Identification of adenylate cyclase-coupled beta-adrenergic receptors in the developing mammalian palate |
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Authors: | M P Garbarino R M Greene |
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Affiliation: | Department of Anatomy, Daniel Baugh Institute, Thomas Jefferson University, Philadelphia, PA 19107 USA |
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Abstract: | A direct radioligand binding technique utilizing a beta-adrenergic antagonist [3H]Dihydroalprenolol [( 3H]DHA) was employed in the identification and characterization of fetal palatal beta-adrenergic receptors. [3H]DHA binding was saturable (Bmax 16 fmol/mg protein) with high affinity and an apparent equilibrium dissociation constant (KD) of 1.5 nM. Binding of [3H]DHA was displaced by the competitive beta-adrenergic antagonist propranolol in a concentration-dependent manner. Dissociation kinetic studies demonstrated almost complete reversibility of radioligand binding within 60 min. The functionality of these beta-adrenergic receptors was demonstrated by showing that fetal palatal mesenchymal cells responded to catecholamine agonists with dose-dependent accumulations of intracellular cAMP. This effect could be entirely blocked by the beta-antagonist, propranolol. The relative potency order of catecholamines in eliciting an elevation of cellular cAMP was characteristic of a beta 2-adrenergic receptor-mediated response: (-) isoproterenol greater than (-) epinephrine greater than (-) norepinephrine. In addition, this response was found to be stereospecific with (-) isoproterenol being significantly more potent than (+) isoproterenol. Both the [3H]DHA binding characteristics and the catecholamine sensitivity of fetal palatal tissue support the presence of adenylate cyclase-coupled beta-adrenergic receptors in the developing mammalian secondary palate. |
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