Suppression of a neocortical potassium channel activity by intracellular amyloid-β and its rescue with homer1a

It is proposed that intracellular amyloid-β (Aβ), before extracellular plaque formation, triggers cognitive deficits in Alzheimer disease (AD). Here we report how intracellular Aβ affects neuronal properties. This was done by injecting Aβ protein into rat and mouse neocortical pyramidal cells through whole-cell patch pipettes and by using 3xTgADmodel mice, in which intracellularAβ is accumulated innately. In rats, intracellular application of a mixedAβ_1-42 preparation containing both oligomers and monomers, but not a monomeric preparation of Aβ_1-40, broadened spike width and augmented Ca²⁺ influx via voltage-dependent Ca²⁺ channels in neocortical neurons. Both effects were mimicked and occluded by charybdotoxin, a blocker of large-conductance Ca²⁺-activated K⁺ (BK) channels, and blocked by isopimaric acid, a BK channel opener. Surprisingly, augmented Ca²⁺ influx was caused by elongated spike duration, but not attributable to direct Ca²⁺channel modulation by Aβ_1-42. The Aβ_1-42-induced spike broadening was blocked by electroconvulsive shock (ECS), which we previously showed to facilitate BK channel opening via expression of the scaffold protein Homer1a. In young 3xTg and wild mice, we confirmed spike broadening by Aβ_1-42, which was again mimicked and occluded by charybdotoxin and blocked by ECS. In Homer1a knock-out mice, ECS failed to block the Aβ_1-42 effect. Single-channel recording on BK channels supported these results. These findings suggest that the suppression of BK channels by intracellular Aβ_1-42 is a possible key mechanism for early dysfunction in the AD brain, which may be counteracted by activity-dependent expression of Homer1a.