Caracterización de receptores muscarínicos en células indiferenciadas tiroideas de ratas Fisher

Abstract

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.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.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).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.