The b-secretase pathway is amyloidogenic in that consecutive cleavage of amyloid precursor protein (APP) by b-secretase (BACE1) and [gamma]-secretase can lead to the formation of amyloid plaques. Recent studies revealed two novel and unexpected substrates of BACE1, namely the b2 and b4 subunits of voltage-gated sodium channels (JBC 280:23009-17, 2005). Does the cleavage of b subunits by BACE1 affect the electrophysiological properties of sodium channels? We explored this question using whole-cell recordings from HEK293 cells expressing the Nav1.2asubunit alone or in combination with the b2 subunit and BACE1. Co-expression with b2 shifted the activation curve of Nav1.2a by about 13 mV in the negative direction. The negative shift was significantly, but not completely reversed when BACE1 was also co-expressed. The effect of BACE1 on the activation curve was abrogated by the b-secretase inhibitor, compound 3 (C3). The electrophysiological findings from HEK293 cells were corroborated by subsequent Western blot analysis which showed cleavage of b2 subunits by BACE1 and a decrease of cleavage in the presence of C3. These results suggest that by altering sodium channel gating BACE1 might possibly affect neuronal excitability. (1)Biochemistry, Univ Kiel, Germany; (2)RIKEN Brain Science Japan; (3) Neuronal Cell Biol. Lab., CME, KU Leuven, Belgium