1Membrane Transport Group, Department of Chemistry, The Faculties, The Australian National University, Canberra, Australian Capital Territory 0200; 2Department of Pathology, The University of Melbourne, Victoria 3010; and 3The Mental Health Research Institute, Parkville, Victoria 3052, Australia
Submitted 14 April 2003 ; accepted in final form 21 May 2003
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ABSTRACT |
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neurodegenerative diseases; transitional metals; ion channel pathologies; membrane injuries; calcium homeostasis
In addition to the A being linked to AD, a role for transition metals
has also been recognized. Cu2+ and Zn2+ have been
implicated in AD (11,
12,
42), Parkinson's disease
(54), prion protein (PrP)
(26), and immunoglobulin light
chain amyloidosis (17). The
mechanisms underlying the interaction between A
and these metals may
mediate their role in neurotoxicity. There is also evidence to show that
A
, and also PrP, binds Cu2+
(5,
6) to a site resembling that of
superoxide dismutase (16) and
metalloenzyme-like activity
(44). The A
-formed
channels are redox sensitive and modulated by Zn2+
(3,
4,
35). In this study we have
examined the Cu2+ dependency of A
(1-42)-formed channels.
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MATERIALS AND METHODS |
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Lipid bilayer technique. Bilayers were formed across a 150-µm
hole in the wall of a 1-ml Delrin T cup using a mixture of
palmitoyl-oleoyl-phosphatidylethanolamine,
palmitoyl-oleoyl-phosphatidylserine, and palmitoyl-oleoyl-phosphatidylcholine
(5:3:2, by volume) and palmitoyl-oleoyl-phosphatidylethanolamine,
palmitoyl-oleoyl-phosphatidylserine (7:3 by volume)
(36,
40), obtained in chloroform
from Avanti Polar Lipids (Alabaster, AL). The lipid mixture was dried under a
stream of N2 and redissolved in n-decane at a final
concentration of 50 mg/ml. A(1-42) was synthesized by the W. Keck
Laboratory (Yale University, New Haven, CT). A
stock solutions were
prepared in experimental cis solutions and kept at -80°C till
use. A
(1-42) was then incorporated into the negatively charged lipid
bilayer by addition to the cis chamber of A
(1-42) liposomes
(2) or aliquots of A
stock solution at a final peptide concentration of 0.1-1 µg/ml. The side of
the bilayer to which the peptide or liposomes were added is defined as
cis, and the other side as trans. Ion channels were also
recorded from a peptide-lipid mixture of 1:50. Unless stated otherwise, the
initial experimental solution for incorporating synthetic A
(1-42) into
the bilayers contained KCl (250 mM cis/50 mM trans). Other
reagents were obtained from Sigma unless otherwise noted. The experiments were
conducted at 20-25°C.
Preparation of liposomes. In some experiments, liposomes of
A(1-42) were used. The method for the preparation of these liposomes was
described by Arispe et al. (3).
A 20-µl aliquot of palmitoyl-oleoyl-phosphatidylserine dissolved in
chloroform (10 mg/ml) was placed in a glass tube. After evaporation of the
chloroform (by blowing filtered N2 gas), a 30-µl aliquot of 1 M
potassium aspartate (pH adjusted to 7.2) was added and the resulting mixture
was sonicated for 5 min. Next, a 20 µl (2 mg/ml) stock solution of the
A
(1-42) in water was added, and the adduct was sonicated for 2 min.
Ion channel recording. The pCLAMP6 program (Axon Instruments) was used for voltage command and acquisition of ionic current families with an Axopatch 200 amplifier (Axon Instruments). The current was monitored with an oscilloscope, and the data were stored on a computer. The cis and trans chambers were connected to the amplifier head stage by Ag-AgCl electrodes in agar salt bridges containing the solutions present in each chamber. Voltages and currents are expressed relative to the trans chamber. An outward current is defined as a cation moving from the cis chamber to the trans chamber or an anion moving from the trans chamber to the cis chamber. Data were filtered at 1 kHz (4-pole Bessel, -3 dB) and digitized via a TL-1 DMA interface (Axon Instruments) at 2 kHz.
Data analysis. Modifications in the bilayer thickness, mediated
via lipid solvents, e.g., n-decane, contribute to changes in channel
gating kinetics of ion channels
(31,
36) and particularly those
formed with short peptides, e.g., the 15-amino acid gramicidin-formed channel
(43). Therefore, standardizing
the specific membrane capacitance (Cb) and its time
independence is important in comparative and detailed investigations of ion
channel characteristics. Kinetic analysis for the A(1-42)-formed
channels was conducted only for optimal bilayers having a
Cb of >0.42 µF/cm2 and containing a
single active channel. The criteria for defining ion currents as belonging to
a "single channel" have been described elsewhere
(14a). Single-channel activity
was analyzed for overall characteristics using the program CHANNEL 2
(developed by Gage PW and Smith M; see Ref.
36). The following kinetic
parameters of single-channel activity (32- to 128-s-long records) were
determined: mean open time, To (i.e., the average of the
open times of all intervals where the current exceeded the baseline noise for
0.5 ms); frequency of opening to all conductance levels,
Fo; and open probability, Po (i.e.,
the sum of all open times as a fraction of the total time). CHANNEL 2 also
allows online analysis of the entire current record for computation of the
maximal current (I) and mean current (I').
I' is defined as the integral of the current passing through
the channel divided by the total time. The integral current is determined by
computation of the area between a line set on the noise of the closed state
and channel opening to various levels. The threshold level for the detection
of single-channel events was set at 50% of the maximum current
(45). The maximal current is
the current amplitude of a fully open channel. The maximal current was
obtained by measuring the distance (in pA) between two lines, one set on the
noise of the closed level where the current amplitude is 0 pA and the other
set on the noise of the majority of distinct events that were in the open
state. The maximal current was also obtained by measuring the distance (in pA)
between the peak at 0 pA (representing the closed state) and the extreme peak
on the right (representing the open state) in the all-point histogram
generated using CHANNEL 2 (see Ref.
36). Both methods were used,
and the results were generally in agreement. The reversal potential
Erev was corrected for ionic mobility and liquid junction
potential (8). SigmaPlot
(Jandel Scientific Software) was used to plot and calculate curve fit of the
data. Data are reported as means ± SE, and the difference in means was
analyzed by using Student's t-test. Data were considered
statistically significant when P values were
0.05.
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RESULTS |
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Figure 2, A-F,
shows groups of four representative current traces recorded from the same
bilayer containing A(1-42) channels exposed to different
[Cu2+]cis between 0 and 250 µM and clamped
at +140 mV. Several seconds after the addition of 50 µM Cu2+,
changes in channel activity were observed
(Fig. 2B). The most
apparent effects were the lengthening of the long durations of channel
inactivity, i.e., intrabursts, and changes in the activity of the channel
within the burst. The channel activity was modified further after subsequent
additions to 100, 150, 200, and 250 µM
[Cu2+]cis
(Fig. 2, C-F). These
findings are in agreement with Cu2+-induced inhibition of the
deamidated-type of PrP(106-126)-formed channels
(34), where Cu2+
induced long-duration channel closures at positive voltages. The effects of
250 µM [Cu2+]cis on A
(1-42) channels
could not be reversed with the addition of 112 µM CQ, which selectively
binds Cu2+, to the cis solution
(Fig. 2G). The channel
activity recovered partially after wash with control cis solution
containing 250 mM KCl (Fig.
2H). Furthermore, the addition of 128 µM
[CQ]cis produced only a little additional recovery to the
channel activity (Fig.
2I). Similarly, 384 µM [CQ]cis did
not prevent channel inhibition induced with 100 µM
[Cu2+]cis (data not shown).
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Effects on A(1-42) channel conductance. Data
analysis with CHANNEL 2 (36)
revealed that the Cu2+-induced decrease in I and
I' was exponential (Fig.
3). Cu2+ reduced the channel current amplitude by
38.34%; the current amplitudes were 8.9 ± 0.4 and 6.3 ± 0.6 pA
in the presence and absence of 100 µM Cu2+ at a membrane
potential (Vm) of +140 mV, respectively (n = 16
traces). However, current amplitude was further reduced to 5.5 ± 0.4 pA
in 200 µM Cu2+ and a Vm of +140 mV.
I' was reduced from 4.5 to 1.22 pA (27.11%) as
[Cu2+]cis increased to 200 µM. No channel
activity was observed in the presence of 250 µM
[Cu2+]cis.
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Effects on voltage dependence of A(1-42) channel
conductance. To examine the voltage dependency of
[Cu2+]cis-induced effects on the channel
activity, we used a voltage protocol to obtain single-channel currents. From
an initial holding potential of +60 mV, the bilayer potential was stepped to
voltages ranging from -160 to +140 mV, in steps of +20 mV. After the first few
milliseconds of the clamp, during which a capacitive transient current
occurred, a single-channel current was activated following each voltage step.
The current-voltage (I-V) relationships show the
Cu2+-induced changes in the voltage dependence of the maximal
current (I) (Fig.
4A), where the maximal conductance (maximal slope of
I-V) was reduced nonsignificantly from 62 pS in control to 60 pS in
100 µM [Cu2+]cis. On the other hand, the
mean current (I') was reduced significantly at positive
voltages (Fig. 4B),
being 4.5 ± 0.5 and 1.35 ± 0.2 pA in the absence and presence of
100 µM [Cu2+]cis, respectively. The
current's Erev (approximately -22 mV;
Fig. 4A) shifted
nonsignificantly (
2.5 mV), indicating that there were no changes in the
nature of the [Cu2+]cis-reduced current, which
remained a K+ current. The effects of 100 µM
[Cu2+]cis on I and I'
were reversible (Fig. 4, A and
B).
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Effects on A(1-42) channel burst kinetics. The
changes in the kinetic parameters of the channel bursts were obtained at
different [Cu2+]cis.
Figure 5, A-D, shows
the concentration dependence of the mean burst and intraburst durations and
frequencies for a channel in a bilayer that is clamped to +140 mV. The
intraburst duration and burst duration increase as
[Cu2+]cis is incremented. The burst frequency
and intraburst frequency decrease as a function of increasing
[Cu2+]cis. The
[Cu2+]cis-induced changes in these parameters
were fitted with two or three exponentials.
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Effects on A(1-42) channel kinetics within the
burst. The changes in the kinetic parameters of the channel within the
burst were also calculated at different
[Cu2+]cis.
Figure 6, A-D, shows
the concentration dependence of the Po,
Fo, To, and closed time
(Tc) for a channel in a bilayer that is clamped to +140
mV. The parameters Po, Fo, and
To decreased while Tc increased as a
function of increasing [Cu2+]cis. The values of
Po, Fo, To, and
Tc were 0.49, 106 s-1, 2.8 ms, and 3.01 ms for
control and 0.06, 91 s-1, 0.81 ms, and 14.2 ms. The
[Cu2+]cis-induced changes in these parameters
were fitted with two or three exponentials. These findings are in agreement
with those fits where drugs typically induce open channel block
(18).
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Effects on A(1-42) channel desensitization.
Figure 7 shows the
[Cu2+]cis dependence of the desensitization
parameter (burst duration x Po) of an
A
(1-42)-formed channel, in the burst mode, activated at +140 mV in KCl
(250 mM cis/50 mM trans). The
[Cu2+]cis-induced changes in the A
(1-42)
channel desensitization are biphasic, an inverted bell-shaped curve with a
minimum at 50 µM [Cu2+]cis and a bell-shaped
curve with a peak at between 100 and 150 µM
[Cu2+]cis. The third-order polynomial fit of
the data shows a decline in the channel desensitization as a function of
increasing [Cu2+]cis. The value decreases from
0.83 s-1 at 50 µM [Cu2+]cis to
0.17 s-1 at 200 µM [Cu2+]cis.
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Voltage dependence of effects of Cu2+ on
A(1-42) channel bursts kinetics. The voltage dependence of
the burst (Fig. 8A)
and intraburst durations (Fig.
8B) could be described by an inverted bell-shaped
third-order polynomial fit with a peak at approximately +80 mV. In 100 µM
[Cu2+]cis, mean burst duration was reduced and
mean intraburst duration increased at all voltages. The data show that
[Cu2+]cis affected the burst
(Fig. 8A) and
intraburst durations (Fig.
8B) in a voltage-dependent manner. The mean values of the
burst and intraburst durations in the control solution were 1.22 and 0.54 at
+80 mV and 2.63 and 1.77 at +140 mV, respectively. In 100 µM
[Cu2+]cis, these mean values for the burst and
intraburst durations were 0.60 and 5.92 s at +80 mV and 0.16 and 6.79 s at
+140 mV, respectively.
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The voltage dependence of the burst frequency (Fig. 8C) and intraburst frequency (Fig. 8D) could also be described by a bell-shaped third-order polynomial fit with a peak between +80 and 120 mV. In 100 µM [Cu2+]cis, burst frequency was reduced and intraburst frequency increased. The data show that [Cu2+]cis shifted the peak of the burst frequency (Fig. 8C) and the peak of the intraburst (Fig. 8D) shifted to more positive voltages.
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DISCUSSION |
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The effect of Cu2+ on the kinetics of A(1-42)-formed
channels is observed within 1-10 s, and the Cu2+-induced changes in
the kinetics of A
(1-42)-formed channels become evident at concentrations
as low as 50 µM (see, e.g., Figs.
2 and
6). The physiological
concentration of Cu2+ in the synapse has been reported at 250 µM
(27). However, the in vivo
Cu2+ concentration threshold necessary to induce changes in the
A
-formed ion channels that may underlie neuronal dysfunction remains to
be quantified.
A(1-42) is more lipophilic than A
(1-40), and therefore it is
expected that A
(1-42) and its intermediate aggregates should be more
stable in lipids (see Ref.
15). The findings reported in
this study on the ability of A
(1-42) to form channels together with
those reported for A
(1-40)-formed channels
(35) suggest that the two
additional residues in A
(1-42) are not essential in channel formation.
However, differences in the distribution of A
(1-40) and A
(1-42)
channel types and in their stabilities in lipid membranes cannot be ruled
out.
Kinetic of the burst and intraburst. At the single-channel level,
the effects of Cu2+ are characterized by changes in the kinetics of
the burst and the kinetics of the events within the burst (Figs.
1 and
2). In agreement with previous
findings, the kinetic parameters Po,
Fo, and To decrease while
Tc increases as [Cu2+]cis
increased (Figs. 5 and
6). The Cu2+-induced
changes in the kinetics of the bursts and the events within the burst are
described at least by two exponentials. This behavior appears to be in
agreement with that of open channel blocking drugs, which exhibit a two-phase
change in current kinetics
(18), suggesting that
Cu2+ may act on both open and closed states of the channel.
Cu2+ also affects desensitization of the A(1-42) channels
(Fig. 7). According to Auerbach
and Akk (7) and Spitzmaul et
al. (52), the value of
(
bPo)-1 (where
b is the mean cluster duration and Po is
the probability of being open within a cluster) is a direct measure of the
rate constant of desensitization. Under control conditions, these values are
as follows: Po = 0.49 and
b = 4 s, so that
(
bPo)-1 = 1.96 s-1,
whereas at 100 µM [Cu2+]cis,
Po = 0.16 and
b = 0.12 s, so that
(
bPo)-1 = 0.019 s-1.
The duration of the burst and intraburst increases, whereas the number of
bursts and intrabursts decreases at Cu2+ concentrations between 0
and 200 µM. At 250 µM [Cu2+]cis the
channel is fully inhibited and no channel activity is observed. The
lengthening of the burst and intraburst durations suggests that
Cu2+ decreases both activation and inactivation rates of the
channel. Between 50 and 200 µM [Cu2+]cis,
Po declines rapidly
(Fig. 6A) because of
the decline in To and increase in Tc
(Figs. 6C and
5D). The reversible
effects of Cu2+ at low concentrations (50-100 µM) on the channel
kinetics are consistent with its binding to a site at the mouth of the
channel.
Binding site and "fast" open channel block. Consistent
with the hydrophilic and structural properties of A(1-42), the
Cu2+-induced changes in the kinetic parameters of this channel
suggest that the Cu2+ binding site could be located at the mouth of
the channel. This is consistent with findings of Curtain et al.
(15,
16), which showed that
Cu2+ bound to the histidine residues His6,
His13, and His14 near the NH2 terminus of the
peptide, and that although the metal ions induced a channel-like structure,
the metal binding site resided above the plane of the lipid bilayer. The
findings reported here show that transition metals modulate the activity of
A
(1-42)-formed channels. This channel modulation by transition metals
could be common to other channel-forming amyloidogenic peptides. Indeed,
2-microglobulin, another amyloid channel-forming protein, formed
channels that are blocked by zinc
(22). We also have reported
that PrP(106-126) is sensitive to Cu2+ and that the metal binding
site is localized at the NH2-terminal amino group,
His111, and Met109
(26,
34). We also reported that
millimolar concentrations of Zn2+ were needed to induce a reduction
in the current amplitude of the "bursting" channel and the slow
mode of the large-conductance A
channel
(35). Similarly, Lin et al.
(38) showed that
Zn2+ inhibited A
channel activity. The findings in this study
suggest that these A
channels have higher affinity to Cu2+
than Zn2+, consistent with findings of Curtain et al.
(16). Furthermore,
Cu2+ induces a fast open channel block, whereas Zn2+
induces slow block of A
channels, and the binding site for
Zn2+ could be deep in the channel's conductive pathway
(35).
One proposed molecular channel model suggests that the A(1-40)-formed
channel is located asymmetrically within the membrane
(19). This asymmetry is
reflected at the putative entrances to the aqueous pore, which has three
histidine residues (His6, His13, and His14)
and several anionic residues including Asp7 and Glu11.
It is thought that metalloproteases bind Zn2+ and Cu2+
to these sites (3,
19). This is consistent with
the primary structure of A
(1-42), which contains two separate local
sequences containing histidine
(13). The local sequence FRHDS
contains His6, whereas the other local sequence, EVHHQ, contains
His13 and His14. The A
(1-40)-formed channel has
rings of His6 and Asp7 surrounding one pore entrance.
Successive rings of Glu11, His13, and His14
encircle the other entrance
(3). There is evidence to show
that His13 is crucial in the zinc ion-induced aggregation of
A
(39). It is
interesting to note that His at position 13 is also involved in mediating the
binding of Cu2+ and Zn2+ in nonnative states of
2-microglobulin, which is deposited as amyloid plaques in the joint
space that underlies the debilitating complications of long-term hemodialysis
(20). Additionally, the
oligomeric
2-microglobulin channels are also blocked with
Zn2+ (22).
We propose that in vivo membrane damage results from the interaction of
age- and mutation-induced malfunctioned proteins with lipid membranes.
A(1-42) is capable of inducing membrane damage, as deduced from
formation of channels, in the absence of an increase in the background traces
of Cu2+. The formation of a Cu2+-A
(1-42) channel
complex may act as an additional mechanism affecting Cu2+
homeostasis, which normally prevents the production of aberrant reactive
oxygen species, and thus accentuating the neurotoxic effects of
A
(1-42).
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DISCLOSURES |
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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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.
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REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
2. Arispe N,
Pollard HB, and Rojas E. Giant multilevel cation channels formed by
Alzheimer disease amyloid beta-protein [A- (1-40)] in bilayer membranes.
Proc Natl Acad Sci USA 90:
10573-10577, 1993.[Abstract]
3. Arispe N,
Pollard HB, and Rojas E. Zn2+ interaction with Alzheimer
amyloid beta protein calcium channels. Proc Natl Acad Sci
USA 93:
1710-1715, 1996.
4. Arispe N, Rojas E, and Pollard HB. Alzheimer disease amyloid beta protein forms calcium channels in bilayer membranes: blockade by tromethamine and aluminum. Proc Natl Acad Sci USA 90: 567-571, 1993.[Abstract]
5. Atwood CS, Moir
RD, Huang X, Scarpa RC, Bacarra NM, Romano DM, Hartshorn MA, Tanzi RE, and
Bush AI. Dramatic aggregation of Alzheimer A by Cu(II) is induced by
conditions representing physiological acidosis. J Biol
Chem 273:
12817-12826, 1988.
6. Atwood CS, Scarpa RC, Huang X, Moir RD, Jones WD, Fairlie DP, Tanzi RE, and Bush AI. Characterization of copper interactions with Alzheimer amyloid beta peptides: identification of an attomolar-affinity copper binding site on amyloid beta1-42. J Neurochem 75: 1219-1233, 2000.[ISI][Medline]
7. Auerbach A and
Akk G. Desensitization of mouse nicotinic acetylcholine receptor channels.
A two-gate mechanism. J Gen Physiol
112: 181-197,
1998.
8. Barry PH. JPCalc: a software package for calculating liquid junction potential corrections in patch-clamp, intracellular, epithelial and bilayer measurements and for correcting junction potential measurements. J Neurosci Methods 51: 107-116, 1994.[ISI][Medline]
9. Behl C, Davis JB, Lesley R, and Schubert D. Hydrogen peroxide mediates amyloid beta protein toxicity. Cell 77: 817-827, 1994.[ISI][Medline]
10. Bhatia R, Lin
H, and Lal R. Fresh and globular amyloid beta protein (1-42) induces rapid
cellular degeneration: evidence for AP channel-mediated cellular
toxicity. FASEB J 14:
1233-1243, 2000.
11. Bush AI. Metals and neuroscience. Curr Opin Chem Biol 4: 184-191, 2000.[ISI][Medline]
12. Bush AI. Therapeutic targets in the biology of Alzheimer's disease. Curr Opin Psych 14: 341-348, 2001.[ISI]
13. Bush AI, Pettingell WH, Multhaup G, d'Paradis M, Vonsattel JP, Gusella JF, Beyreuther K, Masters CL, and Tanzi RE. Rapid induction of Alzheimer A beta amyloid formation by zinc. Science 265: 1464-1467, 1994.[ISI][Medline]
14. Cherny RA, Atwood CS, Xilinas ME, Gray DN, Jones WD, McLean CA, Barnham KJ, Volitakis I, Fraser FW, Kim Y, Huang X, Goldstein LE, Moir RD, Lim JT, Beyreuther K, Zheng H, Tanzi RE, Masters CL, and Bush AI. Treatment with a copper-zinc chelator markedly and rapidly inhibits beta-amyloid accumulation in Alzheimer's disease transgenic mice. Neuron 30: 665-676, 2001.[ISI][Medline]
14. Colquhoun D and Hawkes AG. Fitting and statistical analysis of single-channel recording. In: Single Channel Recording, edited by Sakmann B and Neher E. New York: Plenum, 1983, p. 135-175.
15. Curtain CC, Ali
F, Smith DG, Bush AI, Masters CL, and Barnham KJ. Metal ions, pH, and
cholesterol regulate the interactions of Alzheimer's disease amyloid-beta
peptide with membrane lipid. J Biol Chem
278: 2977-2982,
2003.
16. Curtain CC, Ali
F, Volitakis I, Cherny RA, Norton RS, Beyreuther K, Barrow CJ, Masters CL,
Bush AI, and Barnham KJ. Alzheimer's disease amyloid-beta binds copper and
zinc to generate an allosterically ordered membrane-penetrating structure
containing superoxide dismutase-like subunits. J Biol
Chem 276:
20466-20473, 2001.
17. Davis DP, Gallo G, Vogen SM, Dul JL, Sciarretta KL, Kumar A, Raffen R, Stevens FJ, and Argon Y. Both the environment and somatic mutations govern the aggregation pathway of pathogenic immunoglobulin light chain. J Mol Biol 313: 1021-1034, 2001.[ISI][Medline]
18. Dilger JP,
Boguslavsky R, Barann M, Katz T, and Vidal AM. Mechanisms of barbiturate
inhibition of acetylcholine receptor channels. J Gen
Physiol 109:
401-414, 1997.
19. Durell SR, Guy HR, Arispe N, Rojas E, and Pollard HB. Theoretical models of the ion channel structure of amyloid beta-protein. Biophys J 67: 137-145, 1994.
20. Eakin CM, Knight JD, Morgan CJ, Gelfand MA, and Miranker AD. Formation of a copper specific binding site in non-native states of beta-2-microglobulin. Biochemistry 41: 10646-10656, 2002.[ISI][Medline]
21. Fraser SP, Suh YH, Chong YH, and Djamgoz MB. Membrane currents induced in Xenopus oocytes by the C-terminal fragment of the beta-amyloid precursor protein. J Neurochem 66: 2034-2040, 1996.[ISI][Medline]
22. Hirakura Y, Kagan BL. Pore formation by beta-2-microglobulin: a mechanism for the pathogenesis of dialysis associated amyloidosis. Amyloid 8: 94-100, 2001.[Medline]
23. Hirakura Y, Lin
MC, and Kagan BL. Alzheimer amyloid A1-42 channels: effects of
solvent, pH, and Congo red. J Neurosci Res
57: 458-466,
1999.[ISI][Medline]
24. Hirakura Y,
Satoh Y, Hirashima N, Suzuki T, Kagan BL, and Kirino Y. Membrane
perturbation by the neurotoxic Alzheimer amyloid fragment 25-35 requires
aggregation and
-sheet formation. Biochem Mol Biol
Int 46: 787-794,
1998.[ISI][Medline]
25. Huang X,
Cuajungco MP, Atwood CS, Hartshorn MA, Tyndall JD, Hanson GR, Stokes KC,
Leopold M, Multhaup G, Goldstein LE, Scarpa RC, Saunders AJ, Lim J, Moir RD,
Glabe C, Bowden EF, Masters CL, Fairlie DP, Tanzi RE, and Bush AI. Cu(II)
potentiation of Alzheimer A neurotoxicity. Correlation with cell-free
hydrogen peroxide production and metal reduction. J Biol
Chem 274:
37111-37116, 1999.
26. Jobling MF, Huang X, Stewart LR, Barnham KJ, Curtain CC, Volitakis I, Perugini M, White AR, Cherny RA, Masters CL, Barrow CJ, Collins SJ, Bush AI, and Cappai R. Copper and zinc binding modulates the aggregation and neurotoxic properties of the prion peptide PrP106-126. Biochemistry 40: 8073-8084, 2001.[ISI][Medline]
27. Kardos J, Kovacs I, Hajos F, Kalman M, and Simonyi M. Nerve endings from rat brain release copper upon depolarization. A possible role in regulating neuronal excitability. Neurosci Lett 103: 139-144, 1989.[ISI][Medline]
28. Kawahara M,
Kuroda Y, Arispe N, and Rojas E. Alzheimer's disease -amyloid, human
islet amylin, and prion protein fragment evoke intracellular free calcium
elevations by a common mechanism in hypothalamic GnRH neuronal cell line.
J Biol Chem 275:
14077-14083, 2000.
29. Kawahara M, Arispe N, Kuroda Y, and Rojas E. Alzheimer's disease amyloid beta-protein forms Zn2+-sensitive, cation-selective channels across excised membrane patches from hypothalamic neurons. Biophys J 73: 67-75, 1997.[Abstract]
30. Kim HJ, Suh YH, Lee MH, and Ryu PD. Cation selective channels formed by a C-terminal fragment of beta-amyloid precursor protein. Neuroreport 10: 1427-1431, 1999.[ISI][Medline]
31. Kourie JI. Vagaries of artificial bilayers and gating modes of the SCl channel from the sarcoplasmic reticulum of skeletal muscle. J Membr Sci 116: 221-227, 1996.[ISI]
32. Kourie JI. Mechanisms of amyloid beta protein-induced modification in ion transport systems: Implications for neurodegenerative diseases. Cell Mol Neurobiol 21: 173-213, 2001.[ISI][Medline]
33. Kourie JI, Culverson AL, Farrelly PV, Henry CL, and Laohachai KN. Heterogeneous amyloid-formed ion channels as a common cytotoxic mechanism: implications for therapeutic strategies against amyloidosis. Cell Biochem Biophys 36: 191-207, 2002.[ISI][Medline]
34. Kourie JI, Farrelly PV, and Henry CL. Channel activity of deamidated isoforms of prion protein fragment 106-126 in planar lipid bilayers. J Neurosci Res 66: 214-220, 2001.[ISI][Medline]
35. Kourie JI, Henry CL, and Farrelly PV. Diversity of amyloid beta protein fragment [1-40]-formed channels. Cell Mol Neurobiol 21: 255-284, 2001.[ISI][Medline]
36. Kourie JI, Laver DR, Junankar PR, Gage PW, and Dulhunty AF. Characteristic of two types of chloride channel in sarcoplasmic reticulum vesicles from rabbit skeletal muscle. Biophys J 70: 202-221, 1996.[Abstract]
37. Lin H, Bhatia
R, and Lal R. Amyloid protein forms ion channels: Implications for
Alzheimer's disease pathophysiology. FASEB J
15: 2433-2444,
2001.
38. Lin H, Zhu YJ, and Lal R. Amyloid beta protein (1-40) forms calcium-permeable. Zn2+-sensitive channel in reconstituted lipid vesicles. Biochemistry 38: 11189-11196, 1999.[ISI][Medline]
39. Liu ST, Howlett
G, and Barrow CJ. Histidine-13 is a crucial residue in the zinc
ion-induced aggregation of A peptide of Alzheimer's disease.
Biochemistry 38:
9373-9378, 1999.[ISI][Medline]
40. Miller C and Racker E. Ca++-induced fusion of fragmented sarcoplasmic reticulum with artificial planar bilayers. J Membr Biol 30: 283-300, 1976.[ISI][Medline]
41. Mirzabekov T, Lin M, Yuan W, Marshall PJ, Carman M, Tomaselli K, Lieberburg I, and Kagan B. Channel formation in planar lipid bilayers by a neurotoxic fragment of the beta-amyloid peptide. Biochem Biophys Res Commun 202: 1142-1148, 1994.[ISI][Medline]
42. Miura T, Suzuki K, Kohata N, and Takeuchi H. Metal binding modes of Alzheimer's amyloid beta-peptide in insoluble aggregates and soluble complexes. Biochemistry 39: 7024-7031, 2000.[ISI][Medline]
43. Mobashery N, Nielsen C, and Andersen OS. The conformational preference of gramicidin channels is a function of lipid bilayer thickness. FEBS Lett 412: 15-20, 1997.[ISI][Medline]
44. Opazo C, Huang
X, Cherny RA, Moir RD, Roher AE, White AR, Cappai R, Masters CL, Tanzi RE,
Inestrosa NC, and Bush AI. Metalloenzyme-like activity of Alzheimer's
disease beta-amyloid. Cu-dependent catalytic conversion of dopamine,
cholesterol, and biological reducing agents to neurotoxic
H2O2. J Biol Chem
277: 40302-40308,
2002.
45. Patlak JB. Measuring kinetics of complex single ion channel data using mean-variance histograms. Biophys J 65: 29-42, 1993.[Abstract]
46. Pollard HB, Arispe N, and Rojas E. Ion channel hypothesis for Alzheimer amyloid peptide neurotoxicity. Cell Mol Neurobiol 15: 513-526, 1995.[ISI][Medline]
47. Pollard HB,
Rojas E, and Arispe N. A new hypothesis for the mechanism of amyloid
toxicity, based on the calcium channel activity of amyloid beta protein
(AP) in phospholipid bilayer membranes. Ann NY Acad
Sci 695: 165-168,
1993.[Abstract]
48. Qi JS and Qiao JT. Amyloid beta-protein fragment 31-35 forms ion channels in membrane patches excised from rat hippocampal neurons. Neuroscience 105: 845-852, 2001.[ISI][Medline]
49. Rhee SK, Quist
AP, and Lal R. Amyloid beta protein-(1-42) forms calcium-permeable
Zn2+-sensitive channel. J Biol Chem
273: 13379-13382,
1998.
50. Sanderson KL, Butler L, and Ingram VM. Aggregates of a beta-amyloid peptide are required to induce calcium currents in neuron-like human teratocarcinoma cells: relation to Alzheimer's disease. Brain Res 744: 7-14, 1997.[ISI][Medline]
51. Simmons MA and Schneider CR. Amyloid beta peptides act directly on single neurons. Neurosci Lett 150: 133-136, 1993.[ISI][Medline]
52. Spitzmaul G,
Dilger DP, and Bouzat C. The non-competitive inhibitor quinacrine modifies
the desensitization kinetics of muscle acetylcholine receptors. Mol
Pharmacol 60:
235-243, 2001.
53. Suzuki N, Cheung TT, Cai XD, Odaka A, Otvos L Jr, Eckman C, Golde TE, and Younkin SG. An increased percentage of long amyloid beta protein secreted by familial amyloid beta protein precursor (beta APP717) mutants. Science 264: 1336-1340, 1994.[ISI][Medline]
54. Uversky VN, Li
J, and Fink AL. Metal-triggered structural transformations, aggregation,
and fibrillation of human alphasynuclein. A possible molecular NK between
Parkinson's disease and heavy metal exposure. J Biol
Chem 276:
44284-44296, 2001.
55. Vargas J,
Alarcón JM, and Rojas E. Displacement currents associated with the
insertion of Alzheimer disease amyloid beta-peptide into planar bilayer
membranes. Biophys J 79:
934-944, 2000.
56. Yankner BA, Duffy LK, and Kirschner DA. Neurotrophic and neurotoxic effects of amyloid beta protein: reversal by tachykinin neuropeptides. Science 250: 279-282, 1990.[ISI][Medline]
57. Zhu YJ, Lin H,
and Lal R. Fresh and nonfibrillar amyloid beta protein(1-40) induces rapid
cellular degeneration in aged human fibroblasts: evidence for
AP-channel-mediated cellular toxicity. FASEB J
14: 1244-1254,
2000.