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Circular Muscle Contraction, Messenger Signalling And Localization Of Binding Sites For Neurokinin A In Human Sigmoid Colon
Author(s) -
Warner Fiona J,
Liu Lu,
Lubowski David Z,
Burcher Elizabeth
Publication year - 2000
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1046/j.1440-1681.2000.03363.x
Subject(s) - endocrinology , neurokinin a , medicine , muscularis mucosae , receptor , tachykinin receptor , substance p , muscle contraction , agonist , contraction (grammar) , biology , chemistry , carbachol , neuropeptide , stimulation
SUMMARY 1. Neurokinin (NK)A is the endogenous ligand for the tachykinin NK 2 receptor. In the present study, tachykinins and selective receptor agonists were tested as contractile agonists in human colon circular muscle and [ 125 I]‐NKA was used to localize binding sites in human colon. 2. In strips of circular muscle, removal of mucosa and submucosa significantly ( P < 0.05) increased the potency and the maximum response achieved by NKA. 3. The rank order of potency of tachykinin and selective receptor agonists in contracting circular muscle strips was NKA ≥ [Lys 5 ,MeLeu 9 ,Nle 10 ]NKA(4–10) ≥ neuropeptide (NP)γ≥ [βAla 8 ]NKA(4–10) » NKB > substance P (SP) » senktide ≈ [Pro 9 ]SP. 4. Specific binding sites for [ 125 I]‐NKA were densely localized over circular muscle and muscularis mucosae. Weak specific binding was seen on longitudinal muscle and taenia coli, whereas no binding sites were seen on mucosa, ganglia or blood vessels. 5. In circular muscle, the selective NK 2 receptor agonist [Lys 5 ,MeLeu 9 ,Nle 10 ]NKA(4–10) produced weak increases (maximum 37%) in inositol monophosphate formation with a pD 2 of 6.8±0.51 ( n = 3). Carbachol (100 μmol/L) was also a weak stimulant (maximum 45%). These agonists were over 10‐fold more efficacious in stimulation of inositol monophosphate in rat urinary bladder. 6. In conclusion, [ 125 I]‐NKA binding sites localized on human colon circular muscle were characterized as NK 2 receptors. Functionally, the tachykinin NK 2 receptor is mediating circular smooth muscle contraction. Although the human NK 2 receptor is coupled to the phosphatidylinositol pathway, other second messenger mechanisms may also operate in this tissue.