Activation of neurokinin 1 receptors on interstitial cells of Cajal of the guinea-pig small intestine by substance P |
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Authors: | S T Lavin B R Southwell R Murphy K M Jenkinson J B Furness |
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Institution: | (1) Department of Anatomy and Cell Biology, University of Melbourne, Parkville, Victoria 3052, Australia e-mail John.Furness@anatomy.unimelb.edu.au Tel. +61 3 9344 5804; fax +61 3 9347 5219, AU |
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Abstract: | The aims of this work were to determine whether cells that are similar to the interstitial cells of Cajal (ICC) and have
immunoreactivity for the neurokinin 1 (NK1) receptor are indeed ICC; to determine whether the agonist, substance P, binds
to and activates the receptor on presumptive ICC; and to investigate the relationship between substance P-immunoreactive nerve
fibres and ICC. ICC at the level of the myenteric plexus and in the deep muscular plexus in the duodenum and ileum of the
guinea-pig were investigated. Immunoreactivities for the ICC marker, Kit, and the NK1 receptor were colocalised in ICC of
the myenteric and deep muscular plexuses. In tissue fixed immediately after its removal from the animal, NK1 receptor-immunoreactive
ICC were found at the level of the myenteric plexus in the duodenum, but not in the ileum, and in the deep muscular plexus
in the duodenum and ileum. The majority of receptor immunoreactivity was on the cell surface. ICC were exposed to substance
P (10–7 M), initially at 4°C for 1 h to allow the agonist to bind, followed by incubation at 37°C to allow receptor internalisation
to proceed. Exposure to substance P caused the NK1 receptor immunoreactivity to aggregate in clumps in the cytoplasm of ICC
of the myenteric and deep muscular plexuses, including the ICC of the myenteric plexus of the ileum, where NK1 receptor immunoreactivity
was not seen if tissue was not exposed to substance P. Substance P, to which the fluorescent label, cyanine 3.18 (Cy-3), was
coupled, bound to the ICC. The Cy-3-substance P was internalised with the receptor following warming to 37°C. Many, but not
all, ICC were closely apposed by nerve fibres with immunoreactivity for substance P. It is concluded that the NK1 receptor
immunoreactivity on ICC represents receptor that is functional in the sense that it binds the natural agonist substance P
and undergoes agonist-induced internalisation. ICC are likely to receive excitatory innervation from the close approaches
of tachykinin-containing nerve fibres.
Accepted: 10 March 1998 |
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