Emerging Concepts in Ion Channel Biophysics

Emerging Concepts in Ion Channel Biophysics

Poster Abstracts

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.

99