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Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina
Received October 11, 2002; accepted February 21, 2003
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Abstract |
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 Top Abstract Materials and MethodsResultsDiscussionReferences |
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50 pS. These
channels seem to be nonselective cation channels; monovalent cations are the
major carriers of current, but finite permeability to
Ca2+ leads to a significant intracellular
Ca2+ signal. Experiments with excised patches indicate
that 2-APB activates these channels from the outer aspect of the cell
membrane. This effect of 2-APB further illustrates the complex actions of this
compound and reveals the presence in RBL-2H3 m1 cells of a novel, ligand-gated
calcium-permeable channel.
). Accordingly, 2-APB has been used to investigate the role
of IP3 receptors in the regulation of capacitative calcium entry
(Ma et al., 2000) and other
processes (Maruyama et al.,
1997a; Ascher-Landsberg et al.,
1999; Wu et al.,
2000). Capacitative or store-operated calcium entry is a process
whereby the depletion of intracellular Ca2+ stores in
some manner signals the opening of Ca2+-permeable
channels in the plasma membrane (Putney,
1986,
1997). One proposed mechanism
for this signaling is the conformational coupling model, according to which
IP3 receptors on the endoplasmic reticulum in close proximity with
plasma membrane capacitative calcium entry channels interact with those
channels and, in response to a reduction in endoplasmic reticulum
Ca2+ content, signal their activation
(Irvine, 1990;
Berridge, 1995). The ability of
2-APB to inhibit capacitative calcium entry was originally interpreted as
supportive of the conformational coupling mechanism
(Ma et al., 2000). However,
subsequently we (Braun et al.,
2001) and others (Bakowski et
al., 2001; Dobrydneva and
Blackmore, 2001; Gregory et
al., 2001; Iwasaki et al.,
2001; Prakriya and Lewis,
2001) demonstrated that 2-APB inhibits capacitative calcium entry
channels at an extracellular site by a mechanism not involving IP3
receptors. 2-APB inhibits other channels as well, in particular the
Mg2+- or
Mg2+-ATP–inhibitable channels believed to be
encoded by LTRPC7/TRPM7 (Hermosura et al.,
2002; Kozak et al.,
2002; Prakriya and Lewis,
2002). In addition, low concentrations of 2-APB have been reported
to potentiate rather than inhibit capacitative calcium entry channels
(Prakriya and Lewis, 2001;
Ma et al., 2002). In the current study, we investigated the action of 2-APB in the mast cell line RBL-2H3 m1. We discovered that, in addition to its previously described actions, 2-APB activates a calcium-permeable cation channel in the plasma membrane by an action at the outer surface. This channel seems to be a novel, "orphan" ligand-gated channel that may be involved in the regulation of cellular cation fluxes by unknown extracellular factors.
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Materials and Methods |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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Fura-2 Loading and Fluorescence Measurements. Coverslips with attached cells were mounted in a Teflon chamber and incubated at room temperature for 30 min in culture medium containing 1 µM Fura-2 AM (Molecular Probes, Eugene, OR). Cells were then washed and bathed in HEPES-buffered saline solution (140 mM NaCl, 10 mM KCl, 2 mM CaCl2, 1 mM MgCl2, and 10 mM HEPES, pH 7.2) for at least 15 min before Ca2+ measurements were made.
Fluorescence was monitored by placing the Teflon chamber with the coverslip of Fura-2–loaded cells onto the stage of a Nikon Diaphot microscope (40x Neofluor objective; Nikon, Melville, NY). Cells were excited alternately by light (340 and 380 nm) from a Deltascan D101 (Photon Technology International, Monmouth Junction, NJ) light source equipped with a filter changer. Emitted fluorescence (510 nm) was collected by a photomultiplier tube (Omega Optical, Brattleboro, VT). All experiments were conducted at room temperature (20 to 22°C). All measurements shown are means ± S.E.M. or are representative of a minimum of three independent experiments.
Electrophysiology. Patch-clamp experiments were performed at 20 to 22°C in the tight-seal whole-cell and cell-attached configurations. Patch pipettes were pulled from borosilicate glass (Corning glass, 7052; Corning Glassworks, Corning, NY) and fire-polished. Membrane currents, filtered at 1 to 2 kHz, were recorded using an Axopatch-200B amplifier (Axon Instruments Inc., Union City, CA). Voltage-clamp protocols were implemented, and data acquisition was performed with pCLAMP 8.2 software (Axon Instruments). Solution changes were accomplished by bath perfusion. All voltages for creating I-V curves were corrected for liquid junction potential.
For whole-cell experiments with Ca2+ as the charge
carrier, unless stated otherwise, the patch pipette (2 to 5 M
) solution
had the following composition: 140 mM Cs+ aspartate, 2 mM
MgCl2, 1 mM MgATP, 10 mM Cs+-BAPTA (with free calcium
set to 100 nM, calculated using MaxChelator software, version 6.60), and 10 mM
HEPES; pH adjusted to 7.2 with CsOH. The bath solution contained 140 mM NaCl,
4.7 mM KCl, 10 mM CsCl, 1.13 mM MgCl2, 10 mM glucose, 10 mM
CaCl2, and 10 mM HEPES; pH adjusted to 7.2 with NaOH. In
experiments examining monovalent and divalent selectivity of
2-APB–activated channels (Fig.
6A), the NaCl was increased to 150 mM, and KCl, CsCl, and
MgCl2 were omitted from the bath solution. Divalent-free bath
solutions, with Na+ as the charge carrier, contained 150 mM
Na+ methane sulfonate or NaCl, 2 mM EDTA, and and 10 mM HEPES; pH
adjusted to 7.2 with NaOH. CRAC channels were opened by passive
store-depletion with 1 µM thapsigargin added to the bath. Cells were held
at a potential of 0 mV. Every 1, 2, or 5 s, either voltage ramps from
—100 to +60 mV or voltage steps from 0 to —100 mV were delivered
for 200 ms. Currents were sampled at 5 kHz during voltage ramps and at 25 kHz
during voltage steps.
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) solutions contained 150 mM NaCl, 2 mM EDTA, and 10 mM HEPES, pH 7.2
(with NaOH). The bath solutions contained 145 mM KCl, 5 mM NaCl, 10 mM
MgCl2, and 10 mM HEPES, pH 7.2 (with KOH) to nullify the cell's
resting potential. When patches were excised, the bath solutions contained 145
mM K-glutamate, 5 mM NaCl, 2 mM EDTA, and 10 mM HEPES. Single-channel analysis
was performed with the pCLAMP 6 software. Po values were
calculated for 10- (Fig. 8) and
60-s (Fig. 7) periods according
to the relationship
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Materials. Thapsigargin was from LC laboratories (Woburn, MA). Cs4-BAPTA and Fura-2 were from Molecular Probes. 2-APB was purchased from Paradigm Organics (Raleigh, NC).
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Results |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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). In the
presence of 2 mM Ca2+ in the bath, the increase in
intracellular Ca2+ concentration
([Ca2+]i) on thapsigargin addition was
biphasic because of Ca2+ release from internal stores
followed by Ca2+ influx through capacitative calcium
entry channels (Takemura et al.,
1989) (Fig. 1A; see
also Fig. 2B wherein
thapsigargin-induced release and entry are separated with the use of a
capacitative calcium entry blocker, Gd3+).
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As shown in Fig. 1, the
application of 2-APB inhibited capacitative calcium entry in RBL-2H3 m1 cells
in a concentration-dependent manner. Low doses of 2-APB, 6.25 µM
(Fig. 1A) and 25 µM
(Fig. 1B), caused a transient
elevation of [Ca2+]i preceding the inhibitory
phase, with the lowest concentration producing a more pronounced potentiation
of Ca2+ influx. This potentiation of influx by low
concentrations of 2-APB is caused by augmentation of capacitative calcium
influx, as reported previously by others
(Prakriya and Lewis, 2001;
Ma et al., 2002). A
concentration of 25 µM 2-APB was able to fully inhibit
Ca2+ entry and bring the
[Ca2+]i back to baseline within 250 s
(Fig. 1B). Within the same time
frame of 250 s after the addition of 2-APB, concentrations of this drug lower
than and unexpectedly also greater than 25 µM resulted in incomplete
inhibition (Fig. 1, A, C, and
D). A possible explanation for the incomplete inhibition at higher
concentrations of 2-APB could be that in addition to inhibiting capacitative
calcium entry channels, higher concentrations of 2-APB may inhibit
Ca2+ extrusion. However, if higher concentrations of
2-APB were to block Ca2+-extrusion, then the decay times
of [Ca2+]i would be increased. From the
results in Fig. 1 precisely the
opposite was observed; the t1/2 after 25 µM 2-APB was
27 s versus 14 s after100 µM 2-APB.
To address the nature of the residual
[Ca2+]i elevation in response to 2-APB, we
examined the effects of 2-APB on [Ca2+]i in
the absence of capacitative calcium entry. For the experiments shown in
Fig. 2A, the same protocol was
used as for Fig. 1, except that
all solutions contained 1 µM Gd3+ to inhibit
capacitative calcium entry (Broad et al.,
1999; Luo et al.,
2001). In the presence of Gd3+, although
Ca2+ was included in the bath, thapsigargin-addition now
resulted only in a transient increase in
[Ca2+]i, caused by Ca2+
release from intracellular stores. Challenging the cells subsequently with
6.25 µM 2-APB did not cause any increase in
[Ca2+]i, indicating that the response seen in
Fig. 1 at this concentration
results from capacitative calcium entry. However, 100 µM 2-APB caused a
significant increase in [Ca2+]i that was
insensitive to Gd3+. The level of
[Ca2+]i reached after the addition of 2-APB,
with capacitative calcium entry channels blocked by
Gd3+, was similar to the level of
[Ca2+]i when capacitative calcium entry was
fully blocked by 2-APB, in the absence of Gd3+
(Fig. 2B). Therefore, what
seemed to be incomplete inhibition of capacitative calcium entry at
supra-maximal concentrations of the inhibitor 2-APB results from simultaneous
activation of a [Ca2+]i increase by 2-APB,
which is independent of calcium flux through capacitative calcium entry
channels.
2-APB Activates Ca2+-Permeable Channels in the Plasma Membrane Independently of Store Depletion. We next attempted to determine the source of the intracellular Ca2+ increase activated by the addition of 2-APB. Figure 3 shows that after the discharge of Ca2+ stores by thapsigargin and in the absence of extracellular Ca2+, 2-APB does not cause any detectable Ca2+ release. This indicates that 2-APB does not release Ca2+ from thapsigargin-insensitive stores and that the 2-APB [Ca2+]i signal depends on extracellular Ca2+.
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The most likely scenario is that 2-APB activates Ca2+ channels in the plasma membrane independently of store depletion. To further establish independence of store depletion, 100 µM 2-APB was added to cells with and without prior store depletion. For this experiment, we depleted stores by incubating the cells for 11 min in Ca2+-free buffer with 2 mM EDTA added. This depletion protocol resulted in robust Ca2+ entry when Ca2+ was restored to the bath (Fig. 4A). This Ca2+ entry was genuine capacitative calcium entry because it was inhibited by 1 µM Gd 3+ (control + Gd 3+). With Gd3+ present to prevent the activation of capacitative calcium entry, the addition of 2-APB along with Ca2+ activated Ca2+ entry that was indistinguishable in the presence or absence of prior store-depletion (Fig. 4B).
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Currents through Capacitative Calcium Entry Channels and
2-APB–Activated Channels. We first used the whole-cell recording
configuration of the patch-clamp technique to establish that >50 µM
2-APB indeed activates a store-depletion–independent conductance across
the plasma membrane. The results of the
[Ca2+]i measurements predict that the channel
activity and properties induced by 2-APB should be the same with or without
prior store depletion. The results depicted in
Fig. 5 confirm that this is
indeed the case, and they lead to a few interesting observations. First, in a
modified Ringer solution containing 10 mM Ca2+,
capacitative calcium entry currents (Icrac)
(Hoth and Penner, 1992) showed
the well-described development upon thapsigargin-addition, and as shown
previously (Braun et al., 2001)
100 µM 2-APB was able to inhibit this current
(Fig. 5A). However, the
inhibition of capacitative calcium entry channels seemed incomplete,
consistent with the findings shown in Figs.
1,
2,
3,
4. The residual and somewhat
unstable current after 2-APB addition (plus thapsigargin trace) showed
behavior similar to the current activated by treating the cells with 2-APB
alone (without thapsigargin trace). In both cases, after the addition of
2-APB, single channel openings were observed
(Fig. 5B), and these channels
had an average slope conductance of 40 pS
(Fig. 5, C and D). These
channels were not activated by an intracellular Ca2+
increase because the cytoplasmic solution in the pipette was strongly clamped
to 100 nM [Ca2+]i with 10 mM BAPTA. The
2-APB–activated single channels could easily be resolved in the
whole-cell configuration, indicating either a low number of those channels per
cell or channels that have a low open probability under these conditions. The
latter explanation is favored by the fact that similar channels were seen in
the majority of measurements in the cell-attached configuration
(Fig. 9).
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The observation of 2-APB–activated single-channel events in the
whole-cell configuration explains the rather unstable pattern of measured
current values plotted versus time compared with the more stable
Icrac (Fig.
5A). During Icrac development, thousands of
channels having a very small conductance of approximately 0.2 pS but with high
open probability opened sequentially
(Prakriya and Lewis,
2002).
Na+ Is the Main Charge Carrier through
2-APB–Activated Channels. The next step was to determine the
permeability of the 2-APB–activated channels for
Ca2+, because the addition of 2-APB at concentrations
greater than 50 µM always caused a significant increase in
[Ca2+]i, as measured with the
Ca2+ indicator dye Fura-2 (Figs.
1,
2,
3,
4). The addition of 100 µM
2-APB to cells bathed in Ringer's solution containing 10 mM
Ca2+ resulted in immediate single-channel events with a
channel conductance of 40 pS (Fig. 6, A and
B), as established in Fig.
5. When the Na+ ions in the bath were substituted with
the impermeable cation N-methyl-D-glucamine (NMDG),
leaving all the other ions unchanged, single-channel currents were no longer
detectable (Fig. 6B). This
indicates that the channels mainly conduct monovalent cations. However, the
Fura-2 experiments indicate sufficient Ca2+ permeability
to increase [Ca2+]i measurably, suggesting
that under physiological conditions the Ca2+ conductance
of the channels is small but finite and is only detectable with
Ca2+-indicating dyes (Figs.
1,
2,
3,
4). In support of this
conclusion, in the presence of an NMDG-substituted extracellular solution, no
current is detected, yet Ca2+ entry is still observed
(Fig. 6C). We attempted
measurement of Ca2+ currents with isotonic
Ca2+ solutions, but we still could not observe single
channels (data not shown); however, extracellular Ca2+
seems to negatively regulate these channels (see below). Thus, the inability
to observe measurable current carried by Ca2+ does not
necessarily mean that Ca2+ does not permeate the
channels; for example, in the case of the store-operated channels underlying
Icrac, it is possible to produce sufficient
Ca2+ entry to increase
[Ca2+]i significantly, yet no associated
current is detected. Only strategies that reduce feedback inhibition of CRAC
channels result in detectable current
(Huang et al., 1998).
Because Na+ seems to be the main ion passing through 2-APB–activated channels, we next determined whether divalent cations might influence or regulate Na+ conductance of the channels. When all divalent cations were omitted from the bath solution, single channels with an average conductance of 170 pS were activated immediately upon 2-APB addition, and this effect was rapidly reversed after the removal of 2-APB (Fig. 6, D and E). We next compared the appearance of 2-APB–activated channels in bath solutions containing 2 mM Ca2+, containing no added divalent cations but without a divalent chelator present, and containing no added divalent cations plus 2 mM EDTA. As shown in Fig. 7, with decreasing concentrations of divalent cations in the bath, the conductance, as well as the open probability of the channels, increased. The open probabilities with 2 mM Ca2+ and with no divalent cations added to the bath (which equals approximately 10 µM Ca2+) were not significantly different. However, the reduction of divalent cations to very low levels with EDTA resulted in an approximately 4-fold increase in open probability (Fig. 7B). The conductance of the channels is even more closely connected to the presence of extracellular divalent cations. The conductance more than tripled from 50 to 165 pS when the bath was switched from a solution containing 2 mM Ca2+ to a bath that was free of divalent cations (Fig. 7C). However, in all cases, the I-V relationships remained linear and crossed the voltage axis near 0 mV.
From the demonstrated Na+ permeability (Fig. 6), the Ca2+ increases in the Fura-2 measurements (Fig. 1, 2, 3, 4), as well as the linear I-V curves with reversal potentials of approximately 0 mV with and without extracellular Ca2+ (Figs. 5D and 7C), the 2-APB–activated channels seem to be Ca2+-permeable nonselective cation channels.
Sensitivity of the Channels to 2-APB. We next addressed the dose-response properties of the channels for 2-APB. These experiments were carried out in divalent cation-free bath solutions to take advantage of the larger Na+ conductance. The goal was to compare the results from these measurements with those for 2-APB–activated intracellular Ca2+ increases in Fura-2 experiments, as shown in Fig. 1. When the open probability of the channels, conducting Na+, was examined as a function of increasing concentrations of 2-APB (Fig. 8), the concentrations of 2-APB activating the single channels were found to be similar to those that activated Ca2+ influx measured with Fura-2 (Fig. 1). 2-APB (50 µM) was a threshold concentration to observe the stimulatory effect on the channels. 2-APB (100 µM) resulted in an approximate 4-fold increase in influx under conditions in which the release of Ca2+ by 2-APB was still minimal. Concentrations of greater than 100 µM 2-APB were not examined because Ca2+ release becomes more prominent in this range (data not shown). The similarity of the thresholds of 2-APB concentration for activating Na+ currents and Ca2+ influx suggest that the same channels underlie both phenomena.
We also observed the activation of single channels by 2-APB in the
cell-attached mode (Fig. 9). In
these experiments, the pipette contained 100 µM 2-APB, and single-channel
activity was observed in 15 of 16 experiments. When 2-APB was not included in
the pipette, channels were never seen (>100 experiments). After excision of
the 2-APB–treated patches, activity was maintained for several minutes,
although often at a somewhat diminished open probability. In seven experiments
in which 2-APB was added outside of the pipette after establishing the cell
attached configuration, five cells showed no channel activity and two showed
channels with very low open probability that appeared after a very long
latency (minutes). In 14 of the excised patches and to which 2-APB was added
after excision to the cytoplasmic side of the membrane, 2-APB–activated
channels were never seen; rather, the low divalent cation conditions led to
the appearance of lower-conducting (40 pS) channels (data not shown)
(Braun et al., 2001) believed
to reflect MagNuM/MIC channels (Hermosura
et al., 2002).
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Discussion |
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TopAbstractMaterials and MethodsResultsDiscussionReferences |
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Two other important channels that have been shown to be modulated by 2-APB
are CRAC channels (Hoth and Penner,
1992; Braun et al.,
2001) and the Mg2+- or
Mg2+-ATP–regulated MagNuM/MIC channels
(Nadler et al., 2001;
Runnels et al., 2001;
Hermosura et al., 2002;
Kozak et al., 2002;
Prakriya and Lewis, 2002).
Both of these channels are inhibited by 2-APB, and CRAC channels can also be
potentiated at low concentrations of 2-APB. We observed these actions of 2-APB
in RBL cells, including the inhibition of Icrac
(Braun et al., 2001;
Broad et al., 2001),
potentiation of Icrac
(Fig. 1), and inhibition of
MagNuM/MIC (Braun et al.,
2001). In the latter case, we originally described the inhibition
by 2-APB of channels observed in the absence of divalent cations that we
believed were CRAC channels; however, recent findings indicate that these
channels are more likely to be MagNuM/MIC channels
(Hermosura et al., 2002;
Kozak et al., 2002;
Prakriya and Lewis, 2002). It
is clear that the channels observed in the current study activated by higher
concentrations of 2-APB are distinct from both CRAC and MagNuM/MIC channels.
The distinct properties of the three channel types are summarized in
Table 1. There are reports of
other cation-permeable channels in mast cells or RBL cell lines
(Fasolato et al., 1993;
Obukhov et al., 1995).
However, none has the single-channel conductance, current-voltage
relationship, or other properties found for the 2-APB–activated
channels. Therefore we conclude that the action of this drug has revealed the
presence of a previously undetected cation channel capable of significant
regulation of cation fluxes and/or Ca2+ signaling. The
challenge for future work is to determine the regulator or regulators and the
physiological function of this channel in RBL and mast cells.
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Acknowledgements |
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Footnotes |
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Address correspondence to: Dr. James W. Putney, Jr., National Institute of Environmental Health Sciences, P.O. Box 12233, Research Triangle Park, NC 27709. E-mail: putney{at}niehs.nih.gov
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References |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Bakowski D, Glitsch MD, and Parekh AB (2001) An
examination of the secretion-like coupling model for the activation of the
Ca2+ release-activated Ca2+
current Icrac in RBL-1 cells. J Physiol (Lond)
532:
55–71.
Berridge MJ (1995) Capacitative calcium entry. Biochem J 312: 1–11.
Braun F-J, Broad LM, Armstrong DL, and Putney JW Jr
(2001) Stable activation of single CRAC-channels in divalent
cation-free solutions. J Biol Chem
276:
1063–1070.
Broad LM, Braun F-J, Lièvremont J-P, Bird G St J, Kurosaki
T, and Putney JW Jr (2001) Role of the phospholipase C-inositol
1,4,5-trisphosphate pathway in calcium release-activated calcium current
(Icrac) and capacitative calcium entry. J Biol
Chem 276:
15945–15952.
Broad LM, Cannon TR, and Taylor CW (1999) A
non-capacitative pathway activated by arachidonic acid is the major
Ca2+ entry mechanism in rat A7r5 smooth muscle cells
stimulated with low concentrations of vasopressin. J Physiol
(Lond) 517:
121–134.
Dobrydneva Y and Blackmore P (2001)
2-Aminoethoxydiphenyl borate directly inhibits store-operated calcium entry
channels in human platelets. Mol Pharmacol
60:
541–552.
Fasolato C, Hoth M, Matthews G, and Penner R (1993)
Ca2+ and Mn2+ influx through
receptor-mediated activation of nonspecific cation channels in mast cells.
Proc Natl Acad Sci USA
90:
3068–3072.
Gregory RB, Rychkov G, and Barritt GJ (2001) Evidence that 2-aminoethyl diphenylborate is a novel inhibitor of store-operated Ca2+ channels in liver cells and acts through a mechanism which does not involve inositol trisphosphate receptors. Biochem J 354: 285–290.[CrossRef][Medline]
Hermosura MC, Monteilh-Zoller MK, Scharenberg AM, Penner R, and
Fleig A (2002) Dissociation of the store-operated calcium current
Icrac and the Mg-nucleotide-regulated metal ion current MagNuM. J
Physiol (Lond) 539:
445–458.
Hoth M and Penner R (1992) Depletion of intracellular calcium stores activates a calcium current in mast cells. Nature (Lond) 355: 353–355.[CrossRef][Medline]
Huang Y, Takahashi M, Tanzawa K, and Putney JW Jr
(1998) Effect of adenophostin A on Ca2+
entry and calcium release-activated calcium current
(Icrac) in rat basophilic leukemia cells. J
Biol Chem 273:
31815–31821.
Irvine RF (1990) "Quantal" Ca2+ release and the control of Ca2+ entry by inositol phosphates—a possible mechanism. FEBS Lett 263: 5–9.[CrossRef][Medline]
Iwasaki H, Mori Y, Hara Y, Uchida K, Zhou H, and Mikoshiba K (2001) 2-Aminoethoxydiphenyl borate (2-APB) inhibits capacitative calcium entry independently of the function of inositol 1,4,5-trisphosphate receptors. Recept Channels 7: 429–439.[Medline]
Kozak JA, Kerschbaum HH, and Cahalan MD (2002)
Distinct properties of CRAC and MIC channels in RBL cells. J Gen
Physiol 120:
221–235.
Luo D, Broad LM, Bird G St J, and Putney JW Jr (2001)
Signaling pathways underlying muscarinic receptor-induced
[Ca2+]i oscillations in HEK293 cells.
J Biol Chem 276:
5613–5621.
Ma H-T, Patterson RL, van Rossum DB, Birnbaumer L, Mikoshiba K, and
Gill DL (2000) Requirement of the inositol trisphosphate receptor
for activation of store-operated Ca2+ Channels.
Science (Wash DC) 287:
1647–1651.
Ma H-T, Venkatachalam K, Parys JB, and Gill DL (2002)
Modification of store-operated channel coupling and inositol trisphosphate
receptor function by 2-aminoethoxydiphenyl borate in DT40 lymphocytes.
J Biol Chem 277:
6915–6922.
Maruyama T, Cui ZJ, Kanaji T, Mikoshiba K, and Kanno T (1997a) Attenuation of intracellular Ca2+ and secretory responses by Ins(1,4,5)P3-induced Ca2+ release modulator, 2APB, in rat pancreatic acinar cells. Biomed Res 18: 297–307.
Maruyama T, Kanaji T, Nakade S, Kanno T, and Mikoshiba K
(1997b) 2APB, 2-aminoethoxydiphenyl borate, a membrane-penetrable
modulator of Ins(1,4,5)P3-induced Ca2+
release. J Biochem 122:
498–505.
Nadler MJS, Hermosura MC, Inabe K, Perraud A-L, Zhu Q, Stokes AJ, Kurosaki T, Kinet J-P, Penner R, Scharenberg AM, et al. (2001) LTRPC7 Is a Mg-ATP-regulated divalent cation channel required for cell viability. Nature (Lond) 411: 590–595.[CrossRef][Medline]
Obukhov AG, Jones S VP, Degtlar VE, Lückhoff A, Schultz G, and Hescheler J (1995) Ca2+-permeable large-conductance nonselective cation channels in rat basophilic leukemia cells. Am J Physiol 269: C1119–C1125.[Medline]
Prakriya M and Lewis RS (2001) Potentiation and
inhibition of Ca2+ release-activated
Ca2+ channels by 2-aminoethyldiphenyl borate (2-APB)
occurs independently of IP3 receptors. J Physiol
(Lond) 536:
3–19.
Prakriya M and Lewis RS (2002) Separation and
characterization of currents through store-operated CRAC channels and
Mg2+-inhibited cation (MIC) channels. J Gen
Physiol 119:
487–507.
Putney JW Jr (1986) A model for receptor-regulated calcium entry. Cell Calcium 7: 1–12.[CrossRef][Medline]
Putney JW Jr (1997) Capacitative Calcium Entry, Landes Biomedical Publishing, Austin, TX.
Runnels LW, Yue L, and Clapham DE (2001) TRP-PLIK, a
bifunctional protein with kinase and ion channel activities.
Science (Wash DC) 291:
1043–1047.
Takemura H, Hughes AR, Thastrup O, and Putney JW Jr
(1989) Activation of calcium entry by the tumor promoter,
thapsigargin, in parotid acinar cells. Evidence that an intracellular calcium
pool and not an inositol phosphate, regulates calcium fluxes at the plasma
membrane. J Biol Chem
264:
12266–12271.
Thastrup O (1990) Role of Ca2+-ATPases in regulation of cellular Ca2+ signalling, as studied with the selective microsomal Ca2+-ATPase inhibitor, thapsigargin. Agents Actions 29: 8–15.[CrossRef][Medline]
Wu J, Kamimura N, Takeo T, Suga S, Wakui M, Maruyama T, and Mikoshiba K (2000) 2-Aminoethoxydiphenyl borate modulates kinetics of intracellular Ca2+ stores in single pancreatic acinar cells of mouse. Mol Pharmacol 58: 1368–1374.
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B. J. Dewar, O. S. Gardner, C.-S. Chen, H. S. Earp, J. M. Samet, and L. M. Graves Capacitative Calcium Entry Contributes to the Differential Transactivation of the Epidermal Growth Factor Receptor in Response to Thiazolidinediones Mol. Pharmacol., November 1, 2007; 72(5): 1146 - 1156. [Abstract] [Full Text] [PDF]
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 D. Bai, C. del Corsso, M. Srinivas, and D. C. Spray Block of Specific Gap Junction Channel Subtypes by 2-Aminoethoxydiphenyl Borate (2-APB) J. Pharmacol. Exp. Ther., December 1, 2006; 319(3): 1452 - 1458. [Abstract] [Full Text] [PDF]
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|
 J. Huang, C. van Breemen, K.-H. Kuo, L. Hove-Madsen, and G. F. Tibbits Store-operated Ca2+ entry modulates sarcoplasmic reticulum Ca2+ loading in neonatal rabbit cardiac ventricular myocytes Am J Physiol Cell Physiol, June 1, 2006; 290(6): C1572 - C1582. [Abstract] [Full Text] [PDF]
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 |
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 M. Li, J. Jiang, and L. Yue Functional Characterization of Homo- and Heteromeric Channel Kinases TRPM6 and TRPM7 J. Gen. Physiol., April 24, 2006; 127(5): 525 - 537. [Abstract] [Full Text] [PDF]
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 A. Warrier, S. Borges, D. Dalcino, C. Walters, and M. Wilson Calcium From Internal Stores Triggers GABA Release From Retinal Amacrine Cells J Neurophysiol, December 1, 2005; 94(6): 4196 - 4208. [Abstract] [Full Text] [PDF]
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 Q. Gu, R.-L. Lin, H.-Z. Hu, M. X. Zhu, and L.-Y. Lee 2-Aminoethoxydiphenyl borate stimulates pulmonary C neurons via the activation of TRPV channels Am J Physiol Lung Cell Mol Physiol, May 1, 2005; 288(5): L932 - L941. [Abstract] [Full Text] [PDF]
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 M.-K. Chung, A. D. Guler, and M. J. Caterina Biphasic Currents Evoked by Chemical or Thermal Activation of the Heat-gated Ion Channel, TRPV3 J. Biol. Chem., April 22, 2005; 280(16): 15928 - 15941. [Abstract] [Full Text] [PDF]
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K. D. Garcia, T. Shah, and J. Garcia Immunolocalization of type 2 inositol 1,4,5-trisphosphate receptors in cardiac myocytes from newborn mice Am J Physiol Cell Physiol, October 1, 2004; 287(4): C1048 - C1057. [Abstract] [Full Text] [PDF]
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S. I. Zakharov, T. Smani, Y. Dobrydneva, F. Monje, C. Fichandler, P. F. Blackmore, and V. M. Bolotina Diethylstilbestrol Is a Potent Inhibitor of Store-Operated Channels and Capacitative Ca2+ Influx Mol. Pharmacol., September 1, 2004; 66(3): 702 - 707. [Abstract] [Full Text] [PDF]
|
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|
|
|
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H.-Z. Hu, Q. Gu, C. Wang, C. K. Colton, J. Tang, M. Kinoshita-Kawada, L.-Y. Lee, J. D. Wood, and M. X. Zhu 2-Aminoethoxydiphenyl Borate Is a Common Activator of TRPV1, TRPV2, and TRPV3 J. Biol. Chem., August 20, 2004; 279(34): 35741 - 35748. [Abstract] [Full Text] [PDF]
|
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|
|
 |
|
 M.-K. Chung, H. Lee, A. Mizuno, M. Suzuki, and M. J. Caterina 2-Aminoethoxydiphenyl Borate Activates and Sensitizes the Heat-Gated Ion Channel TRPV3 J. Neurosci., June 2, 2004; 24(22): 5177 - 5182. [Abstract] [Full Text] [PDF]
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J. H. Nam, J.-E. Woo, D.-Y. Uhm, and S. J. Kim Membrane-delimited Regulation of Novel Background K+ Channels by MgATP in Murine Immature B Cells J. Biol. Chem., May 14, 2004; 279(20): 20643 - 20654. [Abstract] [Full Text] [PDF]
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 G. Boddy, A. Bong, W. Cho, and E. E. Daniel ICC pacing mechanisms in intact mouse intestine differ from those in cultured or dissected intestine Am J Physiol Gastrointest Liver Physiol, April 1, 2004; 286(4): G653 - G662. [Abstract] [Full Text] [PDF]
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C. Zitt, B. Strauss, E. C. Schwarz, N. Spaeth, G. Rast, A. Hatzelmann, and M. Hoth Potent Inhibition of Ca2+ Release-activated Ca2+ Channels and T-lymphocyte Activation by the Pyrazole Derivative BTP2 J. Biol. Chem., March 26, 2004; 279(13): 12427 - 12437. [Abstract] [Full Text] [PDF]
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A. Shalabi, F. Zamudio, X. Wu, A. Scaloni, L. D. Possani, and M. L. Villereal Tetrapandins, a New Class of Scorpion Toxins That Specifically Inhibit Store-operated Calcium Entry in Human Embryonic Kidney-293 Cells J. Biol. Chem., January 9, 2004; 279(2): 1040 - 1049. [Abstract] [Full Text] [PDF]
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) activates Icrac, and this
current is inhibited by 100 µM 2-APB. The addition of 2-APB results in less
stable membrane current in both the presence and absence (
) of
thapsigargin. B, inspection of current records during steps to —100 mV
reveals unitary channel openings after the addition of 2-APB. C and D, from
current measurements at different voltages (C) the current-voltage
relationship (D) was constructed, which yielded a slope conductance of 40
pS.