Suppression of Kv1.1 Channel Activity by Beta-Amyloid Peptides Involves both Intracellular Calcium-Signaling and Direct Peptide-Peptide Interactions

Abstract

Past studies indicate that Aβ's role(s) in Alzheimer's disease (AD) pathogenesis involves disruption of Ca2+ homeostasis, synaptic communication, and impairment of learning- and memory-related synaptic plasticity [e.g., hippocampal LTP]. 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 have speculated that Aβ-suppression of Kv1 channels could contribute to AD pathology. The bath application of either Aβ(1-42) or “core” peptide Aβ(25-35) produced 40-50% suppression of macroscopic Kv1.1 current within 30 m (murine Kv1.1 channels expressed in Xenopus oocytes). Little or no suppression was produced by reverse peptide Aβ(40-1) or solvent control. Strong suppression of Kv1.2 channels by Aβ(1-42) was also observed. The 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). Membrane capacitance measurements and Western Blot analyses failed to detect any Aβ(1-42)-produced endocytosis of Kv1.1 channels, in contrast to clear endocytosis when large increases in intracellular calcium were produced by the ionophore A23187. Aβ-suppression of Kv1.1 involved both PP2B-dephosphorylation and direct protein-protein interaction of Aβ with Kv1.1 subunits. Exposure of the intracellular face of Kv1.1 channels in ripped-off oocyte patches to either purified catalytically-active PP2B, or Aβ(1-42), produced gradual reductions in p(open), followed by abrupt disappearance of Kv1.1 activity. The collective results from additional single-channel studies [involving “tip-dip”, and black lipid membranes (BLMs)] showed that direct application of Aβ peptides to individual Kv1.1 channels reduced channel activity, whether applied intra- or extra-cellularly. The suppressions produced by the shorter core fragment, Aβ(25-35), were clear but generally weaker than Aβ(1-42).