Background and Purpose: Parkinson’s disease (PD) is clinically defined by the presence of the cardinal motor symptoms, which are associated with a loss of dopaminergic nigrostriatal neurons in the substantia nigra pars compacta (SNpc). While SNpc neurons serve as the prototypical cell-type to study cellular vulnerability in PD, there is an unmet need to extent our efforts to other neurons at risk. The noradrenergic locus coeruleus (LC) represents one of the first brain structures affected in Parkinson’s disease (PD) and plays not only a crucial role for the evolving non-motor symptomatology, but it is also believed to contribute to disease progression by efferent noradrenergic deficiency. Experimental Approach: Therefore, we sought to characterized the electrophysiological properties of LC neurons in two distinct PD models: (1) in an in vivo mouse model of focal α-synuclein overexpression; and (2) in an in vitro rotenone-induced PD model. Key Results: Despite the fundamental differences of these two PD models, α-synuclein overexpression as well as rotenone exposure led to an accelerated autonomous pacemaker frequency of LC neurons, accompanied by severe alterations of the afterhyperpolarization amplitude. On the mechanistic side, we identified small-conductance Ca2+-activated K+ (SK) channels as crucial mediators of the increased LC neuronal excitability and demonstrate that pharmacological activation of these channels is sufficient to prevent increased LC pacemaking and subsequent neurodegeneration following in vitro rotenone exposure. Conclusion and Implications: These findings highlight the important role of SK channels in PD by linking α-synuclein- and rotenone-induced LC pathology to SK channel dysfunction.

Background and Purpose: Local anesthetics block sodium and a variety of potassium channels. Although previous studies identified a residue in the pore signature sequence together with three residues in the S6 segment as a putative binding site, the precise molecular basis of Kv potassium channel inhibition by local anesthetics remained unknown. Kv crystal structures predict that some of these residues point away from the central cavity and face into a drug binding site called ‘side pockets´. Thus, the question arises whether the binding site of local anesthetics is exclusively located in the central cavity or also involves the ‘side pockets´. Experimental Approach: A systematic functional alanine mutagenesis approach, scanning 58 mutants, in concert with in silico docking experiments and molecular dynamics simulations were utilized to elucidate the binding site of bupivacaine and ropivacaine. Key Results: Kv1.5 inhibition by local anesthetics requires binding to the central cavity and the ‘side pockets´, where the latter requires interactions with residues of the S5 and the backside of the S6 segment. Mutations in the ‘side pockets´ remove stereoselectivity of Kv1.5 inhibition by bupivacaine. Strikingly, while we found that binding to the ‘side pockets´ is conserved for the different local anesthetics, the binding mode in the central cavity and the ‘side pockets´ shows considerable variations. Conclusion and Implications: Local anesthetics bind to the central cavity and the ‘side pockets´ which provides a crucial key for the molecular understanding of their Kv channel affinity and stereoselectivity, as well as their spectrum of side effects.