Suppressive Effects of Beta Amyloid Peptides (1-42) and (25-35) on Kv1.1 Channel Activity

Abstract

Beta amyloid (Aβ) peptides have long been implicated in Alzheimer's Disease (AD) pathology, linking them to disruption of: Ca2+ homeostasis, synaptic communication, and long-term potentiation (LTP). But the mechanism(s) underlying these effects are still unclear. Because Kv1.1 and related channels are activated during an action potential, regulate depolarization-produced Ca2+ influx, and inhibition of Kv1 channels can be neurotoxic, we speculate that Aβ-suppression of Kv1 channels may be an early event in AD pathogenesis. Using murine Kv1.1 channels expressed in Xenopus oocytes, we have observed the effects of Aβ(1-42) and the “core” peptide (25-35) on both macro- and micro-scopic currents. Both the bath application of Aβ(1-42) and Aβ(25-35) produced 40-50% suppression of macroscopic Kv1.1 current within 30 m. Suppression of Kv1.1 by Aβ(1-42) was partially dependent on intracellular Ca2+ and PP2B, showing only ∼25% reduction when cells were loaded with BAPTA-AM or exposed to the PP2B-inhibitor cyclosporine A (CsA). Patch-clamp results suggested that Aβ-suppression of Kv1.1 involved both PP2B-dephosphorylation and direct protein-protein interaction of Aβ with Kv1.1. Exposure of the intracellular face of Kv1.1 channels in ripped-off oocyte patches to either catalytically-active PP2B, or Aβ(1-42), produced gradual reductions in p(open), followed by the abrupt disappearance of Kv1.1 activity. Using “tip-dip” artificial membrane methods, Aβ(25-35) exposure eliminated Kv1.1 channel activity when applied to the channel intracellular face. Kv1.1 channels have also been incorporated into Black Lipid Membranes (BLMs), and we are currently assessing the effects of exposure of Aβ to both intra- and extra-cellular faces of Kv1.1. Suppression of presynaptic Kv1.1 (and related) channels could lead to enhanced action potentials, thus allowing greater influx of Ca2+ and subsequent increase in glutamate release. Postsynaptically, the increased glutamate release, through activation of AMPA and NMDA receptors, may contribute to excitotoxicity.