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Emerging Concepts in Ion Channel Biophysics
Poster Abstracts
99
27-POS
Board 27
Amyloid Beta Peptide Fragments 1-42 and 25-35 Suppress Kv1.1 Channel Activity
Joseph Farley
, Kristi DeBoeuf, Mohammad F. Islam.
n/a, Bloomington, USA.
Many studies have found that Aβ-peptides participate in the pathogenesis of Alzheimer’s
disease, leading to disruption of Ca
2+
homeostasis and eventual neurotoxicity. The mechanisms
underlying these effects remain unclear. We suggest that Aβ-inhibition of voltage-dependent K+
channel (e.g., Kv1.1) activity is among the earliest steps. We previously elucidated a pathway in
which Ca
2+
-dependent activation of PP2B, PKC, PTKs, and RhoA all contributed to rapid strong
suppression of Kv1.1 activity in
Xenopus
oocytes. This pathway is recruited by a variety of
stimuli that increase [Ca
2+
]
i
, including GPCRs that couple to Gq/11 –PLC, and Ca
2+
ionophore.
Because Kv1-family channels regulate depolarization and Ca
2+
influx, and inhibition of Kv1
channels can be neurotoxic, we speculate that Aβ-suppression of Kv1 channels could lead to
hyperexcitability, altered synaptic transmission, disrupted Ca
2+
homeostasis, and neurotoxicity.
We assessed the effects of the Aβ(1-42) peptide and the core fragment [Aβ(25-35)] on murine
Kv1.1 channels expressed in oocytes. Aβ(1-42) [10 nM -1 μM] produced dose-dependent
inhibition of Kv1.1 current, ~50% reductions within 30 m for 1 μM. Aβ suppression of Kv1.1
was partially Ca
2+
- and PP2B-dependent, being reduced by ~50% when cells were loaded with
BAPTA-AM, or exposed to the PP2B-inhibitor cyclosporine A. Patch-clamp results suggest that
Aβ-suppression of Kv1.1 involves both PP2B-dephosphorylation and direct protein-protein
interaction of Aβ with Kv1.1 channel subunits. Exposure of inside-out single Kv1.1 channels in
ripped-off oocyte patches to purified catalytically-active PP2B produced gradual reductions in
p
(open), followed by abrupt disappearance of Kv1.1 activity. Application of Aβ to the
intracellular face of Kv1.1 channels also produced dramatic reductions in
p
(open). We also
found that 2 μM of the toxic core Aβ(25-35) suppressed Kv1.1 currents by ~40%. Using “tip-
dip” artificial membranes, 1 μM Aβ(25-35) suppressed Kv1.1 channels when applied to the
intracellular face.