title: The rabbit motilin receptor: molecular characterisation and pharmacology.
abstract: Following identification of the human motilin receptor, we isolated the rabbit orthologue by PCR amplification and found this to be 85% identical to the open reading frame of the human receptor. The protein encoded was 84% identical to the human polypeptide. In HEK293T cells transfected with the rabbit receptor, motilin concentration-dependently increased intracellular calcium mobilisation (pEC50=9.25). After transfection with Go1alpha, motilin similarly stimulated [35S]GTPgammaS binding (pEC50=8.87). Using both systems, similar values were obtained with the human receptor, with rank-order potencies of motilin=[Nle13]-motilin>erythromycin; ghrelin was ineffective. In circular muscle preparations of rabbit gastric antrum, [Nle13]-motilin 0.1-30 nM concentration-dependently increased the amplitude of electrically-evoked, neuronally-mediated contractions (pEC50=8.3); higher concentrations increased the muscle tension (30-3000 nM). Both responses to [Nle13]-motilin faded rapidly during its continual presence. Rat or human ghrelin 0.01-10 microM were without activity. Erythromycin 30-3000 nM and 10 microM, respectively, increased neuronal activity and muscle tension in rabbit stomach. Unlike [Nle13]-motilin, the increase in neuronal activity did not fade during continual presence of submaximally-effective concentrations of erythromycin; some fade was observed at higher concentrations. We conclude that the pharmacology of the rabbit motilin receptor is similar to the human orthologue and, when expressed as a recombinant, comparable to the native receptor. However, in terms of their ability to increase neuronal activity in rabbit stomach, [Nle13]-motilin and erythromycin are distinguished by different response kinetics, reflecting different rates of ligand degradation and/or interaction with the receptor.
mesh_terms: D000818:Animals; D001483:Base Sequence / Q000235:genetics; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008969:Molecular Sequence Data; D009037:Motilin / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D011706:Pyloric Antrum / Q000187:drug effects / Q000378:metabolism; D011817:Rabbits; D011964:Receptors, Gastrointestinal Hormone / Q000819:agonists / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018013:Receptors, Neuropeptide / Q000819:agonists / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D011964:Receptors, Gastrointestinal Hormone; D018013:Receptors, Neuropeptide; C050802:motilin receptor; D009037:Motilin