DEVELOPMENTAL EXPRESSION AND FUNCTIONAL-ACTIVITY OF BETA(1)-ADRENOCEPTOR AND BETA(3)-ADRENOCEPTOR IN MURINE 3T3-F442A DIFFERENTIATING ADIPOCYTES

beta(1)- and beta(3)-adrenoceptor mRNA and protein expression, and con tribution of each subtype to the catecholamine-sensitive adenylyl cycl ase system were studied during the adipose conversion of the murine 3T 3-F442A cell line. Northern and reverse transcriptase-polymerase chain reaction analyses indicated that emergence of beta(3)-adrenoceptor tr anscripts was concomittant with that of the gene encoding adipsin, a v ery late marker of adipose differentiation. Conversely, the induction of the beta(1)-adrenoceptor mRNA occurred early after cell commitment towards adipose conversion. Changes in beta-subtype gene expression we re accompanied by parallel modifications in receptor expression and fu nction. I-125-cyanopindolol saturation and competition binding experim ents showed a 3-fold increase in beta(1)-adrenoceptor density in day 3 post-confluent cells. The beta(3)-subtype population became detectabl e later and represented similar to 95% of total beta-adrenoceptors in day 8 and day 12 post-confluent cells. Adenylyl cyclase activity in re sponse to the beta(3)-adrenoceptor-selective agonists CGP12177 -butyla mino-2-hydroxypropoxy)-benzimidazol-2-one), ICI201651 ([(R)-4-(2 mino- elhoxy)-N-(2-methoxyethyl)phenoxy-acetamide]) and cyanopindolol was vi rtually absent in young adipocytes, but dramatically increased in matu re cells. The respective contributions of the beta(1)- and the beta(3) -subtypes to the production of cAMP were resolved by an Eadie-Hofstee computer analysis of isoproterenol and norepinephrine concentration-re sponse curve of adenylyl cyclase activity. Agonist response curves in the presence of beta(1)- and beta(2)-adrenoceptor antagonists indicate d that the beta(1)-subtype accounted for the totality of beta-adrenoce ptor-mediated adenylyl cyclase activation in young adipocytes. In matu re adipose cells similar to 90% of this response was due to an activat ion of the beta(3)-adrenoceptor. In addition, similar to 84% of the ma ximal norepinephrine-stimulated lipolysis was mediated by the beta(3)- adrenoceptor in fully differentiated adipocytes. The differentiation-d ependent expression of P-subtypes in adipocytes is a biphasic process involving an initial and moderate induction of beta(1)-adrenoceptors f ollowed by the emergence of a prominent beta(3)-adrenoceptor populatio n. Compared analysis of both receptor occupancy and cAMP production sh ows that the beta(3)-subtype is more efficiently coupled to the adenyl yl cyclase system than the beta(1)-adrenoceptor. Thus in mature adipos e cells this receptor subtype represents the core of cAMP-dependent re gulation of the lipolytic, antilipogenic and thermogenic effects of ca techolamines.