Department of Physiology and Biophysics, University of Illinois at Chicago College of Medicine, Chicago, Illinois 60607
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ABSTRACT |
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The skeletal muscle L-type
calcium channel or dihydropyridine receptor (DHPR) plays an
integral role in excitation-contraction (E-C) coupling. Its activation
initiates three sequential events: charge movement (Qr),
calcium release, and calcium current (ICa,L). This relationship suggests that changes in Qr might affect
release and ICa,L. Here we studied the effect of
gabapentin (GBP) on the three events generated by DHPRs in skeletal
myotubes in culture. GBP specifically binds to the
2/
1 subunit of the brain and
skeletal muscle DHPR. Myotubes were stimulated with a protocol that
included a depolarizing prepulse to inactivate voltage-dependent
proteins other than DHPRs. Gabapentin (50 µM) significantly increased
Qr while decreasing the rate of rise of calcium transients.
Gabapentin also reduced the maximum amplitude of the
ICa,L (as we previously reported) without
modifying the kinetics of activation. Exposure of GBP-treated myotubes
to 10 µM nifedipine prevented the increase of Qr promoted
by this drug, indicating that the extra charge recorded originated from
DHPRs. Our data suggest that GBP dissociates the functions of the DHPR
from the initial voltage-sensing step and implicates a role for the
2/
1 subunit in E-C coupling.
dihydropyridine receptor; excitation-contraction coupling; calcium channels; calcium transients; skeletal muscle
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INTRODUCTION |
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EXCITATION-CONTRACTION
(E-C) coupling in skeletal muscle depends on the activation of
dihydropyridine receptors (DHPRs). The skeletal muscle DHPR is composed
of the pore-forming, voltage-sensing 11.1-subunit and
the auxiliary subunits
2/
1,
1, and
1 (9, 40). Upon
membrane depolarization, DHPRs undergo conformational changes that give
rise to three sequential events: charge movement (Q), calcium release,
and calcium current (ICa,L) (16).
Charge movement is the electrical manifestation of the movement of the voltage sensor in response to changes in membrane potential. Further conformational changes in the
11.1 protein lead to
activation of the sarcoplasmic reticulum (SR), calcium release channel,
or ryanodine receptor type 1 (RyR1) (16, 36). The portion
of the
11.1 protein involved in controlling calcium
release from the SR is the cytoplasmic loop connecting repeats II and
III (10, 23, 36). The last event,
ICa,L, occurs when the
11.1 has suffered additional changes that allow channel opening and calcium influx.
The sequential relationship of the events resulting from DHPR
activation would predict that any maneuvers that alter the
conformational changes in 11.1 would have a similar
effect on Q, calcium release, and ICa,L. In
support of this hypothesis, many experiments have demonstrated that
inhibition of the DHPR voltage sensor (e.g., maintained
depolarizations, DHPR antagonists, or changes in calcium levels)
reduces Q, calcium release, and ICa,L with a
similar time course and magnitude (5, 12, 13, 15, 21, 30).
However, other studies have revealed alternative effects on E-C
coupling. For example, the voltage dependence of charge movement and
calcium release (or contraction properties) is shifted in the
hyperpolarizing direction without changes in the voltage dependence of
ICa,L in the presence of perchlorate (6,
11, 19) or the R615C mutation in the RyR1 (7). In
addition, the DHP nifedipine is also able to induce calcium release
(39) and modify contractile activity (22)
while blocking ICa,L. The differential effects
of perchlorate and nifedipine on the events generated by DHPRs indicate
that E-C coupling can be modulated at different steps, leading to the generation of charge movement, calcium release, and
ICa,L.
We have recently reported that the analgesic and antiepileptic drug
gabapentin (GBP) causes a modest reduction of
ICa,L in mouse skeletal myotubes
(2). In the present paper we have extended those studies
and examined the effect of GBP on charge movement and calcium release
in mouse myotubes. Interestingly, GBP binds to
2/
1-subunits from brain and
skeletal muscle with similar kinetics and high affinity
(kd = 38 nM in brain and 29 nM in skeletal muscle) (17, 34). Gee et al. (17) have
also shown that, from 14 different tissues examined in the rat, the
highest level of GBP-binding sites occurs in skeletal muscle.
Therefore, this agent is unique because it binds to a subunit of the
DHPR complex other than the
11.1, which is considered to
be the voltage sensor. Our present studies demonstrate that GBP
increases charge movement and decreases the rate of calcium release,
suggesting that the ability of the DHPR to trigger calcium release and
to function as a calcium channel is impaired by this agent.
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MATERIALS AND METHODS |
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The experiments were approved by the Animal Care and Use Committee of the University of Illinois at Chicago and were conducted according to the Guide for the Care and Use of Laboratory Animals (National Academy of Sciences, Washington, DC, 1996).
Skeletal myotube cultures. Primary cultures of skeletal muscle tissues were prepared as previously described (14). Skeletal muscle of newborn mice was removed and finely minced. The small pieces of muscle were incubated at 37°C for 30-45 min in Ca2+, Mg2+-free rodent Ringer (in mM: 155 NaCl, 5 KCl, 11 glucose, and 10 HEPES, pH 7.4) containing collagenase type IA (1 mg/ml) (Sigma Chemical, St. Louis, MO). Dissociated muscle was triturated with a Pasteur pipette in plating medium [vol/vol, 80% Dulbecco's modified Eagle's medium (DMEM) with 4.5 g/l glucose, 10% horse serum, and 10% calf serum]. Large debris was removed from the solution by filtration and centrifugation, and a suspension of myocytes was obtained. Cultures were maintained in a 37°C incubator with a gas mixture of 95% air and 5% CO2. Skeletal myotubes were studied at 7-10 days after initial plating, and all experiments were preformed at room temperature.
Charge movement measurements.
The whole cell configuration of the patch-clamp technique
(20) was used for measurement of intramembrane charge
movement, calcium transients, and ICa,L in
skeletal myotubes. Data acquisition was synchronized with pulse
generation by a personal computer-controlled 12-bit
analog-to-digital/digital-to-analog Digidata 1200A converter. Linear
components of the membrane were digitally subtracted by appropriate
scaling and subtracting negative control currents that do not activate
ionic conductances. Membrane capacitance was measured by integrating
the area under the capacity transient before series resistance
compensation and was used to normalize the charge moved and
ICa,L measurements obtained from different myotubes. Data acquisition and processing were performed with pCLAMP
7.0 software (Axon Instruments). Recording electrodes were pulled from
borosilicate glass and had resistances between 1.6 and 2.0 M when
filled with a solution containing (in mM) 140 Cs-aspartate, 5 Mg2Cl, 10 Cs-EGTA, and 10 HEPES, pH 7.4 adjusted with CsOH.
The extracellular solution used to record charge movement contained (in
mM) 145 TEACl, 2 CaCl2, 10 HEPES, 8 MgCl2, 0.5 CdCl2, 0.1 LaCl3, and 0.003 TTX, pH 7.4 adjusted with CsOH. For calcium transients and
ICa,L recording, the extracellular solution
contained 145 TEACl, 10 CaCl2, 10 HEPES, and 0.003 TTX, pH
7.4 adjusted with CsOH. Gating currents were elicited with 15-ms test
pulses delivered from a holding potential of
80 mV in 10-mV
increments from
40 to +60 mV. To isolate gating currents due to DHPRs
and minimize contributions of gating currents from T-type, potassium, and sodium channels, we used a prepulse protocol, as described in Adams
et al. (1). In this protocol, a 1-s depolarizing pulse to
30 mV is followed by a 25-ms repolarization to
50 mV and test
pulses of varying amplitude. This voltage-dependent mechanism was used
to partially immobilize the movement of positively charged amino acids
or voltage sensors. The portion of charge movement resistant to the
effect of a prepulse, herein referred to as Qr, represents
the gating current of the DHPR, whereas the component of total charge
(Qt) that is sensitive to the prepulse (Qs)
presumably represents gating currents from T-type, potassium, and
sodium channels (1). To determine the nifedipine-sensitive
component of the gating current, paired recordings were performed
in the absence and presence of 10 µM nifedipine (Sigma
Chemical). GBP was kindly provided by Parke-Davis Research
Laboratories (Warner-Lambert, Ann Arbor, MI). Skeletal muscle cells
were incubated with 50 µM GBP for 1 h before examination, and it
was maintained in the external recording solution.
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Calcium transient measurements.
Changes in intracellular calcium concentration were measured with the
cell-impermeant fluorescent dye K5Fluo-3 (200 µM;
Molecular Probes), as previously described (14).
Individual cells were directly loaded through the patch pipette with
Fluo-3 added to the internal solution (contents listed above).
Fluorescence emission was collected with a photomultiplier tube mounted
to the side port of a Nikon Diaphot 300 inverted microscope. The set of
filters used for calcium measurements was as follows: excitation
centered at 470 nm (±20 nm); dichroic long-pass mirror centered at 510 nm; and long-pass emission filter centered at 520 nm. The background fluorescence was measured for each myotube in the cell-attached mode
before opening of the patch pipette. Measurement of changes in
intracellular calcium concentration was expressed as F/F
(14), where
F denotes an increase in fluorescence from
baseline values and F is baseline fluorescence measured before
depolarization. Transients were recorded simultaneously with
ICa,L and were elicited with 100-ms test pulses
using the prepulse protocol.
Curve fitting and statistical analysis.
For each cell, the voltage dependence of charge movement, calcium
transient (F/F), and calcium conductance (G) was fitted to a Boltzmann distribution
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(1) |
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RESULTS |
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Effect of depolarizing prepulse on charge movement, calcium
transients, and ICa,L.
We used a prepulse protocol to isolate the events resulting from
activation of DHPRs. Figure 2A
shows records of charge movement obtained from skeletal myotubes in the
absence and presence of a prepulse at different test potentials. The
voltage dependence of the total charge movement and the charge
resistant to a depolarizing prepulse are shown in the graph in Fig.
2A. The difference between the total and resistant charges
represents the charge that can be inactivated by the prepulse and
corresponds to voltage-sensitive channels other than the DHPR
(1). The average amount of Qt was 9.5 ± 0.9 nC/µF, and the average of Qr was 5.2 ± 0.6 nC/µF (n = 27). These values of charge movement are
in close agreement with values previously reported (1, 16,
28). The curve corresponding to Qt has a more
negative V1/2 (16.8 ± 1.1 mV) than the
Qr curve (
6.2 ± 1.7 mV) because it contains charge from voltage-dependent proteins that activate at lower membrane potentials than the DHPR. The average value of k was
10.21 ± 0.6 and 12.36 ± 0.5 mV in the absence and presence
of the prepulse, respectively.
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Increase of immobilization-resistant charge movement by GBP.
When skeletal myotubes were exposed to GBP, we found a large increase
in Qr compared with untreated myotubes. Figure
3A shows representative
records of Qr obtained in the absence and presence of GBP.
The values of Qr were averaged at each membrane potential and used to construct the voltage dependence shown in Fig.
3B. The increase in Qr in the presence of GBP
was observed for membrane potentials from 30 to 60 mV. The average
maximum Qr in GBP-treated and control myotubes was 8.9 ± 0.9 (n = 23) and 5.1 ± 0.6 nC/µF (n = 31), respectively (P < 0.05). The
average values of the other parameters describing the voltage
dependence in GBP-treated myotubes were V1/2 =
8.0 ± 3.8 mV and k = 13.2 ± 1.3 mV
(n = 23), whereas the corresponding values for control
myotubes were V1/2 =
6.2 ± 1.9 mV and
k = 12.36 ± 0.5 mV (n = 31). The
difference in the parameters of voltage dependence between the two
conditions was not significant (P > 0.05). The graph
in Fig. 3B shows normalized Qr to the maximum
value for GBP-treated and control myotubes, where the similarity of the
voltage dependence can be better appreciated. Because Qr is
thought to represent the movement of the DHPR voltage sensor in the
membrane, the increase in Qr indicates that GBP facilitates
the movement of the receptor, yet it does not modify the voltage
dependence.
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Effect of GBP on calcium transients.
Figure 4 shows typical calcium transients
elicited from a control myotube (Fig. 4A) and a GBP-treated
myotube (Fig. 4B) at 30, 0, and 50 mV. Calcium transients
were also elicited with the prepulse protocol. The maximum amplitude of
the calcium transients, measured at the end of the pulse, in
GBP-treated myotubes (
F/F = 1.15 ± 0.19;
n = 14) was similar to the amplitude of the transients recorded from control myotubes (1.25 ± 0.14; n = 20) (P > 0.05). The average values of
V1/2 and k for GBP-treated myotubes were
0.56 ± 1.7 and 6.23 ± 0.4 mV (n = 14), respectively, and for control myotubes they were
4.78 ± 1.0 and 4.56 ± 0.4 mV (n = 20). Figure 4,
C and D, shows the voltage dependence of calcium transients in absolute and normalized values, respectively, to demonstrate that the parameters of activation were not modified (P > 0.05).
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Effect of GBP on ICa,L and conductance.
GBP caused a small but significant reduction of
ICa,L at membrane potentials between 20 and 40 mV compared with control cells, as shown in Fig.
5. Figure 5A shows typical
records of ICa,L in untreated and GBP-treated
myotubes at different membrane potentials. The conductance of the
calcium channel was calculated by fitting the
ICa,L data to a Boltzmann equation:
I(V) = GmaxL · (V Vr)/[1 + exp(VL
V)/kL], where
I(V) is the maximum ICa,L
at a given test potential, GmaxL is
the maximum L-type channel conductance, Vr is
the reversal potential for calcium, V is the test potential, VL is the half-maximal activation potential for
the L-type channel, and kL is the
slope factor. Comparison of the conductance-voltage (G-V)
relationships is shown in Fig. 5B. As demonstrated,
conductance values were significantly decreased in GBP-treated cells at
positive membrane potentials compared with control cells. However, the reduction of calcium conductance was not accompanied by a significant change of the activation parameters, as shown by the graph in Fig.
5C. The average values of the activation parameters were as
follows: in control myotubes, VL = 9.4 ± 1.0 mV, kL = 4.3 ± 0.2 mV, and
Vr = 79.2 ± 1.4 mV (n = 41); in GBP-treated myotubes, VL = 10.5 ± 1.5 mV, kL = 4.6 ± 0.5 mV, and Vr = 80.0 ± 1.3 mV (n = 24) (P > 0.05).
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Nifedipine blocks enhancement of Qr by GBP.
Because GBP increased Qr while decreasing both the rate of
calcium release and ICa,L, it could be argued
that a voltage-sensitive membrane protein other than the DHPR produced
the additional charge movement recorded in GBP-treated cells. We tested
this hypothesis by using nifedipine, a specific DHPR blocker.
Recordings of Qr in the absence and the presence of 10 µM
nifedipine were obtained from control and GBP-treated myotubes, as
shown in Fig. 6A. On average,
nifedipine decreased the maximum Qr to a larger extent in
GBP-treated myotubes (60 ± 3%, n = 16) compared
with the reduction in untreated myotubes (25 ± 3.5%;
n = 25). Thus the application of nifedipine equalized
the amount of maximum Qr in control (3.9 ± 0.3 nC/µF; n = 25) and GBP-treated myotubes (3.6 ± 0.3 nC/µF; n = 16), as shown in Fig. 6B.
The percent reduction in Qr by nifedipine in control
myotubes is consistent with other studies. For example, Strube et al.
(33) showed a 33% reduction in charge movement (Qt) from developing skeletal muscle. The decrease of
Qr in myotubes treated with GBP and nifedipine thus
indicates that the extra charge recorded from GBP-treated myotubes is
indeed generated by the DHPR.
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GBP decreases the effectiveness of the DHPR in E-C coupling.
To have an objective measure of the dissociation of Qr and
calcium release and ICa,L caused by GBP, we
compared the rate of release and conductance as a function of
Qr. These data are shown in Fig.
7 for control and GBP-treated myotubes.
As shown, GBP shifted the curves to the right, which indicates that
more immobilization-resistant charge is needed to attain similar levels
of rate of release or conductance. The amount of Qr
required for the same value of rate of release or conductance was
roughly two times greater in the presence of GBP than the amount of
Qr required in control myotubes. Moreover, in GBP-treated
myotubes, the maximum rate of release did not reach control levels.
Thus this analysis indicates that GBP decreased the effectiveness of
the DHPR as a voltage sensor necessary for calcium release and as a
calcium channel.
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DISCUSSION |
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We report a novel regulatory effect of GBP on the E-C coupling mechanism in skeletal muscle. The effect is characterized by dissociation of Qr from calcium release and ICa,L. Two lines of evidence indicate that GBP exerted its effects by acting on the DHPR. First, GBP did not modify the midpoint potential of activation (V1/2) or the slope (k) of the curves of any of the events produced by activation of the DHPR. Second, the increase of Qr caused by GBP was antagonized by nifedipine, such that the amount of Qr remaining in the presence of GBP and nifedipine was similar to that in myotubes treated with nifedipine alone.
Based on the voltage dependence and time course of activation of
Qr, calcium release, and ICa,L, a
sequential scheme of the conformational changes in the DHPR has been
proposed (16). This model would predict that any agent
that modifies Qr would have a similar effect on calcium
release and ICa,L. However, other studies have
shown that perchlorate and nifedipine may also have differential
effects on the events generated by the DHPR (6, 22). The
target proteins involved in the actions of perchlorate are thought to
be the 11.1-subunit of the DHPR and/or the RyR1 (24), whereas nifedipine acts on the
11.1-subunit (39), where its binding site
is localized (26). In this respect, the effect of GBP on
E-C coupling is unique because the
2/
-subunit
has been identified as the GBP receptor (17), and its
binding site has been localized on the extracellular portion of the
2/
1-subunit of the DHPR
(4, 38).
The remote possibility exists that the effect of GBP on E-C coupling is
unrelated to its interaction with the
2/
1-subunit and that GBP may also
bind to the
11.1 subunit (in addition to the
2/
1-subunit) because of the
concentration of the drug used in these experiments (50 µM). However,
calculation of the slope of the curve fitted to the data in Fig. 1
resulted in a value of 1.05, indicating that GBP bound to a single
population of sites in myotubes. This result agrees with previous
studies by Gee et al. (17) using rat muscle membranes,
where GBP also bound to one population of sites. Furthermore,
radioligand binding and immunoblotting studies of fractionated L-type
calcium channels isolated from skeletal muscle determined that GBP
bound to the
2/
1-subunit even at
high concentrations. Thus it is conceivable that the effects of GBP on
E-C coupling we have elucidated are mediated by the
2/
1-subunit.
Our results suggest that GBP binding to the
2/
1-subunit would affect the
conformational changes experienced by the
11.1-subunit during DHPR activation. Only a few amino acids of the
2/
1 protein are found on the
cytoplasmic side of the membrane, the remainder being located either
within the membrane or on the extracellular side (18). For
this reason, it is attractive to hypothesize that the
GBP-
2/
1-subunit complex acts on
the transmembrane repeats and perhaps the outer portion of the
11.1-subunit. Initially the interaction between the
GBP-
2/
1-subunit complex and
11.1 would favor the movement of the repeats resulting
in a larger Qr. Subsequently, the complex would prevent the
fast and complete change of repeats II and III (and the II-III
cytoplasmic loop). This would result in slower activation of the RyR1
and an attenuated rate of calcium release. Finally, the decrease in
ICa,L amplitude may be explained by a blocking
effect of the GBP-
2/
1-subunit complex. The block may occur on the extracellular side of the calcium
channel because it has been shown that the external portion of the
2/
1-subunit is required for
current stimulation (18). Although repeat I in the
11.1-subunit is thought to set the activation rate of
the ICa,L (35), we do not believe the complex
is modifying the movement of repeat I because the time constants of
activation of the current were similar in untreated and GBP-treated myotubes.
Whether the GBP-binding properties to the
2/
1-subunit in skeletal myotubes
are independent of the presence or absence of a prepulse cannot be
determined from our experiments. As Adams et al. (1) have
previously shown and we mentioned earlier, we need to use a prepulse to
record the activity of the DHPR separate from other voltage-dependent
proteins in skeletal myotubes. However, we have previously shown that
the effect of GBP on neuronal calcium channels is noticed only after
the application of a prepulse (2).
In recent studies using expression systems, other investigators have
shown that charge movement arising from the cardiac
11.2-subunit is modulated by coexpression of the
2/
-subunit (3, 29, 31). Although
the experimental systems between those reports and this manuscript are
different and calcium transients were not studied earlier, they agree
with our finding that the
2/
1-subunit may control the gating
of the
11.1-peptide. However, we further consider that
the in situ function of the
2/
1-subunit may be to effectively
couple gating current with calcium release and channel opening.
Taken together the data presented in this work suggest the presence of
several closed states before the DHPR is fully activated and that these
states can be affected by GBP. Our results are also the first to
provide information about the involvement of the
2/
1-subunit in skeletal muscle E-C coupling.
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ACKNOWLEDGEMENTS |
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We thank Dr. Tord D. Alden for help with the statistical analysis and Tanvi M. Shah for laboratory assistance.
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FOOTNOTES |
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This work was supported by National Science Foundation Grant IBN-9733570 (to J. García). K. Alden was partially supported by National Institute of Diabetes and Digestive and Kidney Diseases Training Grant T32 DK-07739-02.
Address for reprint requests and other correspondence: J. García, Dept. of Physiology and Biophysics, Univ. of Illinois at Chicago College of Medicine, 900 S. Ashland Ave., M/C 902, Chicago, IL 60607 (E-mail: garmar{at}uic.edu).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
May 15, 2002;10.1152/ajpcell.00004.2002
Received 4 January 2002; accepted in final form 14 May 2002.
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REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Adams, BA,
Tanabe T,
Mikami A,
Numa S,
and
Beam KG.
Intramembrane charge movement restored in dysgenic skeletal muscle by injection of dihydropyridine receptor cDNAs.
Nature
346:
569-572,
1990[ISI][Medline].
2.
Alden, KJ,
and
García J.
Differential effect of gabapentin on neuronal and muscle calcium currents.
J Pharmacol Exp Ther
297:
727-735,
2001
3.
Bangalore, R,
Mehrke K,
Gingrich K,
Hofmann F,
and
Kass RS.
Influence of L-type Ca channel 2
-subunit on ionic and gating current in transiently transfected HEK 293 cells.
Am J Physiol Heart Circ Physiol
270:
H1521-H1528,
1996
4.
Brown, JP,
and
Gee NS.
Cloning and deletion mutagenesis of the 2
calcium channel subunit from porcine cerebral cortex. Expression of a soluble form of the protein that retains [3H]gabapentin binding activity.
J Biol Chem
273:
25458-25465,
1998
5.
Chandler, WK,
Rakowski RF,
and
Schneider MF.
Effects of glycerol treatment and maintained depolarization on charge movement in skeletal muscle.
J Physiol
254:
285-316,
1976[Abstract].
6.
Csernoch, L,
Kovacs L,
and
Szucs G.
Perchlorate and the relationship between charge movement and contractile activation in frog skeletal muscle fibres.
J Physiol
390:
213-227,
1987[Abstract].
7.
Dietze, B,
Henke J,
Eichinger HM,
Lehmann-Horn F,
and
Melzer W.
Malignant hyperthermia mutation Arg615Cys in the porcine ryanodine receptor alters voltage dependence of Ca2+ release.
J Physiol
526:
507-514,
2000
8.
Dirksen, RT,
and
Beam KG.
Single calcium channel behavior in native skeletal muscle.
J Gen Physiol
105:
227-247,
1995[Abstract].
9.
Eberst, R,
Dai S,
Klugbauer N,
and
Hofmann F.
Identification and functional characterization of a calcium channel gamma subunit.
Pflügers Arch
433:
633-637,
1997[ISI][Medline].
10.
El-Hayek, R,
Antoniu B,
Wang J,
Hamilton SL,
and
Ikemoto N.
Identification of calcium release-triggering and blocking regions of the II-III loop of the skeletal muscle dihydropyridine receptor.
J Biol Chem
270:
22116-22118,
1995
11.
Feldmeyer, D,
and
Lüttgau HC.
The effect of perchlorate on Ca currents and mechanical force in skeletal muscle fibres (Abstract).
Pflügers Arch
411:
R190,
1988.
12.
Feldmeyer, D,
Melzer W,
and
Pohl B.
Effects of gallopamil on calcium release and intramembrane charge movements in frog skeletal muscle fibres.
J Physiol
421:
343-362,
1990[Abstract].
13.
García, J,
Avila-Sakar AJ,
and
Stefani E.
Differential effects of ryanodine and tetracaine on charge movement and calcium transients in frog skeletal muscle.
J Physiol
440:
403-417,
1991[Abstract].
14.
García, J,
and
Beam KG.
Measurement of calcium transients and slow calcium current in myotubes.
J Gen Physiol
103:
107-123,
1994[Abstract].
15.
García, J,
Pizarro G,
Rios E,
and
Stefani E.
Effect of the calcium buffer EGTA on the "hump" component of charge movement in skeletal muscle.
J Gen Physiol
97:
885-896,
1991[Abstract].
16.
García, J,
Tanabe T,
and
Beam KG.
Relationship of calcium transients to calcium currents and charge movements in myotubes expressing skeletal and cardiac dihydropyridine receptors.
J Gen Physiol
103:
125-147,
1994[Abstract].
17.
Gee, NS,
Brown JP,
Dissanayake VU,
Offord J,
Thurlow R,
and
Woodruff GN.
The novel anticonvulsant drug, gabapentin (Neurontin), binds to the 2
subunit of a calcium channel.
J Biol Chem
271:
5768-5776,
1996
18.
Gurnett, CA,
De Waard M,
and
Campbell KP.
Dual function of the voltage-dependent Ca2+ channel 2
subunit in current stimulation and subunit interaction.
Neuron
16:
431-440,
1996[ISI][Medline].
19.
Gyorke, S,
and
Palade P.
Effects of perchlorate on excitation-contraction coupling in frog and crayfish skeletal muscle.
J Physiol
456:
443-451,
1992[Abstract].
20.
Hamill, OP,
Marty A,
Neher E,
Sakmann B,
and
Sigworth FJ.
Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches.
Pflügers Arch
391:
85-100,
1981[ISI][Medline].
21.
Huang, CL.
Charge movements in intact amphibian skeletal muscle fibres in the presence of cardiac glycosides.
J Physiol
532:
509-523,
2001
22.
Kitamura, N,
Ohta T,
Ito S,
and
Nakazato Y.
Effects of nifedipine and Bay K 8644 on contractile activities in single skeletal muscle fibers of the frog.
Eur J Pharmacol
256:
169-176,
1994[ISI][Medline].
23.
Leong, P,
and
MacLennan DH.
A 37-amino acid sequence in the skeletal muscle ryanodine receptor interacts with the cytoplasmic loop between domains II and III in the skeletal muscle dihydropyridine receptor.
J Biol Chem
273:
7791-7794,
1998
24.
Ma, J,
Anderson K,
Shirokov R,
Levis R,
Gonzalez A,
Karhanek M,
Hosey MM,
Meissner G,
and
Rios E.
Effects of perchlorate on the molecules of excitation-contraction coupling of skeletal and cardiac muscle.
J Gen Physiol
102:
423-448,
1993[Abstract].
25.
Melzer, W,
Rios E,
and
Schneider MF.
Time course of calcium release and removal in skeletal muscle fibers.
Biophys J
45:
637-641,
1984[Abstract].
26.
Mitterdorfer, J,
Wang Z,
Sinnegger MJ,
Hering S,
Striessnig J,
Grabner M,
and
Glossmann H.
Two amino acid residues in the IIIS5 segment of L-type calcium channels differentially contribute to 1,4-dihydropyridine sensitivity.
J Biol Chem
271:
30330-30335,
1996
27.
Nabhani, T,
Zhu X,
Simeoni I,
Sorrentino V,
Valdivia HH,
and
García J.
Imperatoxin A enhances Ca2+ release in developing skeletal muscle containing ryanodine receptor type 3.
Biophys J
82:
1319-1328,
2002
28.
Nakai, J,
Dirksen RT,
Nguyen HT,
Pessah IN,
Beam KG,
and
Allen PD.
Enhanced dihydropyridine receptor channel activity in the presence of ryanodine receptor.
Nature
380:
72-75,
1996[ISI][Medline].
29.
Platano, D,
Qin N,
Noceti F,
Birnbaumer L,
Stefani E,
and
Olcese R.
Expression of the 2
subunit interferes with prepulse facilitation in cardiac L-type calcium channels.
Biophys J
78:
2959-2972,
2000
30.
Rios, E,
and
Brum G.
Involvement of dihydropyridine receptors in excitation-contraction coupling in skeletal muscle.
Nature
325:
717-720,
1987[ISI][Medline].
31.
Shirokov, R,
Ferreira G,
Yi J,
and
Ríos E.
Inactivation of gating currents of L-type calcium channels. Specific role of the 2
subunit.
J Gen Physiol
111:
807-823,
1998
32.
Stefani, A,
Spadoni F,
and
Bernardi G.
Gabapentin inhibits calcium currents in isolated rat brain neurons.
Neuropharmacology
37:
83-91,
1998[ISI][Medline].
33.
Strube, C,
Bournaud R,
Inoue I,
and
Shimahara T.
Intramembrane charge movement in developing skeletal muscle cells from fetal mice.
Pflügers Arch
421:
572-577,
1992[ISI][Medline].
34.
Suman-Chauhan, N,
Webdale L,
Hill DR,
and
Woodruff GN.
Characterisation of [3H]gabapentin binding to a novel site in rat brain: homogenate binding studies.
Eur J Pharmacol
244:
293-301,
1993[Medline].
35.
Tanabe, T,
Adams BA,
Numa S,
and
Beam KG.
Repeat I of the dihydropyridine receptor is critical in determining calcium channel activation kinetics.
Nature
352:
800-803,
1991[ISI][Medline].
36.
Tanabe, T,
Beam KG,
Adams BA,
Niidome T,
and
Numa S.
Regions of the skeletal muscle dihydropyridine receptor critical for excitation-contraction coupling.
Nature
346:
567-569,
1990[ISI][Medline].
37.
Wamil, AW,
and
McLean MJ.
Limitation by gabapentin of high frequency action potential firing by mouse central neurons in cell culture.
Epilepsy Res
17:
1-11,
1994[ISI][Medline].
38.
Wang, M,
Offord J,
Oxender DL,
and
Su TZ.
Structural requirement of the calcium-channel subunit 2
for gabapentin binding.
Biochem J
342:
313-320,
1999[ISI][Medline].
39.
Weigl, LG,
Hohenegger M,
and
Kress HG.
Dihydropyridine-induced Ca2+ release from ryanodine-sensitive Ca2+ pools in human skeletal muscle cells.
J Physiol
525:
461-469,
2000
40.
Witcher, DR,
De Waard M,
Sakamoto J,
Franzini-Armstrong C,
Pragnell M,
Kahl SD,
and
Campbell KP.
Subunit identification and reconstitution of the N-type Ca2+ channel complex purified from brain.
Science
261:
486-489,
1993[ISI][Medline].
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