It might be thought likely that these channels would be localised especially at sites in the sensory Imazapic endings where action potentials are generated and where they could be particularly effective in regulating the firing rate. Heminodes, of which there may be several in any one sensory ending and which are located in preterminal branches, are thought to be the most important such sites, but they were not amenable to study in the present work where we have concentrated on the sensory terminals and associated accessory cells. We have carried out preliminary observations on the immunohistochemistry of BK, which indicate that it is not present in the sensory terminals of either muscle spindles or lanceolate endings, but we have yet to investigate whether immunoreactivity to BK or SK can be detected at heminodes. In the light of the previous consideration, our clear evidence for SK2 expression throughout the sensory terminals of both muscle spindles and lanceolate endings is all the more remarkable. In the very large terminals of muscle spindles much of the immunoreactivity was found within the terminals, though it was not completely colocalised with SYN, the SLV marker. Any SK2 localised internally is presumably sequestered in a reserve pool, as its functional site must surely be the sensory terminal membrane. The sensory terminals are, of course, thought to be the sites where receptor potentials are produced in response to the mechanical deformation of the terminals resulting in gating of stretch-activated channels in their membranes. Hunt et al. succeeded in recording muscle-spindle receptor potentials from the parent axons, rather than the inaccessible terminals, by blocking action potentials with tetrodotoxin. In lanceolate endings spatial resolution with immunofluorescence was rarely sufficient to Ritodrine HCl separate clearly the immunoreactivity of the sensory terminals and their associated SGC processes, even in single confocal planes. The quantitative data analysis must therefore be interpreted using additional qualitative information, provided by examination of SGC bodies and sensory axons in the region of the hair follicles deep to the palisade endings.