Immunohistochemical and electrophysiological evidence for ω-conotoxin-sensitive calcium channels in unmyelinated C-fibres of biopsied human sural nerve

In vitro electrophysiological measurements of Ca²⁺ potentials in human sural nerve fascicles revealed that Ca²⁺ conductances might be present on unmyelinated C-fibres. Furthermore, these Ca²⁺ potentials were partially blocked by ω-conotoxin, a calcium antagonist for the N-type Ca²⁺ channels. Therefore, immunohistochemical staining with indirect immunofluorescent ω-conotoxin GVIA was used to localize N-type Ca²⁺ channels in intact and in enzymatically dissociated human sural nerve fascicles. Densities of toxin binding sites were highly heterogeneous throughout the different nerve fascicles investigated and putative N-type Ca²⁺ channels were localized in about 20% of the unmyelinated C-fibres. Myelinating Schwann cells as well as enzymatically demyelinated axons displayed no specific binding indicating the absence of N-type Ca²⁺ channels.