β-Adrenoceptors belong to the large family of receptors coupled to GTP-binding proteins. Three β-adrenoceptor subtypes have been identified as follows: β1-, β2- and β3-adrenoceptor. This review shows the characteristics and its signal transduction pathways of β3-adrenoceptor-mediated relaxations in guinea pig gastric fundus smooth muscle. The relaxations in response to the stimulation of β-adrenoceptor with (-)-isoprenaline are involved in β3-adrenoceptors as well as β1-adrenoceptors. The study of determination of stereochemical specificity for β3-adrenoceptors suggests that (-)-enantiomers are more potent than its (+)-enantiomers and that the stereoselectivity of β3-adrenoceptors is lower than that of β1- and β2-adrenoceptors. The functional data on signal transduction mechanisms discloses that the stimulation of β3-adrenoceptor induces both cyclic AMP-dependent and cyclic AMP-independent
relaxant responses. 4-Aminopyridine-sensitive voltage-gated K+ (Kv) channels play a primary role in the cyclic AMP-independent relaxations of guinea pig gastric fundus in response to the stimulation of β3-adrenoceptors.
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