共查询到20条相似文献,搜索用时 15 毫秒
1.
N.A. Sunstrom L.S. Premkumar A. Premkumar G. Ewart G.B. Cox P.W. Gage 《The Journal of membrane biology》1996,150(2):127-132
The influenza B virus protein, NB, was expressed in Escherichia coli, either with a C-terminal polyhistidine tag or with NB fused to the C-terminus of glutathione S-transferase (GST), and purified
by affinity chromatography. NB produced ion channel activity when added to artificial lipid bilayers separating NaCl solutions
with unequal concentrations (150–500 mm
cis, 50 mm
trans). An antibody to a peptide mimicking the 25 residues at the C-terminal end of NB, and amantadine at high concentration (2–3
mm), both depressed ion channel activity. Ion channels had a variable conductance, the lowest conductance observed being approximately
10 picosiemens. At a pH of 5.5 to 6.5, currents reversed at positive potentials indicating that the channel was more permeable
to sodium than to chloride ions (PNa/PCl∼ 9). In asymmetrical NaCl solutions at a pH of 2.5, currents reversed closer to the chloride than to the sodium equilibrium
potential indicating that the channel had become more permeable to chloride than to sodium ions (PCl/PNa∼ 4). It was concluded that, at normal pHs, NB forms cation-selective channels.
Received: 6 March 1995/Revised: 17 November 1995 相似文献
2.
A.M. Feigin J.Y. Takemoto R. Wangspa J.H. Teeter J.G. Brand 《The Journal of membrane biology》1996,149(1):41-47
Using the planar lipid bilayer technique we demonstrate that the lipodepsipeptide antibiotic, syringomycin E, forms voltage-sensitive
ion channels of weak anion selectivity. The formation of channels in bilayers made from dioleoylglycerophosphatidylserine
doped with syringomycin E at one side (1–40 μg/ml) was greatly affected by cis-positive voltage. A change of voltage from a positive to a negative value resulted in (i) an abrupt increase in the single
channel conductance (the rate of increase was voltage dependent) simultaneous with (ii) a closing of these channels and an
exponential decrease in macroscopic conductance over time. The strong voltage dependence of multichannel steady state conductance,
the single channel conductance, the rate of opening of channels at positive voltages and closing them at negative voltages,
as well as the observed abrupt increase of single channel conductance after voltage sign reversal suggest that the change
of the transmembrane field induces a significant rearrangement of syringomycin E channels, including a change in the spacing
of charged groups that function as voltage sensors. The conductance induced by syringomycin E increased with the sixth power
of syringomycin E concentration suggesting that at least six monomers are required for channel formation.
Received: 3 April 1995/Revised: 24 August 1995 相似文献
3.
Lanthanide ions such as La3+ are frequently used as blockers to test the involvement of calcium channels in plant and animal signal transduction pathways.
For example, the large rise in cytoplasmic Ca2+ concentration triggered by cold shock in Arabidopsis seedlings is effectively blocked by 10 mm La3+ and we show here that the simultaneous large membrane depolarization is similarly blocked. However, a pharmacological tool
is only as useful as it is selective and the specificity of La3+ for calcium channels was brought into question by our finding that it also blocked a blue light (BL)-induced depolarization
that results from anion channel activation and believed not to involve calcium channels. This unexpected inhibitory effect
of La3+ on the BL-induced depolarization is explained by our finding that 10 mm La3+ directly and completely blocked the BL-activated anion channel when applied to excised patches. We have investigated the
ability of La3+ to block noncalcium channels in Arabidopsis. In addition to the BL-activated anion channel, 10 mm La3+ blocked a cation channel and a stretch-activated channel in patches of plasma membrane excised from hypocotyl cells. In root
cells, 10 mm La3+ inhibited the activity of an outward-rectifying potassium channel at the whole cell and single-channel level by 47% and 58%,
respectively. We conclude that La3+ is a nonspecific blocker of multiple ionic conductances in Arabidopsis and may disrupt signal transduction processes independently of any effect on Ca2+ channels.
Received: 28 July 1997/Revised: 13 November 1997 相似文献
4.
Qu W Zhu XO Moorhouse AJ Bieri S Cunningham AM Barry PH 《The Journal of membrane biology》2000,178(2):137-150
The permeation properties of adenosine 3′, 5′-cyclic monophosphate (cAMP)-activated recombinant rat olfactory cyclic nucleotide-gated
channels (rOCNC1) in human embryonic kidney (HEK 293) cells were investigated using inside-out excised membrane patches. The
relative permeability of these rOCNC1 channels to monovalent alkali cations and organic cations was determined from measurements
of the changes in reversal potential upon replacing sodium in the bathing solution with different test cations. The permeability
ratio of Cl− relative to Na+ (P
Cl
/P
Na
) was about 0.14, confirming that these channels are mainly permeable to cations. The sequence of relative permeabilities
of monovalent alkali metal ions in these channels was P
Na
≥P
K
> P
Li
> P
Cs
≥P
Rb
, which closely corresponds to a high-strength field sequence as previously determined for native rat olfactory receptor neurons
(ORNs). The permeability sequence for organic cations relative to sodium was P
NH3OH
> P
NH4
> P
Na
> P
Tris
> P
Choline
> P
TEA
, again in good agreement with previous permeability ratios obtained in native rat ORNs. Single-channel conductance sequences
agreed surprisingly well with permeability sequences. These conductance measurements also indicated that, even in asymmetric
bi-ionic cation solutions, the conductance was somewhat independent of current direction and dependent on the composition
of both solutions. These results indicate that the permeability properties of rOCNC1 channels are similar to those of native
rat CNG channels, and provide a suitable reference point for exploring the molecular basis of ion selectivity in recombinant
rOCNC1 channels using site-directed mutagenesis.
Received: 3 July 2000/Revised: 29 August 2000 相似文献
5.
The role of glycosylation on voltage-dependent channel gating for the cloned human cardiac sodium channel (hH1a) and the
adult rat skeletal muscle isoform (μl) was investigated in HEK293 cells transiently transfected with either hH1a or μl cDNA.
The contribution of sugar residues to channel gating was examined in transfected cells pretreated with various glycosidase
and enzyme inhibitors to deglycosylate channel proteins. Pretreating transfected cells with enzyme inhibitors castanospermine
and swainsonine, or exo-glycosidase neuroaminidase caused 7 to 9 mV depolarizing shifts of V
1/2 for steady-state activation of hH1a, while deglycosylation with corresponding drugs elicited about the same amount of depolarizing
shifts (8 to 9 mV) of V
1/2 for steady-state activation of μl. Elevated concentrations of extracellular Mg2+ significantly masked the castanospermine-elicited depolarizing shifts of V
1/2 for steady-state activation in both transfected hH1a and μl. For steady-state activation, deglycosylation induced depolarizing
shifts of V
1/2 for hH1a (10.6 to 12 mV), but hyperpolarizing shifts for μl (3.6 to 4.4 mV). Pretreatment with neuraminidase had no significant
effects on single-channel conductance, the mean open time, and the open probability. These data suggest that glycosylation
differentially regulates Na channel function in heart and skeletal muscle myocytes.
Received: 8 April 1999/Revised: 18 June 1999 相似文献
6.
The permeation properties of KAT1, an inward rectifying potassium channel from plant cells, were investigated with different
ions in the external medium. With either K+, NH+
4 or methylammonium (MA) in the external solution, the channel, expressed in Xenopus oocytes, appeared permeable to K+ and, to a lesser extent, to NH+
4 but not to the slightly bigger, methylated analogue of NH+
4, MA. Substituting NH+
4 for K+ shifted the voltage dependency of channel activation further negative and hastened activation kinetics. This suggests that
channel operation depends on the transported substrate. In mixed solution (50 mm K+, 50 mm MA) MA inhibited K+ current in a voltage-independent manner. The maximum block did not exceed 50% of the K+ current. In contrast, when NH+
4 was the permeant ion (50 mm NH+
4, 50 mm MA) MA caused a voltage-dependent, slowly developing open channel block, achieving complete inhibition at very negative voltages.
The latter block could be partially overcome by the addition of K+ in the external solution. The data support a model in which ions, after entering the channel pore, compete with different
affinities for binding sites on their permeation pathway.
Received: 6 October 1997/Revised: 28 January 1998 相似文献
7.
8.
The THP-1 human monocytic leukemia cell line is a useful model of macrophage differentiation. Patch clamp methods were used
to identify five types of ion channels in undifferentiated THP-1 monocytes. (i) Delayed rectifier K+ current, I
DR, was activated by depolarization to potentials positive to −50 mV, inactivated with a time constant of several hundred msec,
and recovered from inactivation with a time constant ∼21 sec. I
DR was inhibited by 4-aminopyridine (4-AP), tetraethylammonium (TEA+), and potently by charybdotoxin (ChTX). (ii) Ca-activated K+ current (I
SK) dominated whole-cell currents in cells studied with 3–10 μm [Ca2+]
i
. I
SK was at most weakly voltage-dependent, with reduced conductance at large positive potentials, and was inhibited by ChTX and
weakly by TEA+, Cs+, and Ba2+, but not 4-AP or apamin. Block by Cs+ and Ba2+ was enhanced by hyperpolarization. (iii) Nonselective cation current, I
cat, appeared at voltages above +20 mV. Little time-dependence was observed, and a panel of channel blockers was without effect.
(iv) Chloride current, I
Cl, was present early in experiments, but disappeared with time. (v) Voltage-activated H+ selective current is described in detail in a companion paper (DeCoursey & Cherny, 1996. J. Membrane Biol.
152:2). The ion channels in THP-1 cells are compared with channels described in other macrophage-related cells. Profound changes
in ion channel expression that occur during differentiation of THP-1 cells are described in a companion paper (DeCoursey et
al., 1996. J. Membrane Biol.
152:2).
Received: 19 September 1995/Revised: 14 March 1996 相似文献
9.
J.-P. Bénitah J.R. Balser E. Marban G.F. Tomaselli 《The Journal of membrane biology》1997,155(2):121-131
Extracellular acidosis affects both permeation and gating of the expressed rat skeletal muscle Na+ channel (μ1). Reduction of the extracellular pH produced a progressive decrease in the maximal whole-cell conductance and
a depolarizing shift in the whole-cell current-voltage relationship. A smaller depolarizing shift in the steady-state inactivation
curve was observed. The pK of the reduction of maximal conductance was 6.1 over the pH range studied. An upper limit estimate
of the pK of the shift of the half-activation voltage was 6.1. The relative reduction in the maximal whole-cell conductance
did not change with higher [Na+]
o
. The conductance of single fenvalerate-modified Na+ channels was reduced by extracellular protons. Although the single-channel conductance increased with higher [Na+]
o
, the maximal conductances at pH 7.6, 7.0 and 6.0 did not converge at [Na+]
o
up to 280 mm, inconsistent with a simple electrostatic effect. A model incorporating both Na+ and H+ binding in the pore and cation binding to a Gouy-Chapman surface charge provided a robust fit to the single-channel conductance
data with an estimated surface charge density of 1e−/439?2. Neither surface charge nor proton block alone suffices to explain the effects of extracellular acidosis on Na+ channel permeation; both effects play major roles in mediating the response to extracellular pH.
Received: 14 May 1996/Revised: 19 September 1996 相似文献
10.
A Patch-Clamp Study of Ion Channels in Protoplasts Prepared from the Marine Alga Valonia utricularis
The giant marine alga Valonia utricularis is a classical model system for studying the electrophysiology and water relations of plant cells by using microelectrode
and pressure probe techniques. The recent finding that protoplasts can be prepared from the giant ``mother cells' (Wang,
J., Sukhorukov, V.L., Djuzenova, C.S., Zimmermann, U., Müller, T., Fuhr, G., 1997, Protoplasma
196:123–134) allowed the use of the patch-clamp technique to examine ion channel activity in the plasmalemma of this species.
Outside-out and cell-attached experiments displayed three different types of voltage-gated Cl− channels (VAC1, VAC2, VAC3, Valonia Anion Channel 1,2,3), one voltage-gated K+ channel (VKC1, Valonia K
+
Channel 1) as well as stretch-activated channels. In symmetrical 150 mm Cl− media, VAC1 was most frequently observed and had a single channel conductance of 36 ± 7 pS (n= 4) in the outside-out and 33 ± 5 pS (n= 10) in the cell-attached configuration. The reversal potential of the corresponding current-voltage curves was within 0
± 4 mV (n= 4, outside-out) and 9 ± 7 mV (n= 10, cell-attached) close to the Nernst potential of Cl− and shifted towards more negative values when cell-attached experiments were performed in asymmetrical 50:150 mm Cl− media (bath/pipette; E
Cl−
−20 ± 7 mV (n= 4); Nernst potential −28 mV). Consistent with a selectivity for Cl−, VAC1 was inhibited by 100 μM DIDS (4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid). VAC1 was activated by a hyperpolarization of the patch. Boltzmann
fits of the channel activity under symmetrical 150 mm Cl− conditions yielded a midpoint potential of −12 ± 5 mV (n= 4, outside-out) and −3 ± 6 mV (n= 9, cell-attached) and corresponding apparent minimum gating charges of 15 ± 3 (n= 4) and 18 ± 5 (n= 9). The midpoint potential shifted to more negative values in the presence of a Cl− gradient.
VAC2 was activated by voltages more negative than E
Cl−
and was always observed together with VAC1, but less frequently. It showed a ``flickering' gating. The single channel conductance
was 99 ± 10 pS (n= 6). VAC3 was activated by membrane depolarization and frequently exhibited several subconductance states. The single channel
conductance of the main conductance state was 36 ± 5 pS (n= 5). VKC1 was also activated by positive clamped voltages. Up to three conductance states occurred whereby the main conductance
state had a single channel conductance of 124 ± 27 pS (n= 6).
In the light of the above results it seems to be likely that VAC1 contributes mainly to the Cl− conductance of the plasmalemma of the turgescent ``mother cells' and that this channel (as well as VAC2) can operate in
the physiological membrane potential range. The physiological significance of VAC3 and VKC1 is unknown, but may be related
(as the stretch-activated channels) to processes involved in turgor regulation.
Received: 24 June 1999/Revised: 2 September 1999 相似文献
11.
Ionic channels of the sugar beet tonoplast were studied using the patch-clamp technique. At micromolar concentrations of
cytosolic calcium, several (at least four) distinct single-channel current levels were routinely identified. On the basis
of channel voltage dependence, kinetic properties and conductance of single openings, the largest channel (103 ± 2 pS in symmetric
150 mm KCl) corresponds to the slow vacuolar (SV) channel already identified by Hedrich and Neher (1987). The majority of the whole-vacuole
current was ascribed to this time-dependent slow-activating channel elicited by positive vacuolar potentials. The channel
of intermediate amplitude (41 ± 1 pS in 150 mm KCl) did not show any voltage dependence and delay in the activation upon the application of voltage steps to both positive
and negative transmembrane potentials. Owing to its voltage independence this channel was denominated FV1. The opening probability
of the SV-type channel increased by increasing the cytoplasmic calcium concentration, while the activity of the FV1 channel
did not increase appreciably by changing the calcium concentration in the range from 6 μm to 1 mm. All the channels identified showed a linear current-voltage characteristic in the range ±100 mV and at least the three most
conductive ones displayed potassium selectivity properties. Substitution of potassium with tetramethylammonium (TMA) on the
cytosolic side demonstrated that both the SV and FV1 channels are impermeable to TMA influx into the vacuole and support the
potassium selectivity properties of these two channels. Moreover, the single channel conductances of all the channels identified
increased as a function of the potassium concentration and reached a maximum conductivity at [K+] ∼0.5 m. This behavior can be explained by a multi-ion occupancy single-file permeation mechanism.
Received: 26 December 1995/Revised: 10 July 1996 相似文献
12.
We present three mechanisms by which Na+ inhibits the open channel currents of the predominant K+ channel in the tonoplast of Chara corallina: (i) Fast block, i.e., short (100 ns range) interruptions of the open channel current which are determined by open channel noise analysis, (ii): Oligo-subconductance
mode, i.e., a gating mode which occurs preferentially in the presence of Na+; this mode comprises a discrete number (here 3) of open states with smaller conductances than normal, and (iii): Polysubconductance
mode, i.e., a gating mode with a nondiscrete, large number (>30) of states with smaller conductances than the main open channel
conductance. This novel mode has also been observed only in the presence of Na+.
Received: 16 November 1999/Revised: 8 February 2000 相似文献
13.
P2X2 purinoceptors are cation-selective channels activated by ATP and its analogues. Using single channel measurements we studied
the channel's selectivity for the alkali metal ions and organic monovalent cations NMDG+, Tris+, TMA+, and TEA+. The selectivity sequence for currents carried by alkali metal ions is: K+ > Rb+ > Cs+ > Na+ > Li+, which is Eisenman sequence IV. This is different from the mobility sequence of the ions in free solution suggesting there is weak interaction
between the ions and the channel interior. The relative conductance for alkali ions increases linearly in relation to the
Stokes radius. The organic ions NMDG+, Tris+, TMA+ and TEA+ were virtually impermeant. The divalent ions (Mn2+, Mg2+, Ca2+ and Ba2+) induced a fast block visible as a reduction in amplitude of the unitary currents. Using a single-site binding model, the
divalent ions exhibited an equilibrium affinity sequence of Mn2+ > Mg2+ > Ca2+ > Ba2+.
Received: 3 May 1999/Revised: 23 August 1999 相似文献
14.
Certain COOH-terminus mutants of connexin32 (Cx32) were previously shown to form channels with unusual transjuctional voltage
(V
j
) sensitivity when tested heterotypically in oocytes against Cx32 wild type. Junctional conductance (G
j
) slowly increased by severalfold or decreases to nearly zero with V
j
positive or negative, respectively, at mutant side, and V
j
positive at mutant side reversed CO2-induced uncoupling. This suggested that the CO2-sensitive gate might be a V
j
-sensitive slow gate. Based on previous data for calmodulin (CaM) involvement in gap junction function, we have hypothesized
that the slow gate could be a CaM-like pore plugging molecule (cork gating model). This study describes a similar behavior
in heterotypic channels between Cx32 and each of four new Cx32 mutants modified in cytoplasmic-loop and/or COOH-terminus residues.
The mutants are: ML/NN+3R/N, 3R/N, ML/NN and ML/EE; in these mutants, N or E replace M105 and L106, and N replace R215, R219
and R220. This study also reports that inhibition of CaM expression strongly reduces V
j
and CO2 sensitivities of two of the most effective mutants, suggesting a CaM role in slow and chemical gating.
Received: 19 April 2000/Revised: 11 August 2000 相似文献
15.
C. Berrier M. Besnard B. Ajouz A. Coulombe A. Ghazi 《The Journal of membrane biology》1996,151(2):175-187
Mechanosensitive ion channels from Escherichia coli were studied in giant proteoliposomes reconstituted from an inner membrane fraction, or in giant round cells in which the
outer membrane and the cell wall had been disrupted by a lysozyme-EDTA treatment and a mild osmotic shock. Patch-clamp experiments
revealed the presence in these two preparations of an array of different conductances (100 to 2,300 pS in 0.1 m KCl) activated by stretch. The electrical activity induced by stretch in the native membrane was complex, due to the activation
of several different conductances. In contrast, patches of proteoliposomes generally contained clusters of identical conductances,
which differed from patch to patch. These experiments are consistent with the notion that these different conductances correspond
to different proteins in the plasma membrane of E. coli, which segregate into clusters of identical channels on dilution involved in reconstitution in proteoliposomes. These conductances
could be grouped into three subfamilies of poorly selective channels. In both preparations, the higher the conductance, the
higher was the negative pressure needed for activation. We discuss the putative role of these channels as parts of a multicomponent
osmoregulatory system.
Received: 23 May 1995/Revised: 31 January 1996 相似文献
16.
Gap junction channels contain two hemichannels (connexons), each being a connexin (Cx) hexamer. In cells expressing multiple
connexins, heteromeric connexons are believed to form, whereas cell pairs expressing different connexins generate heterotypic
channels. To define gating behavior of heteromeric and heterotypic channels, CO2-induced gating was tested in Xenopus oocyte pairs expressing Cx32, or 5R/N (Cx32 mutant), as well as in pairs in which one oocyte (mx) expressed a 50/50 mixture
of Cx32 and 5R/N and the other either the mixture (mx), Cx32 (32) or 5R/N (R/N). In 5R/N, replacement of 5 C-terminus arginines
with asparagines greatly increased CO2 sensitivity. In response to 3 and 15 min CO2 exposures, junctional conductance (G
j
) decreased to 85% and 47%, in 32–32 pairs, and to 7% and 0.9%, in R/N-R/N pairs, respectively. In mx-mx and mix-32 pairs,
G
j
decreased to similar values (33% and 35%, respectively) with 15 min CO2. The sensitivity of mx-R/N pairs was similar to that of heterotypic 32-R/N pairs, as G
j
dropped to 36% and 38%, respectively, with 3 min CO2. Monoheteromeric (mx-32 and mx-R/N) and biheteromeric (mx-mx) channels behaved as if Cx32 were dominant, suggesting that
hemichannel sensitivity is not an average of the sensitivities of its connexin monomers. In contrast, heterotypic channels
behaved as if the two hemichannels of a cell-cell channel had no influence on each other.
Received: 15 May 1997/Revised: 8 December 1997 相似文献
17.
Cells from ten human meningiomas were electrophysiologically characterized in both living tissue slices and primary cultures.
In whole cells, depolarization to voltages higher than +80 mV evoked a large K+ outward current, which could be blocked by iberiotoxin (100 nm) and TEA (half blocking concentration IC50= 5.3 mm). Raising the internal Ca2+ from 10 nm to 2 mm shifted the voltage of half-maximum activation (V
1/2) of the K+ current from +106 to +4 mV. Respective inside-out patch recordings showed a voltage- and Ca2+-activated (BK
Ca
) K+ channel with a conductance of 296 pS (130 mm K+ at both sides of the patch). V
1/2 of single-channel currents was +6, −12, −46, and −68 mV in the presence of 1, 10, 100, and 1000 μm Ca2+, respectively, at the internal face of the patch. In cell-attached patches the open probability (P
o
) of BK
Ca
channels was nearly zero at potentials below +80 mV, matching the activation threshold for whole-cell K+ currents with 10 nm Ca2+ in the pipette. Application of 20 μm cytochalasin D increased P
o
of BK
Ca
channels in cell-attached patches within minutes. These data suggest that the activation of BK
Ca
channels in meningioma cells does not only depend on voltage and internal Ca2+ but is also controlled by the cytoskeleton.
Received 18 June 1999/Revised: 18 January 2000 相似文献
18.
Olfactory receptor neurons respond to odorants with G protein-mediated increases in the concentrations of cyclic adenosine 3',5'-monophosphate (cAMP) and/or inositol-1,4,5-trisphosphate (IP3). This study provides evidence that both second messengers can directly activate distinct ion channels in excised inside-out patches from the dendritic knob and soma membrane of rat olfactory receptor neurons (ORNs). The IP3-gated channels in the dendritic knob and soma membranes could be classified into two types, with conductances of 40 +/- 7 pS (n = 5) and 14 +/- 3 pS (n = 4), with the former having longer open dwell times. Estimated values of the densities of both channels from the same inside-out membrane patches were very much smaller for IP3-gated than for CNG channels. For example, in the dendritic knob membrane there were about 1000 CNG channels x microm(-2) compared to about 85 IP3-gated channels x microm(-2). Furthermore, only about 36% of the dendritic knob patches responded to IP3, whereas 83% of the same patches responded to cAMP. In the soma, both channel densities were lower, with the CNG channel density again being larger ( approximately 57 channels x microm(-2)) than that of the IP3-gated channels ( approximately 13 channels x microm(-2)), with again a much smaller fraction of patches responding to IP3 than to cAMP. These results were consistent with other evidence suggesting that the cAMP-pathway dominates the IP3 pathway in mammalian olfactory transduction. 相似文献
19.
Inhibition of Vacuolar Ion Channels by Polyamines 总被引:1,自引:0,他引:1
In this work, direct effects of cytosolic polyamines on the two principle vacuolar ion channels were studied by means of
patch-clamp technique. Fast and slow activating vacuolar channels were analyzed on membrane patches isolated from vacuoles
of the red beet taproot. The potency of the fast and of the slow vacuolar channel blockage by polyamines decreased with a
decrease of the polycation charge, spermine4+ > spermidine3+ > putrescine2+. In contrast to the inhibition of the fast vacuolar channel, the blockage of the slow vacuolar channel by polyamines displayed
a pronounced voltage-dependence. Hence, in the presence of high concentration of polyamines the slow vacuolar channel was
converted into a strong inward rectifier as evidenced by its unitary current-voltage characteristic. The blockage of the slow
vacuolar channel by polyamines was relieved at a large depolarization, in line with the permeation of polyamines through this
channel. The voltage-dependence of blockage was analyzed in terms of the conventional model, assuming a single binding site
for polyamines within the channel pore. Taking advantage of a simple linear structure of naturally occurring polyamines, conclusions
on a possible architecture of the slow vacuolar channel pore were drawn. The role of common polyamines in regulation of vacuolar
ion transport was discussed.
Received: 1 May 1998/Revised: 25 September 1998 相似文献
20.
The dependence of currents through the cyclic nucleotide-gated (CNG) channels of mammalian olfactory receptor neurons (ORNs)
on the concentration of NaCl was studied in excised inside-out patches from their dendritic knobs using the patch-clamp technique.
With a saturating concentration (100 μm) of adenosine 3′, 5′-cyclic monophosphate (cAMP), the changes in the reversal potential of macroscopic currents were studied
at NaCl concentrations from 25 to 300 mm. In symmetrical NaCl solutions without the addition of divalent cations, the current-voltage relations were almost linear,
reversing close to 0 mV. When the external NaCl concentration was maintained at 150 mm and the internal concentrations were varied, the reversal potentials of the cAMP-activated currents closely followed the
Na+ equilibrium potential indicating that P
Cl/P
Na≈ 0. However, at low external NaCl concentrations (≤100 mm) there was some significant chloride permeability. Our results further indicated that Na+ currents through these channels: (i) did not obey the independence principle; (ii) showed saturation kinetics with K
ms in the range of 100–150 mm and (iii) displayed a lack of voltage dependence of conductance in asymmetric solutions that suggested that ion-binding sites
were situated midway along the channel. Together, these characteristics indicate that the permeation properties of the olfactory
CNG channels are significantly different from those of photoreceptor CNG channels.
Received: 7 November 1996/Revised: 24 March 1997 相似文献