Abstract
Tachykinins are present in enteric nerves of the gastrointestinal tract and cause contraction of esophageal smooth muscle; however, the mechanisms involved are not understood. Our aim was to characterize tachykinin signaling in human esophageal smooth muscle. We investigated functional effects of tachykinins on human esophageal smooth muscle using tension recordings and isolated cells, receptor expression with reverse transcription (RT)-polymerase chain reaction (PCR) and immunoblotting, intracellular Ca2+ responses using fluorescent indicator dyes, and membrane currents with patch-clamp electrophysiology. The mammalian tachykinins [substance P and neurokinin (NK) A and NKB] elicited concentration-dependent contractions of human esophageal smooth muscle. These responses were not affected by muscarinic receptor or neuronal blockade indicating a direct effect on smooth muscle cells (SMCs). Immunofluorescence and RT-PCR identified tachykinin receptors (NK1, NK2, and NK3) on SMCs. Contraction was mediated through a combination of Ca2+ release from intracellular stores and influx through L-type Ca2+ channels. NK2 receptor blockade inhibited the largest proportion of tachykinin-evoked responses. NKA evoked a nonselective cation current (INSC) with properties similar to that elicited by muscarinic stimulation. The following paradigm is suggested: tachykinin receptor binding to SMCs releases Ca2+ from stores along with activation of INSC, which in turn results in membrane depolarization, L-type Ca2+ channel opening, rise of Ca2+ concentration, and contraction. These studies reveal new aspects of tachykinin signaling in human esophageal SMCs. Excitatory tachykinin pathways may represent targets for pharmacological intervention in disorders of esophageal dysmotility.
Footnotes
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This work was supported by Canadian Institutes of Health Research, by a Ontario Ministry of Health Career Scientist Award (to H.G.P.), and by a CIHR M.D./Ph.D. Studentship (to J.R.K.).
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.106.104034.
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ABBREVIATIONS: SP, substance P; NK, neurokinin; ACh, acetylcholine; EB, esophageal body; ICC, interstitial cell(s) of Cajal; SMC, smooth muscle cell; INSC, nonselective cation current; CM, circular muscle; LM, longitudinal muscle; RT, reverse transcription; PCR, polymerase chain reaction; PBS, phosphate-buffered saline; SR48968, (S)-N-methyl-N[4-(4-acetyl-amino-4-phenylpiperi-dino)-2-(3,4-dichloro-phenyl)butyl]benzamide; SR140333, (S)-1-[2-[3-(3,4-dichlorphenyl)-1 (3-isopropoxy-phenylacetyl)piperidin-3yl]ethyl]-4-phenyl-1 azaniabicyclo [2.2.2] octane chloride; SR142801, (R)-(N)-[1-[3-[1-benzoyl-3-(3,4-dichlorophenyl)piperidin-3-yl]propyl]-4-phenylpiperidin-4-yl]-N-methylacetamide; TTX, tetrodotoxin; [Ca2+]i, intracellular free Ca2+ concentration; CPA, cyclopiazonic acid; bp, base pair(s); CCh, carbachol.
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↵ The online version of this article (available at http://jpet.aspetjournals.org) contains supplemental material.
- Received March 3, 2006.
- Accepted May 18, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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