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1.
Nickel ions have been reported to exhibit differential effects on distinct subtypes of voltage-activated calcium channels.
To more precisely determine the effects of nickel, we have investigated the action of nickel on four classes of cloned neuronal
calcium channels (α1A, α1B, α1C, and α1E) transiently expressed in Xenopus oocytes. Nickel caused two major effects: (i) block detected as a reduction of the maximum slope conductance and (ii) a shift
in the current-voltage relation towards more depolarized potentials which was paralleled by a decrease in the slope of the
activation-curve. Block followed 1:1 kinetics and was most pronounced for α1C, followed by α1E > α1A > α1B channels. In contrast, the change in activation-gating was most dramatic with α1E, with the remaining channel subtypes significantly less affected. The current-voltage shift was well described by a simple
model in which nickel binding to a saturable site resulted in altered gating behavior. The affinity for both the blocking
site and the putative gating site were reduced with increasing concentration of external permeant ion. Replacement of barium
with calcium reduced both the degree of nickel block and the maximal effect on gating for α1A channels, but increased the nickel blocking affinity for α1E channels. The coexpression of Ca channel β subunits was found to differentially influence nickel effects on α1A, as coexpression with β2a or with β4 resulted in larger current-voltage shifts than those observed in the presence of β1b, while elimination of the β subunit almost completely abolished the gating shifts. In contrast, block was similar for the
three β subunits tested, while complete removal of the β subunit resulted in an increase in blocking affinity. Our data suggest
that the effect of nickel on calcium channels is complex, cannot be described by a single site of action, and differs qualitatively
and quantitatively among individual subtypes and subunit combinations.
Received: 12 October 1995/Revised: 17 January 1996 相似文献
2.
G.W. Zamponi 《The Journal of membrane biology》1999,167(2):183-192
Piperidines are a relatively novel class of calcium channel blockers which act at a unique receptor site associated with
the calcium channel α1 subunit. Calcium channel blocking affinities ranging from subnanomolar to several hundred micromolar have been reported in
the literature, suggesting that piperidine block is highly sensitive to the cellular environment experienced by the channel.
Here, I have investigated some of the cytoplasmic determinants of haloperidol block of N-type calcium channels expressed in
human embryonic kidney cells. In perforated patch clamp recordings, haloperidol blocks N-type calcium channels with an inhibition
constant of 120 μM. Upon internal dialysis with chloride containing pipette solution, the blocking affinity increases by 40-fold.
This effect could be attributed in part to the presence of internal chloride ions, as replacement of intracellular chloride
with methanesulfonate reduced haloperidol blocking affinity by almost one order of magnitude. Tonic inhibition of N-type channels
by Gβγ subunits further enhanced the blocking effects of haloperidol, suggesting the possibility of direct effects of Gβγ binding on the local environment of the piperidine receptor site. Overall, depending on the cytoplasmic environment experienced
by the channel, the blocking affinity of N-type calcium channels for haloperidol may vary by more than two orders of magnitude.
Thus, absolute blocking affinities at the piperidine receptor site must be interpreted cautiously and in the context of the
particular experimental setting.
Received: 23 July 1998/Revised: 19 October 1998 相似文献
3.
General diffusion pores and specific porin channels from outer membranes of gram-negative bacteria were reconstituted into
lipid bilayer membranes. The current noise of the channels was investigated for the different porins in the open state and
in the ligand-induced closed state using fast Fourier transformation. The open channel noise exhibited 1/f-noise for frequencies up to 200 Hz. The 1/f-noise was investigated using the Hooge formula (Hooge, Phys. Lett.
29A: 139–140 (1969)), and the Hooge parameter α was calculated for all bacterial porins used in this study. The 1/f-noise was in part caused by slow inactivation and activation of porin channels. However, when care was taken that during
the noise measurement no opening or closing of porin channels occurred, the Hooge Parameter α was a meaningful number for a given channel. A linear relationship was observed between α and the single-channel
conductance, g, of the different porins. This linear relation between single-channel conductance and the Hooge parameter α could be qualitatively explained by assuming that the passing of an ion through a bacterial porin channel is—to
a certain extent—influenced by nonlinear effects between channel wall and passing ion.
Received: 8 May 1996/Revised: 27 January 1997 相似文献
4.
S.I. Ortiz-Miranda J.A. Lasalde P.A. Pappone M.G. McNamee 《The Journal of membrane biology》1997,158(1):17-30
We studied the functional effects of single amino acid substitutions in the postulated M4 transmembrane domains of Torpedo californica nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus oocytes at the single-channel level. At low ACh concentrations and cold temperatures, the replacement of wild-type α418Cys
residues with the large, hydrophobic amino acids tryptophan or phenylalanine increased mean open times 26-fold and 3-fold,
respectively. The mutation of a homologous cysteine in the β subunit (β447Trp) had similar but smaller effects on mean open
time. Coexpression of α418Trp and β447Trp had the largest effect on channel open time, increasing mean open time 58-fold.
No changes in conductance or ion selectivity were detected for any of the single subunit amino acid substitutions tested.
However, the coexpression of the α418Trp and β447Trp mutated subunits also produced channels with at least two additional
conductance levels. Block by acetylcholine was apparent in the current records from α418Trp mutants. Burst analysis of the
α418Trp mutations showed an increase in the channel open probability, due to a decrease in the apparent channel closing rate
and a probable increase in the effective opening rate. Our results show that modifications in the primary structure of the
α- and β subunit M4 domain, which are postulated to be at the lipid-protein interface, can significantly alter channel gating,
and that mutations in multiple subunits act additively to increase channel open time.
Received: 27 September 1996/Revised: 28 January 1997 相似文献
5.
Dynamic Diversification from a Putative Common Ancestor of Scorpion Toxins Affecting Sodium, Potassium, and Chloride Channels 总被引:11,自引:1,他引:10
Oren Froy Tal Sagiv Michal Poreh Daniel Urbach Noam Zilberberg Michael Gurevitz 《Journal of molecular evolution》1999,48(2):187-196
Scorpions have survived successfully over millions of years without detectable changes in their morphology. Instead, they
have developed an efficient alomonal machinery and a stinging device supporting their needs for prey and defense. They produce
a large variety of polypeptidic toxins that bind and modulate ion channel conductance in excitable tissues. The binding site,
mode of action, and chemical properties of many toxins have been studied extensively, but little is known about their genomic
organization and diversity. Genes representing each of the major classes of Buthidae scorpion toxins, namely, ``long' toxins,
affecting sodium channels (alpha, depressant, and excitatory), and ``short' toxins, affecting potassium and chloride channels,
were isolated from a single scorpion segment and analyzed. Each toxin type was found to be encoded by a gene family. Regardless
of toxin length, 3-D structure, and site of action, all genes contain A+T-rich introns that split, at a conserved location,
an amino acid codon of the signal sequence. The introns vary in length and sequence but display identical boundaries, agree
with the GT/AG splice junctions, and contain T-runs downstream of a putative branch point, 5′-TAAT-3′. Despite little sequence
similarity among all toxin classes, the conserved gene organization, intron features, and common cysteine-stabilized α-helical
(CSH) core connecting an α-helix to a three-stranded β-sheet suggest, that they all evolved from an ancestral common progenitor.
Furthermore, the vast diversity found among genomic copies, cDNAs, and their protein products for each toxin suggests an extensive
evolutionary process of the scorpion ``pharmaceutical factory,' whose success is due, most likely, to the inherent permissiveness
of the toxin exterior to structural alterations.
Received: 16 March 1998 / Accepted: 30 July 1998 相似文献
6.
Hong Xue 《Journal of molecular evolution》1998,47(3):323-333
The gene superfamily of ligand-gated ion channel (LGIC) receptors is composed of members of excitatory LGIC receptors (ELGIC)
and inhibitory LGIC receptors (ILGIC), all using amino acids as ligands. The ILGICs, including GABAA, Gly, and GluCl receptors, conduct Cl− when the ligand is bound. To evaluate the phylogenetic relationships among ILGIC members, 90 protein sequences were analyzed
by both maximum-parsimony and distance matrix-based methods. The strength of the resulting phylogenetic trees was evaluated
by means of bootstrap. Four major phylogenetic branches are recognized. Branch I, called BZ, for the majority of the members
are known to be related to benzodiazepine binding, is subdivided into IA, composed of all GABAA receptor α subunits, and IB, composed of the γ and ε subunits, which are shown to be tightly linked. Branch II, named NB
for non–benzodiazepine binding, and consisting of GABAA receptor β, δ, π, and ρ subunits, is further subdivided into IIA, containing β subunits; IIB, containing δ, and π subunits;
and IIC, containing ρ subunits. Branch IIIA, composed of vertebrate Gly receptors, is loosely clustered with Branch IIIB,
composed of invertebrate GluCl receptors, to form Branch III, which is designated NA for being non–GABA responsive. Branch
IV is called UD for being undefined in specificity. The existence of primitive forms of GABAA receptor non-β subunits in invertebrates is first suggested by the present analysis, and the identities of sequences p25123
from Drosophila melanogaster, s34469 from Lymnaea stagnalis, and u14635 and p41849 from C. aenorhabditis elegans are determined to be different from their previously given annotations. The proposed branching classification of ILGICs provides
a phylogenetic map, based on protein sequences, for tracing the evolutionary pathways of ILGIC receptor subunits and determining
the identities of newly discovered subunits on the basis of their protein sequences.
Received: 15 April 1997 / Accepted: 11 March 1998 相似文献
7.
F. Anne Stephenson 《The Journal of biological chemistry》2012,287(48):40205-40206
The year 2012 marks the 25th anniversary of the discovery of the Cys loop ligand-gated ion channel superfamily of neurotransmitter receptors. This minireview series celebrates this with a series of articles reviewing current information for each of the family members, nicotinic acetylcholine receptors, glycine receptors, GABAA receptors, serotonin-3 (5-HT3) receptors, and glutamate-gated chloride ion channels of proteasome invertebrate phyla. 相似文献
8.
To determine the origin and evolutionary significance of a recently discovered isoform of the estrogen receptor (ERβ), we
examined the phylogenetic relationship of ERβ to the well-known α isoform (ERα) and other steroid receptors. Our phylogenetic
analyses traced the origin of ERβ to a single duplication event at least 450 million years ago. Since this duplication, the
evolution of both ER isoforms has apparently been constrained such that 80% of the amino acid positions in the DNA binding
domain (DBD) and 53% of the ligand binding domain (LBD) have remained unchanged. Using the phylogenetic tree, we determined
the amount of evolutionary change that had occurred in two ER isoforms. The DBD and the LBD had lower rates of evolutionary
change compared to the NH2 terminal domain. However, even with strong selective constraints on the DBD and LBD, our phylogenetic analyses demonstrate
two clearly separate phylogenetic histories for ERα and ERβ dating back several hundred million years. The ancient duplication
of ER and the parallel evolution of the two ER isoforms suggest that, although ERα and ERβ share a substantial degree of sequence
identity, they play unique roles in vertebrate physiology and reproduction.
Received: 19 January 1999 / Accepted: 26 May 1999 相似文献
9.
10.
Saier MH 《The Journal of membrane biology》2000,175(3):165-180
Channel-forming proteins/peptides fall into over 100 currently recognized families, most of which are restricted to prokaryotes
or eukaryotes, but a few of which are ubiquitous. These proteins fall into three major currently recognized classes: (i) α-helix-type
channels present in bacterial, archaeal and eukaryotic cytoplasmic and organellar membranes, (ii) β-barrel-type porins present
in the outer membranes of Gram-negative bacterial cells, mitochondria and chloroplasts, and (iii) protein/peptide toxins targeted
to the cytoplasmic membranes of cells other than those that synthesize the toxins. High-resolution 3-dimensional structural
data are available for representative proteins/peptides of all three of these channel-forming types. Each type exhibits distinctive
features that distinguish them from the other channel protein types and from carriers. Structural, functional, and evolutionary
aspects of transmembrane channel-formers are discussed.
Received: 10 September 1999/Revised: 11 February 2000 相似文献
11.
Evolution of the Integrin α and β Protein Families 总被引:4,自引:0,他引:4
Hughes AL 《Journal of molecular evolution》2001,52(1):63-72
A phylogenetic analysis of vertebrate and invertebrate α integrins supported the hypothesis that two major families of vertebrate
α integrins originated prior to the divergence of deuterostomes and protostomes. These two families include, respectively,
the αPS1 and αPS2 integrins of Drosophila melanogaster, and each family has duplicated repeatedly in vertebrates but not in Drosophila. In contrast, a third family (including αPS3) has duplicated in Drosophila but is absent from vertebrates. Vertebrate αPS1 and αPS2 family members are found on human chromosomes 2, 12, and 17. Linkage
of these family members may have been conserved since prior to the origin of vertebrates, and the two genes duplicated simultaneously.
A phylogenetic analysis of β integrins did not clearly resolve whether vertebrate β integrin genes duplicated prior to the
origin of vertebrates, although it suggested that at least the gene encoding vertebrate β4 may have done so. In general, the
phylogeny of neither α nor β integrins showed a close correspondence with patterns of α–β heterodimer formation or other functional
characteristics. One major exception to this trend involved αL, αM, αX, and αD, a monophyletic group of immune cell-expressed
α integrins, which share a number of common functional characteristics and have evolved in coordinated fashion with their
β integrin partners.
Received: 22 June 2000 / Accepted: 11 September 2000 相似文献
12.
Using the whole-cell patch-clamp technique, the selectivity and pharmacology of 8-Br-cGMP-stimulated currents in the human
alveolar cell line A549 was compared to 8-Br-cGMP-stimulated currents in HK293 cells transfected with hαCNC1. Whole cell currents
stimulated by 8-Br-cGMP in HK293 cells transfected with hαCNC1 or A549 cells are carried by inward sodium and outward potassium
with nearly the same selectivity. The whole-cell inward currents that are stimulated by 8-Br-cGMP in HK293 cells transfected
with hαCNC1 are inhibited by l-cis-diltiazem with an IC50 of 154 μm, by 2′,4′-dichlorobenzamil with an IC50 of 50 μm and by amiloride with an IC50 of 133 μm. The whole-cell inward currents in A549 cells that are stimulated by 8-Br-cGMP, are inhibited by l-cis-diltiazem with an
IC50 of 87 μm, by 2′4′-dichlorobenzamil with an IC50 of 38 μm and by amiloride with an IC50 of 32 μm suggesting that these airway cells contain cyclic nucleotide-gated cation channels. RT-PCR data suggest that mRNA of both
αCNC1 and βCNC subunits are present in A549 cells and the presence of the βCNC subunit, may as previously reported, increase
the affinity of these channel blockers compared to the hαCNC1 subunit alone. The mRNA of two other isoforms of this channel,
CNC2 and CNC3, are also expressed in the A549 cell line. This study documents the IC50 of externally applied channel blockers that can be used for in vitro or in vivo experiments to document sodium absorption
via cyclic nucleotide-gated cation channels in airway cells.
Received: 24 February/Revised: 28 May 1999 相似文献
13.
Adrian J. Wolstenholme 《The Journal of biological chemistry》2012,287(48):40232-40238
Glutamate-gated chloride channels (GluCls) are found only in protostome invertebrate phyla but are closely related to mammalian glycine receptors. They have a number of roles in these animals, controlling locomotion and feeding and mediating sensory inputs into behavior. In nematodes and arthropods, they are targeted by the macrocyclic lactone family of anthelmintics and pesticides, making the GluCls of considerable medical and economic importance. Recently, the three-dimensional structure of a GluCl was solved, the first for any eukaryotic ligand-gated anion channel, revealing a macrocyclic lactone-binding site between the channel domains of adjacent subunits. This minireview will highlight some unique features of the GluCls and illustrate their contribution to our knowledge of the entire Cys loop ligand-gated ion channel superfamily. 相似文献
14.
The G-protein-gated inwardly rectifying K
+(GIRK) family of ion channels form functional Gβγ-sensitive channels as heteromultimers of GIRK1 and either the GIRK2 or GIRK4
subunits. However, the homologous mouse brain GIRK3 clone failed to express in the earliest reported functional experiments
in Xenopus oocytes. We recloned the GIRK3 subunit from mouse brain and found that the new clone differed significantly from that originally
reported. The functional aspects of GIRK3 were reinvestigated by expression in CHO cells. The single channel properties of
GIRK1/GIRK3 were characterized and compared to those of the GIRK1/GIRK2 and GIRK1/GIRK4 channels. All three GIRK1/GIRKx combinations
produced channels with nearly indistinguishable conductances and kinetics. The response of GIRK1/GIRK3 to Gβγ in the 1–47
nm range was examined and found to be indistinguishable from that of GIRK1/GIRK4 channels. We conclude that GIRK1, with either
GIRK2, 3, or 4, gives rise to heteromultimeric channels with virtually identical conductances, kinetics, and Gβγ sensitivities.
Received: 13 January 1999/Revised: 2 March 1999 相似文献
15.
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
16.
J.I. Kourie 《The Journal of membrane biology》1999,167(1):73-83
The understanding of the role of cytoplasmic pH in modulating sarcoplasmic reticulum (SR) ion channels involved in Ca2+ regulation is important for the understanding of the function of normal and adversely affected muscles. The dependency of
the SR small chloride (SCl) channel from rabbit skeletal muscle on cytoplasmic pH (pH
cis
) and luminal pH (pH
trans
) was investigated using the lipid bilayer-vesicle fusion technique. Low pH
cis
6.75–4.28 modifies the operational mode of this multiconductance channel (conductance levels between 5 and 75 pS). At pH
cis
7.26–7.37 the channel mode is dominated by the conductance and kinetics of the main conductance state (65–75 pS) whereas
at low pH
cis
6.75–4.28 the channel mode is dominated by the conductance and kinetics of subconductance states (5–40 pS). Similarly, low
pH
trans
4.07, but not pH
trans
6.28, modified the activity of SCl channels. The effects of low pH
cis
are pronounced at 10−3 and 10−4
m [Ca2+]
cis
but are not apparent at 10−5
m [Ca2+]
cis
, where the subconductances of the channel are already prominent. Low pH
cis
-induced mode shift in the SCl channel activity is due to modification of the channel proteins that cause the uncoupling of
the subconductance states. The results in this study suggest that low pH
cis
can modify the functional properties of the skeletal SR ion channels and hence contribute, at least partly, to the malfunction
in the contraction-relaxation mechanism in skeletal muscle under low cytoplasmic pH levels.
Received: 20 May 1998/Revised: 24 September 1998 相似文献
17.
J.D.H. Bursell J. Kirk S.T. Hall A.M. Gero K. Kirk 《The Journal of membrane biology》1996,154(2):131-141
The unicellular protozoan parasite, Crithidia luciliae, responded to osmotic swelling by undergoing a regulatory volume decrease. This process was accompanied by the efflux of amino
acids (predominantly alanine, proline and glycine). The relative loss of the electroneutral amino acids proline, valine, alanine
and glycine was greater than that for the anionic amino acid, glutamate; there was negligible loss of the cationic amino acids,
lysine, arginine and ornithine. The characteristics of amino acid release were investigated using a radiolabeled form of the
nonmetabolized alanine analogue α-aminoisobutyrate. α-Aminoisobutyrate efflux was activated within a few seconds of a reduction
of the osmolality, and inactivated rapidly (again within a few seconds) on restoration of isotonicity. The initial rate of
efflux of α-aminoisobutyrate from cells in hypotonic medium was unaffected by the extracellular amino acid concentration.
Hypotonically activated α-aminoisobutyrate efflux (as well as the associated regulatory volume decrease) was inhibited by
the sulfhydryl reagent N-ethylmaleimide but was not inhibited by a range of anion transport blockers. As in the efflux experiments, unidirectional
influx rates for α-aminoisobutyrate increased markedly following reduction of the osmolality, consistent with the swelling-activated
amino acid release mechanism allowing the flux of solutes in both directions. Hypotonically activated α-aminoisobutyrate influx
showed no tendency to saturate up to an extracellular concentration of 50 mm. The functional characteristics of the amino acid release mechanism are those of a channel, with a preference for electroneutral
and anionic amino acids over cationic amino acids. However, the pharmacology of the system differs from that of the anion-selective
channels that are thought to mediate the volume-regulatory efflux of organic osmolytes from vertebrate cells.
Received: 13 May 1996/Revised: 9 July 1996 相似文献
18.
O.V. Krasilnikov J.B. Da Cruz L.N. Yuldasheva W.A. Varanda R.A. Nogueira 《The Journal of membrane biology》1998,161(1):83-92
This paper describes a new approach to evaluate the inner structure (including a main constriction and its localization)
of the water lumen of an ion channel. The method is based on the determination of channel filling by different nonelectrolyte
molecules through each side of an ion channel. The method has two characteristic features that make its use attractive: (i)
the possibility to ascertain the existence, localization and size of a narrow part inside an ion channel water lumen and (ii)
the chances to determine the maximal size of both entrances of an ion channel and to obtain additional information about the
geometry of its water lumen at the same time. Determinations were made on colicin Ia ion channels inserted into planar lipid
bilayers. This channel was chosen because there is an apparent contradiction between its low single channel conductance and
the large diameter of its water lumen. Our results show that the water lumen of the colicin Ia channel has a funnel-like structure
with a small trans-entrance, with a diameter of about 1.0 nm, and a large cis-entrance, with a diameter of approximately 1.8 nm. A constriction with a diameter of approximately 0.7 nm is shown to be
located close to the trans-entrance of the channel. The method can also be applied to patch clamp studies of single ion channels.
Received: 20 February 1997/Revised: 19 August 1997 相似文献
19.
Kirsch J 《Cell and tissue research》2006,326(2):535-540
Inhibition in the mature central nervous system is mediated by activation of γ-aminobutyric acid (GABAA) and glycine receptors. Both receptors belong to the same superfamily of ligand-gated ion channels and share common transmembrane topology and structural and functional features. Glycine receptors are pentameric ligand-gated anion channels composed of two different subunits, named α und β, that assemble with a fixed stoichiometric ratio of two α to three β subunits. Four genes encoding the α subunits exist, whereas only one gene encoding the β subunit has been detected. Ligand binding occurs at the interface of α and β subunits. The β subunit, which is unable to form homo-oligomeric receptors, is responsible for assembly and channel properties. Moreover, this subunit carries a binding motif for the cytoplasmic protein gephyrin, which is believed to mediate synaptic clustering and anchoring at inhibitory synapses by interacting with the subsynaptic cytoskeleton. Synaptic gephyrin appears to restrict the mobility of glycine receptors diffusing in the plane of the plasma membrane, thereby generating dynamic plasma membrane domains contributing to the plasticity of inhibitory synapses. Glycine receptors are well established as playing important roles in controlling motor functions and sensory signaling in vision and audition and those in the dorsal horn of the spinal cord are now considered to be new targets for pain therapies. Like GABAA receptors, glycine receptors have been shown to be depolarizing during development. The functional meaning of the developmental switch from excitatory to inhibitory glycine receptor action remains to be elucidated. 相似文献
20.
We observed intermediate conductance channels in approximately 20% of successful patch-clamp seals made on collecting tubules
dissected from Ambystoma adapted to 50 mm potassium. These channels were rarely observed in collecting tubules taken from animals which were maintained in tap water.
Potassium-adaptation either leads to an increase in the number of channels present or activates quiescent channels.
In cell-attached patches the conductance averaged 30.3 ± 2.4 (9) pS. Since replacement of the chloride in the patch pipette
with gluconate did not change the conductance, the channel carries cations, not anions. Notably, channel activity was observed
at both positive and negative pipette voltages. When the pipette was voltage clamped at 0 mV or positive voltages, the current
was directed inward, consistent with the movement of sodium into the cell. The pipette voltage at which the polarity of the
current reversed (movement of potassium into the pipette) was −29.6 ± 6.5(9) mV.
Open probability at 0 mV pipette voltage was 0.08 ± 0.03 and was unaffected when the apical membrane was exposed to either
2 × 10−6 or 2 × 10−5
m of amiloride. Exposure of the basolateral surface of the tubule to a saline containing 15 mm potassium caused a significant increase (P less than 0.001) in the open probability of these channels to 0.139 ± 0.002 without affecting the conductance of the apical
channel.
These data illustrate the presence of an intermediate conductance, poorly selective, amiloride-insensitive cation channel
in native vertebrate collecting tubule. We postulate that, at least in amphibia, this channel may be used to secrete potassium.
Received: 14 January 2000/Revised: 16 June 2000 相似文献