共查询到20条相似文献,搜索用时 31 毫秒
1.
Melanie E. M. Kelly S. Jeffrey Dixon Stephen M. Sims 《The Journal of membrane biology》1992,126(2):171-181
Summary Ionic conductances of rabbit osteoclasts were investigated using both whole-cell and cell-attached configurations of the patch-clamp recording technique. The predominant conductance found in these cells was an inwardly rectifying K+ conductance. Whole-cell currents showed an N-shaped current-voltage (I–13;V) relation with inward current activated at potentials negative to EK. When external K+ was varied, I-V curves shifted 53 mV/10-fold change in [K+]out, as predicted for a K+-selective channel. Inward current was blocked by Ba2+ and showed a time-dependent decline at negative potentials, which was reduced in Na+-free external solution. Inward single-channel currents were recorded in the cell-attached configuration. Single-channel currents were identified as inward-rectifier K+ channels based on the following observations: (i) Unitary I-V relations rectified, with only inward current resolved. (ii) Unitary conductance () was 31 pS when recorded in the cell-attached configuration with 140 mm K+ in the pipette and was found to be dependent on [K+]. (iii) Addition of Ba2+ to the pipette solution abolished single-channel events. We conclude that rabbit osteoclasts possess inwardly rectifying K+ channels which give rise to the inward current recorded at negative potentials in the whole-cell configuration. This inwardly rectifying K+ current may be responsible for setting the resting membrane potential and for dissipating electrical potential differences which arise from electrogenic transport of protons across the osteoclast ruffled border.This work was supported by The Arthritis Society and the Medical Research Council of Canada. M.E.M.K. was supported by a fellowship, S.J.D. a development Grant and S.M.S. a scholarship from the Medical Research Council. We thank Dr. Zu Gang Zheng for help with scanning microscopy. 相似文献
2.
Ira R. Josephson 《Molecular and cellular biochemistry》1989,80(1-2):21-26
Summary The voltage- and time-dependent properties of whole-cell, multi-channel (outside-out), and single channel inwardly-rectifying K+ currents were studied using adult and neonatal rat, and embryonic chick ventricular myocytes. Inward rectification of the current-voltage relationship was found in the whole-cell and single channel measurements. The steady-state single channel probability of opening decreased with hyperpolarization from EK, as did the mean open time, thereby explaining the time-dependent inactivation of the macroscopic current. Myocytes dialysed with a Mg++-free K+ solution (to remove the property of inward rectification) displayed a quasi-linear current-voltage relationship. The outward K+ currents flowing through the modified inward rectifier channels were able to be blocked by the local anesthetic and anti-arrhythmic agent, lidocaine. 相似文献
3.
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
4.
During resorption of mineralized tissues, osteoclasts are exposed to marked changes in the concentration of extracellular Ca2+ and H+. We examined the effects of these cations on two types of K+ currents previously described in these cells. Whole-cell patch clamp recordings of membrane currents were made from osteoclasts freshly isolated from neonatal rats. In control saline (1 mm Ca2+, pH 7.4), the voltage-gated, outwardly rectifying K+ current activates at approximately 45 mV and the conductance is half-maximally activated at –29 mV (V
0.5). Increasing [Ca2+]out rapidly and reversibly shifted the current-voltage (I–V) relation to more positive potentials. Current at –29 mV decreased to 28 and 9% of control current at 5 and 10 mm [Ca2+]out, respectively. This effect of elevating [Ca2+]out was due to a positive shift of the K+ channel voltage activation range. Zn2+ or Ni2+ (5 to 500 m) also shifted the I–V relation to more positive potentials and had additional effects consistent with blockade of the K+ channel. Based on the extent to which these divalent cations affected the voltage activation range of the outwardly rectifying K+ current, the potency sequence was Zn2+ > Ni2+ > Ca2+. Lowering or raising extracellular pH also caused shifts of the voltage activation range to more positive or negative potentials, respectively. In contrast to their effects on the outwardly rectifying K+ current, changes in the concentration of extracellular H+ or Ca2+ did not shift the voltage activation range of the inwardly rectifying K+ current. These findings are consistent with Ca2+ and other cations affecting voltage-dependent gating of the osteoclast outwardly rectifying K+ channel through changes in surface charge.This work was supported by The Arthritis Society and the Medical Research Council of Canada. S.M.S. is supported by a Scientist Award and S.J.D. by a Development Grant from the Medical Research Council. 相似文献
5.
Summary Whole-cell sealed-on pipettes have been used to measure electrical properties of the plasmalemma surrounding protoplasts isolated from Black Mexican sweet corn shoot cells from suspension culture. In these protoplasts the membrane resting potential (V
m
) was found to be –59±23 mV (n=23) in 1mm K
o
–
. The meanV
m
became more negative as [K–]
o
decreased, but was more positive than the K+ equilibrium potential. There was no evidence of electrogenic pump activity. We describe four features of the current-voltage characteristic of the plasmalemma of these protoplasts which show voltagegated channel activity. Depolarization of the whole-cell membrane from the resting potential activates time- and voltage-dependent outward current through K+-selective channels. A local minimum in the outward current-voltage curve nearV
m
=150 mV suggests that these currents are mediated by two populations of K+-selective channels. The absence of this minimum in the presence of verapamil suggests that the activation of one channel population depends on the influx of Ca2+ into the cytoplasm. We identify unitary currents from two K+-selective channel populations (40 and 125 pS) which open when the membrane is depolarized; it is possible that these mediate the outward whole-cell current. Hyperpolarization of the membrane from the resting potential produces time- and voltage-dependent inward whole-cell current. Current activation is fast and follows an exponential time course. The current saturates and in some cases decreases at membrane potentials more negative than –175 mV. This current is conducted by poorly selective K+ channels, whereP
Cl/P
K=0.43±0.15. We describe a low conductance (20 pS) channel population of unknown selectivity which opens when the membrane is hyperpolarized. It is possible that these channels mediate inward whole-cell current. When the membrane is hyperpolarized to potentials more negative than –250 mV large, irregular inward current is activated. A third type of inward whole-cell current is briefly described. This activates slowly and with a U-shaped current-voltage curve over the range of membrane potentials –90<V
m
<0 mV. 相似文献
6.
Mark Tester 《The Journal of membrane biology》1988,105(1):77-85
Summary The outer membranes of plant cells contain channels which are highly selective for K+. In the giant-celled green algaChara corallina, K+ currents in the plasmalemma were measured during the action potential and when the cell was depolarized to the K+ equilibrium potential in high external K+ concentrations. Currents in both conditions were reduced by externally added tetraethylammonium (TEA+), Ba2+, Na+ and Cs+. In contrast to inhibition by TEA+, the latter three ions inhibited inward K+ current in a voltage-dependent manner, and reduced inward current more than outward. Ba2+ and Na+ also appeared to inhibit outward current in a strongly voltage-dependent manner. The blockade by Cs+ is studied in more detail in the following paper. TEA+ inhibited both inward and outward currents in a largely voltage-independent manner, with an apparentK
D
of about 0.7 to 1.1mm, increasing with increasing external K+. All inhibitors reduced current towards a similar linear leak, suggesting an insensitivity of the background leak inChara to these various K+ channel inhibitors. The selectivity of the channel to various monovalent cations varied depending on the method of measurement, suggesting that ion movement through the K+-selective channel may not be independent. 相似文献
7.
Outward and inward currents, mainly carried by K+, were detected in protoplasts of pollen grains (PG) and pollen tubes (PT) of Lilium longiflorum Thunb. by using the whole-cell configuration of the patch-clamp technique. The outward K+ current (IK+
out) was similar in both protoplast types, while the inward K+ current (IK+
in) was higher in pollen tube protoplasts. In PT but not in PG protoplasts, inward K+ currents were already detectable at negative membrane voltages usually monitored in lily pollen. IK+
in consisted of a slow and a fast current component, as revealed by fitting a sum of two exponential functions to the time-dependent current. The contribution of the fast component to the total inward current was higher in PT than in PG protoplasts, which was even more evident at acidic pH of the external medium. Therefore, based on the measured characteristics, the IK+
in of PT protoplasts may contribute to the endogenous K+ currents surrounding a growing pollen tube.
Abbreviations: BS, bath solution; BTP, bis-Tris-propane; MES, 2-N-morpholinoethane sulfonic acid; Vact, activation voltage; VM, membrane voltage; Erev, reversal potential; IK+
in, inward K+ current; IK+
out, outward K+ current; PG, pollen grain; PT, pollen tube; PM, pipette medium 相似文献
8.
Xylem parenchyma cells are situated around the (apoplastic) xylem vessels and are involved in the control of the composition of the xylem sap by exporting and resorbing solutes. We investigated properties of the K+ inward rectifier in the plasma membrane of these cells by performing patch clamp experiments on protoplasts in the whole-cell configuration. Inward currents were sensitive to the K+ channel blocker TEA+ at a high concentration (20 mm). Barium, another classical K+ channel blocker, inhibited K+ currents with a K
i
of about 1.3 mm. In contrast to guard cells, the cytosolic Ca2+ level proved to be ineffective in regulating the K+ conductance at hyperpolarization. External Ca2+ blocked currents weakly in a voltage-dependent manner. From instantaneous current-voltage curves, we identified a binding site in the channel pore with an electrical distance of about 0.2 to 0.5. Lanthanum ions reduced the inward current in a voltage-dependent manner and simultaneously displaced the voltage at which half of the channels are in the open state to more positive values. This finding was interpreted as resulting from a sum of two molecular effects, an interaction with the mouth of the channel that causes a reduction of current, and a binding to the voltage sensor, leading to a shielding of surface charges and, subsequently, a modulation of channel gating.A comparison between the K+ inward rectifier in xylem parenchyma cells, guard cells and KAT1 from Arabidopsis leads to the conclusion that these rectifiers form subtypes within one class of ion channels. The ineffectiveness of Ca2+ to control K+ influx in xylem parenchyma cells is interpreted in physiological terms. 相似文献
9.
Summary We examined the variability of occurrence and frequency of voltage-dependent whole-cell currents in human peripheral blood monocyte-derived macrophages (HMDM) maintained in culture for up to three weeks. An increase in cell capacitance from an average value of 9 pF on the day of isolation to 117 pF at 14 days accompanied growth and differentiation in culture. The average resting potential was approximately –34 mV for cells beyond two days in culture. Cells exhibited a voltage-and time-dependent outward current upon membrane depolarization above approximately –30 mV, which appeared to be composed of a number of separate currents with variable expression from donor to donor. Three of these currents are carried by K+. The frequency of each outward current type was calculated for 974 cells obtained from 36 donors. The HMDMs in these studies exhibited two 4-aminopyridine (4-AP) sensitive, time-dependent outward currents (I
A
andI
B
) that could be differentiated on the basis of the presence or absence of steady-state inactivation in the physiological potential range, time course of inactivation during maintained depolarization, as well as threshold of activation. The 4-AP-insensitive outward current activated at approximately 10 mV. One component of the 4-AP insensitive-outward current (I
C
) could be blocked by external TEA and by the exchange of internal Cs+ or Na+ for K+. The probability of observingI
B
andI
C
appeared to be donor dependent. Following total replacement of internal K+ with Cs+, two additional currents could be identified (i) a delayed component of outward current (I
D
) remained which could be blocked by low concentrations of external Zn2+ (4 m) and was insensitive to anion replacement in the external solution and (ii) a Cl– current with a reversal potential which shifted in the presence of external anion replacement and which was irreversibly inhibited by the stilbene SITS. The activation of a prominent time-independent inward currents was often observed with increasing hyperpolarization. This inward current was blocked by external Ba2+ and corresponded to the inwardly rectifying K+ current. Neither inward nor outward current expression appeared dependent on whether cells were differentiated in adherent or suspension culture nor was there demonstrable differential current expression observed upon transition from suspension to adherent form. 相似文献
10.
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
11.
The initial response of coleoptile cells to growth hormones and light is a rapid change in plasma-membrane polarization. We have isolated protoplasts from the cortex of maize (Zea mays L.) coleoptiles to study the electrical properties of their plasma membrane by the patch-clamp techniqueUsing the whole-cell configuration and cell-free membrane patches we could identify an H+-ATPase, hyperpolarizing the membrane potential often more negative than -150 mV, and a voltage-dependent, inward-rectifying K+ channel (unit conductance 5–7 pS) as the major membrane conductan-ces Potassium currents through this channel named CKC1in (for Coleoptile K
+ Channel inward rectifier) were elicited upon voltage steps negative to -80 mV, characterized by a half-activation potential of -112 mV. The kinetics of activation, well described by a double-exponential process, were strongly dependent on the degree of hyperpolarization and the cytoplasmic Ca2+ level. Whereas at nanomolar Ca2+ concentrations K+ currents increased with a t1/2=16 ms (at -180 mV), higher calcium levels slowed the activation process about fourto fivefoldUpon changes in the extracellular K+ concentration the reversal potential of the K+ channel followed the Nernst potential for potassium with a 56-mV shift for a tenfold increaseThe absence of a measurable conductance for Na+, Rb+, Cs+ and a permeability ratio PNH
4
+
/PK+ around 0.25 underlines the high selectivity of CKC1in for K+In contrast to Cs+, which at submillimolar concentration blocks the channel in a voltage-dependent manner, Rb+, often used as a tracer for K+, does not permeate this type of K+ channelThe lack of Rb+ permeability is unique with respect to other K+ transporters. Therefore, future molecular analysis of CKC1in, considered as a unique variation of plant inward rectifiers, might help to understand the permeation properties of K+ channels in general.Abbreviations CKC1in
Coleoptile K
+ Channel inward rectifier
- U
membrane voltage
- Iss
steady-state currents
- Itail
tail currents
Experiments were conducted in the laboratory of F.G. during the stay of RHas a guest professor sponsored by Special Project RAISA, subproject N2.1, paper N2155. 相似文献
12.
Summary The whole-cell patch-clamp method has been used to measure Ca2+ influx through otherwise K+-selective channels in the plasma membrane surrounding protoplasts from guard cells of Vicia faba. These channels are activated by membrane hyperpolarization. The resulting K+ influx contributes to the increase in guard cell turgor which causes stomatal opening during the regulation of leaf-air gas exchange. We find that after opening the K+ channels by hyperpolarization, depolarization of the membrane results in tail current at voltages where there is no electrochemical force to drive K+ inward through the channels. Tail current remains when the reversal potential for permeant ions other than Ca2+ is more negative than or equal to the K+ equilibrium potential (–47 mV), indicating that the current is due to Ca2+ influx through the K+ channels prior to their closure. Decreasing internal [Ca2+] (Ca
i
) from 200 to 2 nm or increasing the external [Ca2+] (Ca
o
) from 1 to 10 mm increases the amplitude of tail current and shifts the observed reversal potential to more positive values. Such increases in the electrochemical force driving Ca2+ influx also decrease the amplitude of time-activated current, indicating that Ca2+ permeation is slower than K+ permeation, and so causes a partial block. Increasing Ca
o
also (i) causes a positive shift in the voltage dependence of current, presumably by decreasing the membrane surface potential, and (ii) results in a U-shaped current-voltage relationship with peak inward current ca. –160 mV, indicating that the Ca2– block is voltage dependent and suggesting that the cation binding site is within the electric field of the membrane. K+ channels in Zea mays guard cells also appear to have a Ca
i
-, and Ca
o
-dependent ability to mediate Ca2+ influx. We suggest that the inwardly rectiying K+ channels are part of a regulatory mechanism for Ca
i
. Changes in Ca
o
and (associated) changes in Ca
i
regulate a variety of intracellular processes and ion fluxes, including the K+ and anion fluxes associated with stomatal aperture change.This work was supported by grants to S.M.A. from NSF (DCB-8904041) and from the McKnight Foundation. K.F.-G. is a Charles Gilbert Heydon Travelling Fellow. The authors thank Dr. R. MacKinnon (Harvard Medical School) and two anonymous reviewers for helpful comments. 相似文献
13.
Summary Human red cells were prepared with various cellular Na+ and K+ concentrations at a constant sum of 156mm. At maximal activation of the K+ conductance,g
K(Ca), the net efflux of K+ was determined as a function of the cellular Na+ and K+ concentrations and the membrane potential,V
m
, at a fixed [K+]ex of 3.5mm.V
m
was only varied from (V
m
–E
K)25 mV and upwards, that is, outside the range of potentials with a steep inward rectifying voltage dependence (Stampe & Vestergaard-Bogind, 1988).g
K(Ca) as a function of cellular Na+ and K+ concentrations atV
m
=–40, 0 and 40 mV indicated a competitive, voltage-dependent block of the outward current conductance by cellular Na+. Since the present Ca2+-activated K+ channels have been shown to be of the multi-ion type, the experimental data from each set of Na+ and K+ concentrations were fitted separately to a Boltzmann-type equation, assuming that the outward current conductance in the absence of cellular Na+ is independent of voltage. The equivalent valence determined in this way was a function of the cellular Na+ concentration increasing from 0.5 to 1.5 as this concentration increased from 11 to 101mm. Data from a previous study of voltage dependence as a function of the degree of Ca2+ activation of the channel could be accounted for in this way as well. It is therefore suggested that the voltage dependence ofg
K(Ca) for outward currents at (V
m
–E
K)>25 25 mV reflects a voltage-dependent Na+ block of the Ca2+-activated K+ channels. 相似文献
14.
Margaret Colden-Stanfield William P. Schilling Lourival D. Possani Diana L. Kunze 《The Journal of membrane biology》1990,116(3):227-238
Summary Bovine aortic endothelial cells (BAECs) respond to bradykinin with an increase in cytosolic-free Ca2+ concentration, [Ca2+]
i
, accompanied by an increase in surface membrane K+ permeability. In this study, electrophysiological measurement of K+ current was combined with86Rb+ efflux measurements to characterize the K+ flux pathway in BAECs. Bradykinin- and Ca2+-activated K+ currents were identified and shown to be blocked by the alkylammonium compound, tetrabutylammonium chloride and by the scorpion toxin,noxiustoxin, but not by apamin or tetraethylammonium chloride. Whole-cell and single-channel current analysis suggest that the threshold for Ca2+ activation is in the range of 10 to 100nm [Ca2+]
i
. The whole-cell current measurement show voltage sensitivity only at the membrane potentials more positive than 0 mV where significant current decay occurs during a sustained depolarizing pulse. Another K+ current present in control conditions, an inwardly rectifying K+ current, was blocked by Ba2+ and was not affected bynoxiustoxin or tetrabutylammonium chloride. Efflux of86Rb– from BAEC monolayers was stimulated by both bradykinin and ionomycin. Stimulated efflux was blocked by tetrabutyl- and tetrapentyl-ammonium chloride and bynoxiustoxin, but not by apamin or furosemide. Thus,86Rb+ efflux stimulated by bradykinin and ionomycin has the same pharmacological sensitivity as the bradykinin- and Ca2+-activated membrane currents. The results confirm that bradykinin-stimulated86Rb+ efflux occurs via Ca2+-activated K+ channels. The blocking agents identified may provide a means for interpreting the role of the Ca2+-activated K+ current in the response of BAECs to bradykinin. 相似文献
15.
Inward currents in root cap protoplasts of the aluminum-tolerant cultivar, Dade, of Phaseolus vulgaris L. were investigated using the whole-cell patch-clamp technique. The properties of these currents were similar to those seen in inward rectifying K+ channels in other plant tissues. Replacing bath K+ with Na+ nearly abolished the observed currents. Higher bath K+ concentrations increased inward currents. AlCl3 in pH 4.7 bath solutions caused inward K+ currents to activate more rapidly and at more positive voltages when compared with AlCl3 free solutions. In 10 μM AlCl3 the activated inward K+ currents were significantly larger than in the AlCl3-free solution at all voltages except at the most negative voltage of −174 mV and the least negative of −74 mV. In contrast, in 80 μM Al3+, when hyperpolarizing voltages were most negative, the inward K+ currents were inhibited relative to the currents in 10 μM AlCl3. Enhancement of inward K+ currents by AlCl3 is consistent with Al3+ binding to the external surface of the root cap protoplast, decreasing the surface charge, thus causing the channels to sense a more negative membrane potential. Inhibition of inward K+ currents with higher AlCl3 concentrations and more negative voltages is consistent with Al3+ block of K+ channels.This revised version was published online in August 2005 with a corrected cover date. 相似文献
16.
Using the two-microelectrode voltage clamp technique in Xenopus laevis oocytes, we estimated Na+-K+-ATPase activity from the dihydroouabain-sensitive current (I
DHO) in the presence of increasing concentrations of tetraethylammonium (TEA+; 0, 5, 10, 20, 40 mm), a well-known blocker of K+ channels. The effects of TEA+ on the total oocyte currents could be separated into two distinct parts: generation of a nonsaturating inward current increasing with negative membrane potentials (V
M) and a saturable inhibitory component affecting an outward current easily detectable at positive V
M. The nonsaturating component appears to be a barium-sensitive electrodiffusion of TEA+ which can be described by the Goldman-Hodgkin-Katz equation, while the saturating component is consistent with the expected blocking effect of TEA+ on K+ channels. Interestingly, this latter component disappears when the Na+-K+-ATPase is inhibited by 10 m DHO. Conversely, TEA+ inhibits a component of I
DHO with a k
d of 25±4 mm at +50 mV. As the TEA+-sensitive current present in I
DHO reversed at –75 mV, we hypothesized that it could come from an inhibition of K+ channels whose activity varies in parallel with the Na+-K+-ATPase activity. Supporting this hypothesis, the inward portion of this TEA+-sensitive current can be completely abolished by the addition of 1 mm Ba2+ to the bath. This study suggests that, in X. laevis oocytes, a close link exists between the Na-K-ATPase activity and TEA+-sensitive K+ currents and indicates that, in the absence of effective K+ channel inhibitors, I
DHO does not exclusively represent the Na+-K+-ATPase-generated current. 相似文献
17.
Summary The effects of tetraethylammonium ions on currents through high-conductance voltage- and Ca2+-activated K+ channels have been studied with the help of patch-clamp single-channel and whole-cell current recording on pig pancreatic acinar cells. In excised outside-out membrane patches TEA (1 to 2 mM) added to the bath solution virtually abolishes unitary current activity except at very positive membrane potentials when unitary currents corresponding to a markedly reduced conductance are observed. TEA in a lower concentration (0.2 mM) markedly reduces the open-state probability and causes some reduction of the single-channel conductance. In inside-out membrane patches bath application of TEA in concentrations up to 2 mM has no effect on single-channel currents. At a higher concentration (10 mM) slight reductions in single-channel conductance occur. In whole-cell current recording experiments TEA (1 to 2 mM) added to the bath solution completely suppresses the outward currents associated with depolarizing voltage jumps to membrane potentials of 0 mV and blocks the major part (70 to 90%) of the outward currents even at very positive membrane potentials (30 to 40 mV). In contrast TEA (2 mM) added to the cell interior (pipette solution) has no effect on the outward K+ current. Our results demonstrate that TEA in low concentrations (1 to 2 mM) acts specifically on the outside of the plasma membrane to block current through the high-conductance Ca2+- and voltage-activated K+ channels 相似文献
18.
The role of the inward K+ rectifier in the repetitive activity at depolarized levels was studied in guinea pig single ventricular myocytes by voltage- and current-clamp methods. In action potentials arrested at the plateau by a depolarizing current, small superimposed hyperpolarizing currents caused much larger voltage displacements than at the resting potential and sometimes induced a regenerative repolarization. Around –20 mV, sub- and suprathreshold repetitive inward currents were found. In the same voltage range, small hyperpolarizing currents reversed their polarity. During depolarizing voltage-clamp ramps, around –20 mV there was a sudden decrease in the outward current (Ins: current underlying the negative slope in the inward K+ rectifier steady state I–V relation). During repolarizing ramps, the reincrease in outward current was smaller and slower. During depolarizing and repolarizing current ramps, sudden voltage displacements showed a similar asymmetry. Repetitive Ins could continue as long as the potential was kept at the level at which they appeared. Depolarizing voltage-clamp steps also caused repetitive Ins and depolarizing current steps induced repetitive slow responses. Cadmium and verapamil reduced Ins amplitude during the depolarizing ramp. BRL 34915 (cromakalim), an opener of the ATP-sensitive K+ channel, eliminated the negative slope and Ins, whereas barium increased Ins frequency (an effect abolished by adding BRL). Depolarization-induced slow responses persisted in an NaCl-Ca-free solution. Thus, the mechanism of repetitive activity at the depolarized level appears to be related to the presence of the negative slope in the inward K+ rectifier I–V relation. 相似文献
19.
Using the voltage-clamp technique, we investigated transmembrane ion currents in isolated smooth muscle cells of the guinea
pigtaenia coli. In our study, we identified and studied a charibdotoxin-sensitive component of Ca2+-dependent K+ current carried through the channels of high conductance (in most publications called “big conductance,”I
BK(Ca)). This component was completely blocked by 100 nM charibdotoxin and by tetraethylammonium in concentrations as low as 1 mM.I
BK(Ca) demonstrated fast kinetics of inactivation, which nearly coincided with that of Ca2+ current. In addition to the dependence on Ca2+ concentration, this current also showed voltage-dependent properties: with a rise in the level of depolarization its amplitude
increased. In many cells, depolarizing shifts in the membrane potential evoke spontaneous outward currents. Such currents
probably represent the secondary effect of cyclic Ca2+ release from the caffeine-sensitive intracellular stores that result in short-term activation of charibdotoxin-sensitive
Ca2+-dependent K+ channels. 相似文献
20.
Palle Christophersen 《The Journal of membrane biology》1991,119(1):75-83
Summary The Ca2+-activated K+ channel of the human red cell membranes was characterized with respect to rectification and selectivity using the patch-clamp technique. In inside-out patches exposed to symmetric solutions of K+, Rb+, and NH
4
+
, respectively, inward rectifyingi-V curves were obtained. The zero current conductances were: K+ (23.5 pS±3.2)>NH
4
+
(14.2 pS±1.2)>Rb+ (11.4 pS±1.8). With low extracellular K+ concentrations (substitution with Na+) the current fluctuations reversed close to the Nernst potential for the K ion and the rectification as well as thei-V slopes decreased. With mixed intracellular solutions of K+ and Na+ enhanced rectification were observed due to a Na+ block of outward currents. From bi-ionic reversal potentials the following permeability sequence (P
K/P
X) was calculated: K+ (1.0)>Rb+ (1.4±0.1)>NH
4
+
(8.5±1.3)>Li+(>50); Na+ (>110); Cs+ (5). Li+, Na+, and Cs+ were not found to carry any current, and only minimum values of the permeability ratios were estimated. Tl+ was permeant, but the permeability and conductance were difficult to quantify, since with this ion the single channel activity was extremely low and the channels seemed to inactivate. The inward rectification in symmetric solutions indicate an asymmetric open channel structure, and the different selectivity sequences based on conductances and permeabilities reflect interionic interactions in the permeation process. 相似文献