[Characterization of muscarinic receptors in undifferentiated thyroid cells in Fisher rats]. / Caracterización de receptores muscarínicos en células indiferenciadas tiroideas de ratas Fisher.

INTRODUCTION: The parasympathetic autonomous nervous system exerts control over thyroid function by activation of the muscarinic receptors in follicular cells. Various pharmacological and molecular subtypes of muscarinic receptors (M(1), M(2), M(3), M(4), M(5)) have been identified in central nervous system and peripheral tissues. Controversy surrounds receptor characterization in thyroid cells. MATERIALS AND METHODS: Undifferentiated Fisher rat thyroid epithelial cells (FRT) were cultured. Association and dissociation kinetics assays and antagonist competition studies of the binding of (3)H-N-methylscopolamine ((3)H-NMS) to muscarinic receptors were performed to demonstrate the presence of muscarinic receptors. RESULTS: Specific muscarinic receptors in the plasma membrane of FRT cells were observed with an equilibrium dissociation constant (K(d)) of 0.44 nmol. The order of affinities obtained fitting the data to one binding site model in competition experiments with the muscarinic receptor antagonist was: dicyclomine > hexahydrosiladifenidol (HHSD) = 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) > pirenzepine > himbacine = 11-[[2-[(diethylamino)methyl]- 1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido (414)benzodiazepine (AF-DX 116). CONCLUSIONS: The results obtained indicate the existence of specific (3)H-NMS muscarinic binding sites located in the plasma membrane of FRT cells. The results obtained in competition experiments suggest that the receptors present in FRT cells belong to the M(3) subtype.

Caracterización de receptores muscarínicos en células indiferenciadas tiroideas de ratas Fisher / Characterization of undifferentiated muscarinic thyroid cells in fisher rats

Introducción: El sistema nervioso autónomo parasimpático tiene el control de la función tiroidea mediante la activación de receptores muscarínicos en las células foliculares. Se han identificado diversos subtipos farmacológicos y moleculares de receptores muscarínicos (M1, M2, M3, M4, M5) tanto en el sistema nervioso central (SNC) como en los tejidos periféricos, pero hay controversia acerca de su caracterización en las células tiroideas. Material y métodos: Cultivos celulares de células epiteliales tiroideas indiferenciadas de ratas Fisher (FRT). Estudios de unión de receptores a radioligando: cinéticas de asociación, cinéticas de disociación y competiciones entre diversos fármacos antagonistas selectivos muscarínicos; se utiliza, como radioligando, 3H-N-metil-escopolamina (3H-NMS). Resultados: Se observa que hay receptores específicos muscarínicos en la membrana plasmática de las células FRT con una constante de disociación en equilibrio (Kd) de 0,44 nmol. El orden de afinidades de los diferentes antagonistas muscarínicos encontrado en membranas epiteliales de células FRT mediante el ajuste de los datos para un modelo de un solo sitio de unión fue: diciclomina > hexahidrosiladifenidol (HHSD) = 4-difenilacetoxi-N-metilpiperidina metiodida (4-DAMP) > pirenzepina > himbacina = 11-[[2-[(dietil-amino)metil]-1-piperidinil]acetil]-5,11-dihidro-6H-pirido(414)benzodiacepina (AF-DX 116).Conclusiones: Los resultados obtenidos en este estudio indican que hay sitios de unión para 3H-NMS que se corresponden con los receptores muscarínicos localizados en células FRT. Los resultados obtenidos en los experimentos de competición indican que el receptor presente en esta localización se corresponde con el subtipo M3 (AU)

Introduction: The parasympathetic autonomous nervous system exerts control over thyroid function by activation of the muscarinic receptors in follicular cells. Various pharmacological and molecular subtypes of muscarinic receptors (M1, M2, M3, M4, M5) have been identified in central nervous system and peripheral tissues. Controversy surrounds receptor characterization in thyroid cells. Materials and methods: Undifferentiated Fisher rat thyroid epithelial cells (FRT) were cultured. Association and dissociation kinetics assays and antagonist competition studies of the binding of 3H-N-methylscopolamine (3H-NMS) to muscarinic receptors were performed to demonstrate the presence of muscarinic receptors. Results: Specific muscarinic receptors in the plasma membrane of FRT cells were observed with an equilibrium dissociation constant (Kd) of 0.44 nmol. The order of affinities obtained fitting the data to one binding site model in competition experiments with the muscarinic receptor antagonist was: dicyclomine > hexahydrosiladifenidol (HHSD) = 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) > pirenzepine > himbacine = 11-[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido(414)benzodiazepine (AF-DX 116). Conclusions: The results obtained indicate the existence of specific 3H-NMS muscarinic binding sites located in the plasma membrane of FRT cells. The results obtained in competition experiments suggest that the receptors present in FRT cells belong to the M3 subtype (AU)