N-benzhydryl quinuclidine compounds are a potent and Src kinase-independent inhibitor of NALCN channels

Abstract

Background and Purpose NALCN is a Na(+)leak, GPCR-activated channel that regulates the resting membrane potential and neuronal excitability. Despite numerous possible roles for NALCN in both normal physiology and disease processes, lack of specific blockers hampers further investigation. Experimental Approach The effect ofN-benzhydryl quinuclidine compounds on NALCN channels was demonstrated using whole-cell patch-clamp recordings in HEK293T cells overexpressing NALCN and acutely isolated nigral dopaminergic neurons that express NALCN endogenously. Src kinase activity was measured using a Src kinase assay kit, and voltage and current-clamp recordings from nigral dopaminergic neurons were used to measure NALCN currents and membrane potentials. Key Results N-benzhydryl quinuclidine compounds inhibited NALCN channels without affecting TRPC channels, another important route for Na(+)leak. In HEK293T cells overexpressing NALCN,N-benzhydryl quinuclidine compounds potently suppressed muscarinic M(3)receptor-activated NALCN currents. Structure-function relationship studies suggest that the quinuclidine ring with a benzhydryl group imparts the ability to inhibit NALCN currents regardless of Src family kinases. Moreover,N-benzhydryl quinuclidine compounds inhibited not only GPCR-activated NALCN currents but also background Na(+)leak currents and hyperpolarized the membrane potential in native midbrain dopaminergic neurons that express NALCN endogenously. Conclusion and Implications These findings suggest thatN-benzhydryl quinuclidine compounds have a pharmacological potential to directly inhibit NALCN channels and could be a useful tool to investigate functions of NALCN channels.