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Apu AS, Mondal A, Kitazawa T, Takemi S, Sakai T, Sakata I. Molecular cloning of motilin and mechanism of motilin-induced gastrointestinal motility in Japanese quail. Gen Comp Endocrinol 2016; 233:53-62. [PMID: 27179882 DOI: 10.1016/j.ygcen.2016.05.017] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Revised: 05/10/2016] [Accepted: 05/11/2016] [Indexed: 12/16/2022]
Abstract
Motilin, a peptide hormone produced in the upper intestinal mucosa, plays an important role in the regulation of gastrointestinal (GI) motility. In the present study, we first determined the cDNA and amino acid sequences of motilin in the Japanese quail and studied the distribution of motilin-producing cells in the gastrointestinal tract. We also examined the motilin-induced contractile properties of quail GI tracts using an in vitro organ bath, and then elucidated the mechanisms of motilin-induced contraction in the proventriculus and duodenum of the quail. Mature quail motilin was composed of 22 amino acid residues, which showed high homology with chicken (95.4%), human (72.7%), and dog (72.7%) motilin. Immunohistochemical analysis showed that motilin-immunopositive cells were present in the mucosal layer of the duodenum (23.4±4.6cells/mm(2)), jejunum (15.2±0.8cells/mm(2)), and ileum (2.5±0.7cells/mm(2)), but were not observed in the crop, proventriculus, and colon. In the organ bath study, chicken motilin induced dose-dependent contraction in the proventriculus and small intestine. On the other hand, chicken ghrelin had no effect on contraction in the GI tract. Motilin-induced contraction in the duodenum was not inhibited by atropine, hexamethonium, ritanserin, ondansetron, or tetrodotoxin. However, motilin-induced contractions in the proventriculus were significantly inhibited by atropine and tetrodotoxin. These results suggest that motilin is the major stimulant of GI contraction in quail, as it is in mammals and the site of action of motilin is different between small intestine and proventriculus.
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Affiliation(s)
- Auvijit Saha Apu
- Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan
| | - Anupom Mondal
- Area of Life-NanoBio, Division of Strategy Research, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan
| | - Takio Kitazawa
- Comparative Animal Pharmacology Department of Veterinary Science, Rakuno Gakuen University, Ebetsu, Hokkaido 069-8501, Japan
| | - Shota Takemi
- Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan
| | - Takafumi Sakai
- Area of Life-NanoBio, Division of Strategy Research, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan
| | - Ichiro Sakata
- Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan.
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Takahashi H, Rikimaru K, Komatsu M, Uemoto Y, Suzuki K. Association between Motilin Receptor Gene Haplotypes and Growth Traits in Japanese Hinai-dori Crossbred Chickens. ASIAN-AUSTRALASIAN JOURNAL OF ANIMAL SCIENCES 2014; 27:316-23. [PMID: 25049957 PMCID: PMC4093263 DOI: 10.5713/ajas.2013.13500] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Revised: 11/16/2013] [Accepted: 10/10/2013] [Indexed: 12/29/2022]
Abstract
We previously identified quantitative trait loci (QTL) for body weight and average daily gain in a common region between ADL0198 (chr 1: 171.7 Mb) and ABR0287 (chr 1: 173.4 Mb) on chicken chromosome 1 in an F2 resource population produced by crossing low- and high-growth lines of the Hinai-dori breed. Motilin receptor (MLNR) is a candidate gene affecting growth traits in the region. In this study, we genotyped polymorphisms of the MLNR gene and investigated its association with growth traits in a Hinai-dori F2 intercross population. All the exons of the MLNR gene in the parental population were subjected to PCR amplification, nucleotide sequenced and haplotypes identified. To distinguish resultant diplotype individuals in the F2 population, a mismatch amplification mutation assay was performed. Three haplotypes (Haplotypes 1–3) were accordingly identified. Six genotypes produced by the combination of three haplotypes (Haplotype 1, 2, and 3) were examined in order to identify associations between MLNR haplotypes and growth traits. The data showed that Haplotype 1 was superior to Haplotype 2 and 3 in body weight at 10 and 14 weeks of age, average daily gain between 4 and 10 weeks, 10 and 14 weeks, and 0 and 14 weeks of age in female in F2 females. It was concluded that MLNR is a useful marker of growth traits and could be used to develop strategies for improving growth traits in the Hinai-dori breed.
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Affiliation(s)
- Hideaki Takahashi
- Akita Prefectural Livestock Experiment Station, Daisen 019-1701, Japan
| | - Kazuhiro Rikimaru
- Akita Prefectural Livestock Experiment Station, Daisen 019-1701, Japan
| | - Megumi Komatsu
- Akita Prefectural Livestock Experiment Station, Daisen 019-1701, Japan
| | - Yoshinobu Uemoto
- National Livestock Breeding Center, Nishigo, Fukushima 961-8511, Japan
| | - Keiichi Suzuki
- Graduate School of Agricultural Science, Tohoku University, Sendai 981-8555, Japan
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Miegueu P, Cianflone K, Richard D, St-Pierre DH. Motilin stimulates preadipocyte proliferation and differentiation and adipocyte lipid storage. Am J Physiol Endocrinol Metab 2011; 301:E758-66. [PMID: 21771971 DOI: 10.1152/ajpendo.00089.2011] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Motilin is a circulating gastrointestinal peptide secreted primarily by duodenal mucosal M cells and recognized for its prokinetic effects on gastrointestinal tissues. Little information is available regarding effects on insulin/glucose homeostasis or adipocyte function. Our aim was to evaluate the effects of motilin on adipocyte proliferation, differentiation, lipolysis, and macronutrient uptake in adipocytes. 3T3-L1 cells and primary rat adipocytes were treated acutely and chronically with varying motilin concentrations, and effects were compared with vehicle alone (control), set as 100% for all assays. In preadipocytes, motilin stimulated proliferation ([(3)H]thymidine incorporation) and mitochondrial activity (141 ± 10%, P < 0.001 and 158 ± 10%, respectively, P < 0.001), in a concentration-dependent manner. Chronic supplementation with motilin during differentiation further increased lipogenesis (Oil red O staining 191 ± 27%, P < 0.05) and was associated with an upregulation of PPARγ (148 ± 8%, P < 0.01), C/EBPα (142 ± 17%, P < 0.05), and Cav3 (166 ± 20%, P < 0.05) expression. In mature 3T3-L1 adipocytes motilin increased fatty acid uptake/incorporation (≤ 202 ± 12%; P < 0.01) and glucose uptake (146 ± 9% P < 0.05) and decreased net fatty acid release (maximal -31%, P < 0.05) without influencing total lipolysis (glycerol release). Similar effects were obtained in primary rat adipocytes. Motilin acutely increased expression of PPARγ, CEBPβ, DGAT1, and CD36 while decreasing adiponectin mRNA and secretion. In human adipose tissue, motilin receptor GPR38 correlated with HOMA-IR and GHSR1 (r = 0.876, P < 0.0001). Motilin binding and fatty acid incorporation into adipocytes were inhibited by antagonists MB10 and [D-lys3]-GRP6 and PI 3-kinase inhibitor wortmannin. Taken together, these results suggest that motilin may directly influence adipocyte functions by stimulating energy storage.
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Affiliation(s)
- Pierre Miegueu
- Institut Universitaire de Cardiologie et de Pneumologie de Québec, Quebec, Canada
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Taka N, Matsuoka H, Sato T, Yoshino H, Imaoka I, Sato H, Kotake KI, Kumagai Y, Kamei K, Ozaki KI, Higashida A, Kuroki T. Discovery of novel motilin antagonists: Conversion of tetrapeptide leads to orally available peptidomimetics. Bioorg Med Chem Lett 2009; 19:3426-9. [DOI: 10.1016/j.bmcl.2009.05.059] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2008] [Revised: 05/07/2009] [Accepted: 05/11/2009] [Indexed: 01/14/2023]
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Yamamoto I, Kaiya H, Tsutsui C, Sakai T, Tsukada A, Miyazato M, Tanaka M. Primary structure, tissue distribution, and biological activity of chicken motilin receptor. Gen Comp Endocrinol 2008; 156:509-14. [PMID: 18433751 DOI: 10.1016/j.ygcen.2008.03.007] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/01/2007] [Revised: 03/10/2008] [Accepted: 03/11/2008] [Indexed: 10/22/2022]
Abstract
Motilin is a peptide hormone involved in gastrointestinal motility. GPR38, initially cloned as an orphan receptor, is now considered a specific receptor for motilin. Previously, molecular characterization of the motilin receptor had only been performed in mammalian and fish species. In this study, we cloned cDNA for chicken motilin receptor from the duodenum and characterized its primary structure, tissue distribution, and biological activity. The cDNA encoded 349 amino acids showing significant overall sequence identity to mammalian motilin receptors. Chicken motilin increased intracellular Ca2+ concentration in human embryonic kidney (HEK) 293 cells transiently expressing the recombinant chicken motilin receptor. Comparison of the cDNA sequence with the genomic sequence of chicken motilin receptor revealed that the chicken motilin receptor gene consists of two exons separated by an intron. Real-time PCR analysis showed that chicken motilin receptor mRNA is expressed in a wide range of tissues in 21-day-old chickens, with markedly high levels in the proventriculus, duodenum, and oviduct. The expression levels of the mRNA in the proventriculus and duodenum were highest just before hatching and rapidly decreased during post-hatch development. These results suggest that chicken motilin receptor is largely involved in gastrointestinal functions at pre- and post-hatch periods through an intracellular signaling pathway accompanied by an increase in Ca2+ levels.
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Affiliation(s)
- Ichiro Yamamoto
- High-Tech Research Center, Nippon Veterinary and Life Science University, Musashino, Tokyo 180-8602, Japan
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Oral administration of MA-2029, a novel selective and competitive motilin receptor antagonist, inhibits motilin-induced intestinal contractions and visceral pain in rabbits. Eur J Pharmacol 2008; 581:296-305. [DOI: 10.1016/j.ejphar.2007.11.049] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2007] [Revised: 11/20/2007] [Accepted: 11/21/2007] [Indexed: 12/30/2022]
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Matsuura B, Dong M, Coulie B, Pinon DI, Miller LJ. Demonstration of a Specific Site of Covalent Labeling of the Human Motilin Receptor Using a Biologically Active Photolabile Motilin Analog. J Pharmacol Exp Ther 2005; 313:1101-8. [PMID: 15677347 DOI: 10.1124/jpet.104.081562] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The motilin receptor belongs to a group of class I G protein-coupled receptors that also includes the growth hormone secretagogue and ghrelin receptors. These represent clinically useful targets for pharmacotherapy. Their potentially unique structures and the molecular basis of their binding are not yet clear. We previously reported the initial affinity labeling of a region within this receptor (a cyanogen bromide fragment extending from the first to the second extracellular loop) using a position 1 photolabile motilin analog. To extend our understanding of the molecular basis of motilin binding, we have developed an additional radioiodinatable motilin analog probe having site of covalent attachment in position 5. This was a full agonist that bound to the motilin receptor specifically and with high affinity, and that efficiently established a single covalent bond to its receptor. Sequential chemical and enzymatic cleavage of labeled wild-type and mutant motilin receptor constructs established that the region of labeling was within the third extracellular loop. This was further localized to Phe(332) using radiochemical Edman degradation sequencing. These data provide the first spatial approximation constraint that can be used in the docking of this peptide ligand to its receptor. We hope that a series of such constraints can be determined to provide adequate structural information to begin to elucidate the conformation of this agonist-bound receptor and to ultimately be useful in the rational design of drugs acting at this important target.
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Affiliation(s)
- Bunzo Matsuura
- Cancer Center and Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic in Scottsdale, AZ 85259, USA
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Kamerling IMC, van Haarst AD, Burggraaf J, Schoemaker RC, de Kam ML, Heinzerling H, Cohen AF, Masclee AAM. Effects of a nonpeptide motilin receptor antagonist on proximal gastric motor function. Br J Clin Pharmacol 2004; 57:393-401. [PMID: 15025736 PMCID: PMC1884467 DOI: 10.1046/j.1365-2125.2003.02034.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
AIM To assess the effects of the motilin receptor antagonist RWJ-68023 on basal and motilin-stimulated proximal gastric volume. METHODS Eighteen healthy male volunteers received RWJ-68023 in two different doses or placebo for 135 min. After 45 min, subjects received a motilin infusion for 90 min. Proximal gastric volume was measured with a barostat at constant pressure and during isobaric distensions. Abdominal symptoms were scored using visual analogue scales. Motilin and RWJ-68023 concentrations were assessed by radioimmunoassay and liquid chromatography-mass spectrometry, respectively. RESULTS Both dosages of RWJ-68023 were safe and well tolerated. The most common adverse events were of gastrointestinal origin. RWJ-68023 did not affect basal proximal gastric volume, but the high-dose RWJ-68023 reduced the contractile effect of motilin on the stomach. This antagonizing effect of RWJ-68023 was only significant (P = 0.014) during the distension procedure. CONCLUSIONS The RWJ-68023 doses used in this study were selected to accomplish plasma concentrations that would block the motilin effect entirely. However, the antagonizing effect of RWJ-68023 was partial and only present when the tonic condition of the stomach was modulated by motilin.
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Coulie B, Matsuura B, Dong M, Hadac EM, Pinon DI, Feighner SD, Howard AD, Miller LJ. Identification of peptide ligand-binding domains within the human motilin receptor using photoaffinity labeling. J Biol Chem 2001; 276:35518-22. [PMID: 11461914 DOI: 10.1074/jbc.m104489200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cDNA encoding the human motilin receptor was recently cloned and found to represent a G protein-coupled receptor that is structurally related to the growth hormone secretagogue receptors. Together, these represent a new Class I receptor family. Our aim in the present work is to gain insight into the molecular basis of binding of motilin to its receptor using photoaffinity labeling. To achieve this, we developed a Chinese hamster ovary cell line that overexpressed functional motilin receptor (CHO-MtlR; 175,000 sites per cell, with K(i) = 2.3 +/- 0.4 nm motilin and EC(50) = 0.3 +/- 0.1 nm motilin) and a radioiodinatable peptide analogue of human motilin that incorporated a photolabile p-benzoyl-l-phenylalanine (Bpa) residue into its pharmacophoric domain. This probe, [Bpa(1),Ile(13)]motilin, was a full agonist at the motilin receptor that increased intracellular calcium in a concentration-dependent manner (EC(50) = 1.5 +/- 0.4 nm). This photolabile ligand bound specifically and with high affinity to the motilin receptor (K(i) = 12.4 +/- 1.0 nm), and covalently labeled that molecule within its M(r) = 45,000 deglycosylated core. Cyanogen bromide cleavage demonstrated its covalent attachment to fragments of the receptor having apparent M(r) = 6,000 and M(r) = 31,000. These were demonstrated to represent fragments that included both the first and the large second extracellular loop domains, with the latter representing a unique structural feature of this receptor. The spatial approximation of the pharmacophoric domain of motilin with these receptor domains support their functional importance as well.
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Affiliation(s)
- B Coulie
- Center for Basic Research in Digestive Diseases, Departments of Internal Medicine and Biochemistry/Molecular Biology, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA
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Haramura M, Okamachi A, Tsuzuki K, Yogo K, Ikuta M, Kozono T, Takanashi H, Murayama E. Design and synthesis of N-terminal cyclic motilin partial peptides: a novel pure motilin antagonist. Chem Pharm Bull (Tokyo) 2001; 49:40-3. [PMID: 11201222 DOI: 10.1248/cpb.49.40] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Motilin antagonist was designed and synthesized on the basis of the structure-activity relationship analysis of porcine motilin that we reported recently. The drug design was performed on a specific concept to reduce a flexibility of peptide conformation of porcine motilin partial peptide by its cyclization. The cyclic peptide was synthesized using Boc (tert-butyloxycarbonyl) solid phase methodology, followed by cyclization using the azide procedure, and tested for the binding activity to motilin receptor and smooth muscle contractile activity. The cyclic peptides 3, 4, and 5 showed antagonistic property on contraction assay (pA2 [the negative logarithm of molar concentration of antagonist causing a 2-hold shift to the right of the concentration-response curve for motilin]: 4.5, 4.34, and 4.04, respectively, in rabbit duodenum) and no contractile activity even at high concentration.
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Affiliation(s)
- M Haramura
- Fuji-Gotemba Research Laboratories, Chugai Pharmaceutical Co. Ltd., Shizuoka, Japan.
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Abstract
Motilin receptors were classically recognized in the gastroduodenal area, where they help to regulate interdigestive motility. More recently, motilin receptors were identified in the colon where their biologic significance remains unclear. We aimed here to characterize the motilin receptors of the rabbit colon. Distal colon and duodenum were obtained from sacrificed rabbits. Tissues homogenized by Polytron were submitted to differential centrifugation to obtain neural synaptosomes or smooth muscle plasma membranes enriched solutions. Motilin binding to these membranes was determined by the displacement of (125)I MOT by the native peptide MOT 1-22, or by peptide analogues MOT 1-12 [CH(2)NH](10-11) or GM-109 and by erythromycin derivative GM-611. Motilin binding capacity was maximum in colon nerves (49.5 +/- 6.5 fmol/mg protein vs. 19.9 +/- 2.5 in colon muscles or 9.4 +/- 2.8 and 6.6 +/- 1.2 in duodenal muscles and antral nerves respectively); all tissues expressed similar affinity for MOT 1-22, and the motilin agonist GM-611 bound equally to neural or muscle tissues from the rabbit colon; the synthetic antagonist MOT 1-12 [CH(2)NH](10-11) showed greater affinity for colon nerves than for colon muscles (plC50: 7.23 +/- 0.07 vs. 6.75 +/- 0.03). Similar results were obtained with the peptide antagonist GM-109; receptor affinity toward MOT 1-12 [CH(2)NH(10-11)] was always five times superior in neural tissues, whether they came from the colon or the antrum, than in muscle tissues, whether they were obtained from colon or from duodenum. Motilin receptors are found in very high concentration in nerves and in muscles from rabbit colon; specific motilin receptor subtypes are identified in nerves (N) and muscles (M) of the rabbit colon; N and M receptor subtypes seem independent of the organ location.
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Affiliation(s)
- P Miller
- Centre Hospitalier de l'Université de Montréal, Hôpital Saint-Luc, Centre de Recherche, 264 Blvd. Rene-Levesque Est, Montréal, Quebec, Canada
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Miller P, Roy A, St-Pierre S, Dagenais M, Lapointe R, Poitras P. Motilin receptors in the human antrum. Am J Physiol Gastrointest Liver Physiol 2000; 278:G18-23. [PMID: 10644557 DOI: 10.1152/ajpgi.2000.278.1.g18] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Motilin is an intestinal peptide that stimulates contraction of gut smooth muscle. The motilin receptor has not been cloned yet, but motilin-receptor agonists appear to be potent prokinetic agents for the treatment of dysmotility disorders. The aim of this study was to determine neural or muscular localization of motilin receptors in human upper gastrointestinal tract and to investigate their pharmacological characteristics. The binding of (125)I-labeled motilin to tissue membranes prepared from human stomach and duodenum was studied; rabbit tissues were used for comparison. Solutions enriched in neural synaptosomes or in smooth muscle plasma membranes were obtained. Various motilin analogs were used to displace the motilin radioligand from the various tissue membranes. The highest concentration of human motilin receptors was found in the antrum, predominantly in the neural preparation. Human motilin receptors were sensitive to the NH(2)-terminal portion of the motilin molecule, but comparison with rabbit showed that both species had specific affinities for various motilin analogs [i.e., Mot-(1-9), Mot-(1-12), Mot-(1-12) (CH(2)NH)(10-11), and erythromycin]. Motilin receptors obtained from synaptosomes or muscular plasma membranes of human antrum expressed different affinity for two motilin-receptor agonists, Mot-(1-12) and Mot-(1-12) (CH(2)NH)(10-11), suggesting that they correspond to specific receptor subtypes. We conclude that human motilin receptors are located predominantly in nerves of the antral wall, are functionally (and probably structurally) different from those found in other species such as the rabbit, and express specific functional (and probably structural) characteristics dependent on their localization on antral nerves or muscles, suggesting the existence of specific receptor subtypes, potentially of significant physiological or pharmacological relevance.
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Affiliation(s)
- P Miller
- Gastrointestinal Unit, Centre Hospitalier de l'Université de Montréal, Montreal, Quebec, Canada H2X 3J4
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Poitras P, Miller P, Dickner M, Mao YK, Daniel EE, St-Pierre S, Trudel L. Heterogeneity of motilin receptors in the gastrointestinal tract of the rabbit. Peptides 1996; 17:701-7. [PMID: 8804083 DOI: 10.1016/0196-9781(96)00053-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Motilin, a 22-amino acid peptide synthesized in endocrine cells of intestinal mucosa, stimulates GI smooth muscle contractility. To elucidate the mode of action of motilin, we attempted to determine whether motilin receptors are localized on nerve cells or on smooth muscle cells of the GI tract. Mucosa-free tissues from rabbit antrum and duodenum were homogenized separately with a Polytron prior to differential centrifugation to obtain synaptosome or plasma membrane-enriched fractions, as determined by the distribution of [3H]saxitoxin (SAX) binding (neural membranes) and 5' nucleotidase (5'N) activity (smooth muscle plasma membranes). Motilin binding was evaluated by the displacement of [125I]motilin by motilin (1-22) on the various membrane fractions. In the antrum, motilin binding was highly correlated with SAX binding (r = 0.81, p < 0.0005), and also significantly with 5'N activity (r = 0.54, p < 0.05). In the duodenum, motilin binding correlated significantly with 5'N activity (r = 0.67, p < 0.005), but not with SAX binding (r = -0.11, NS). Receptor affinity, for the motilin antagonist MOT(1-12)[CH2NH]10-11, for motilin(1-22), and for the motilin agonist erythromycin lactobionate was significantly (p < 0.001, p < 0.001, and p < 0.05, respectively) higher in SAX-enriched fractions from the antrum than in 5'N-enriched fractions from the duodenum. Therefore, in the rabbit: 1) motilin receptors appear to be predominantly located on nerve tissues in the antrum and restricted to smooth muscle cells in the duodenum, and 2) antral receptors and duodenal receptors displayed different pharmacological characteristics, probably corresponding to two specific and heterogeneous motilin receptor subtypes.
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Affiliation(s)
- P Poitras
- Centre de recherche clinique André-Viallet, Hôpital Saint-Luc, Université de Montréal, Québec, Canada
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