Tumour necrosis factor α activates nuclear factor κB signalling to reduce N‐type voltage‐gated Ca2+ current in postganglionic sympathetic neurons

Inflammation has profound effects on the innervation of affected tissues, including altered neuronal excitability and neurotransmitter release. As Ca2+ influx through voltage‐gated Ca2+ channels (VGCCs) is a critical determinant of excitation–secretion coupling in nerve terminals, the aim of this study was to characterize the effect of overnight incubation in the inflammatory mediator tumour necrosis factor α (TNFα; 1 nm) on VGCCs in dissociated neurons from mouse superior mesenteric ganglia (SMG). Voltage‐gated Ca2+ currents (ICa) were measured using the perforated patch clamp technique and the VGCC subtypes present in SMG neurons were estimated based on inhibition by selective VGCC blockers: ω‐conotoxin GVIA (300 nm; N‐type), nifedipine (10 μm; L‐type), and ω‐conotoxin MVIIC (300 nm; N‐, P/Q‐type). We used intracellular Ca2+ imaging with Fura‐2 AM to compare Ca2+ influx during depolarizations in control and TNFα‐treated neurons. TNF receptor and VGCC mRNA expression were measured using PCR, and channel α subunit (CaV2.2) was localized with immunohistochemistry. Incubation in TNFα significantly decreased ICa amplitude and depolarization‐induced Ca2+ influx. The reduction in ICa was limited to ω‐conotoxin GVIA‐sensitive N‐type Ca2+ channels. Depletion of glial cells by incubation in cytosine arabinoside (5 μm) did not affect ICa inhibition by TNFα. Preincubation of neurons with SC‐514 (20 μm) or BAY 11‐7082 (1 μm), which both inhibit nuclear factor κB signalling, prevented the reduction in ICa by TNFα. Inhibition of N‐type VGCCs following TNFα incubation was associated with a decrease in CaV2.2 mRNA and reduced membrane localization of CaV2.2 immunoreactivity. These data suggest that TNFα inhibits ICa in SMG neurons and identify a novel role for NF‐κB in the regulation of neurotransmitter release during inflammatory conditions with elevated circulating TNFα, such as Crohn's disease and Guillain‐Barré syndrome.