Cell adhesion molecule L1 contributes to neuronal excitability regulating the function of voltage-gated sodium channels

Abstract

L1 is a trans-membrane glycoprotein subserving neuron-neuron adhesion via homophilic and heterophilic interactions. Although experimental evidences have implicated L1 in axonal outgrowth, fasciculation and pathfinding, its contribution to voltage-gated sodium channels (NaChs) function and membrane excitability has remained unknown. Here, we show that firing rate, single cell spiking frequency and Na+ current density are all reduced in hippocampal excitatory neurons from L1-deficient mice both in culture and in slices, due to an overall reduced membrane expression of NaChs. Remarkably, normal firing activity was restored when L1 was reintroduced into L1-deficient excitatory neurons, indicating that abnormal firing patterns are not related to developmental abnormalities, but are a direct consequence of L1 deletion. Moreover, L1-deficiency leads to impairment of action potential (AP) initiation, most likely due to the loss of the interaction of L1 with Ankyrin G that produces the delocalization of NaChs at the at the axonal initial segment. We conclude that L1 contributes to functional expression and localization of NaChs to the neuronal plasma membrane, ensuring correct initiation of AP and normal firing activity.