Histological demonstration of voltage dependent calcium channels on calcitonin gene-related peptide-immunoreactive nerve fibres in the mouse knee joint

The afferent (excitability) and efferent functions (release of neuropeptides) of primary afferent nerve fibres are based on CA(2+)-influx. The aim of the present study was to examine the presence of L- and N-type CA(2+)-channels at sensory nerve fibres in the mouse knee joint capsule. Specific fluorescent labelled channel blockers and antisera against these channel subtypes were combined with an immunohistochemical staining for Calcitonin gene-related peptide (CGRP), a neuropeptide that is widely distributed in primary afferents. There was a nearly complete colocalisation of CGRP immunoreactivity and the binding of omega-conotoxin GVIA (toxin VIA of Conus geographus or BODIPY-verapamil (BODIPY(R) FL verapamil, hydrochloride) demonstrating the presence of N-type and L-type CA(2+)-channels, respectively. These data were further confirmed by identical results obtained after an immunohistochemical demonstration of the two channel subtypes at the peptidergic nerve fibres.