K. Elhadri et al., DEVELOPMENTAL EXPRESSION AND FUNCTIONAL-ACTIVITY OF BETA(1)-ADRENOCEPTOR AND BETA(3)-ADRENOCEPTOR IN MURINE 3T3-F442A DIFFERENTIATING ADIPOCYTES, European journal of pharmacology, 297(1-2), 1996, pp. 107-119
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.