.1 ± 2.4 to 5.0 ± 0.2
msec between −100 and −20 mV, and +20 to +80 mV, respectively. Burst duration for Kir6.2/SUR1 activity was 17.9 ± 1.8 msec
with 5.6 ± 1.5 closings per burst. Burst kinetics of the Kir6.2/SUR1 activity could be fitted by a four-state kinetic model defining transitions between
one open and three closed states with forward and backward rate constants of 1905 ± 77 and 322 ± 27 sec−1 for intraburst, 61.8 ± 6.6 and 23.9 ± 5.8 sec−1 for interburst, 12.4 ± 6.0 and 13.6 ± 2.9 sec−1 for intercluster events, respectively. Intraburst kinetic properties of Kir6.2/SUR1 clones were essentially indistinguishable
from pancreatic or cardiac KATP channel phenotypes, indicating that intraburst kinetics per se were insufficient to classify recombinant Kir6.2/SUR1 amongst native KATP channels. Yet, burst kinetic behavior of Kir6.2/SUR1 although similar to pancreatic, was different from that of cardiac KATP channels. Thus, expression of Kir6.2/SUR1 proteins away from the pancreatic micro-environment, confers the burst kinetic
identity of pancreatic, but not cardiac KATP channels. This study reports the kinetic properties of Kir6.2/SUR1 clones which could serve in the further characterization
of novel KATP channel clones.
Received: 12 March 1997/Revised: 5 May 1997 相似文献