Partial agonist clonidine mediates alpha(2)-AR subtypes specific regulation of cAMP accumulation in adenylyl cyclase II transfected DDT1-MF2 cells.
alpha2-Adrenergic receptor (alpha(2)-AR) activation in the pregnant rat myometrium at midterm potentiates beta(2)-AR stimulation of adenylyl cyclase (AC) via Gbetagamma regulation of the type II isoform of adenylyl cyclase. However, at term, alpha(2)-AR activation inhibits beta(2)-AR stimulation of AC. This phenomenon is associated with changes in alpha(2)-AR subtype expression (midterm alpha(2A/D)-AR >> alpha(2B)-AR; term alpha(2B) >or =alpha(2A/D)-AR), without any change in ACII mRNA, suggesting that alpha(2A/D)- and alpha(2B)-AR differentially regulate beta(2)-cAMP production. To address this issue, we have stably expressed the same density of alpha(2A/D)- or alpha(2B)-AR with AC II in DDT1-MF2 cells. Clonidine (partial agonist) increased beta(2)-AR-stimulated cAMP production in alpha(2A/D)-AR-ACII transfectants but inhibited it in alpha(2B)-AR-ACII transfectants. In contrast, epinephrine (full agonist) enhanced beta(2)-stimulated ACII in both alpha(2A)- and alpha(2B)-ACII clonal cell lines. 4-Azidoanilido-[alpha-(32)P]GTP-labeling of activated G proteins indicated that, in alpha(2B)-AR transfectants, clonidine activated only Gi(2), whereas epinephrine, the full agonist, effectively coupled to Gi(2) and Gi(3). Thus, partial and full agonists selectively activate G proteins that lead to drug specific effects on effectors. Moreover, these data indicate that Gi(3) activation is required for potentiation of beta(2)-AR stimulation of AC by alpha(2A/D) and alpha(2B)-AR in DDT1-MF2 cells. This may reflect an issue of the amount of Gbetagamma released upon receptor activation and/or betagamma composition of Gi(3) versus Gi(2).
Limon-Boulez
I
I
Laboratoire de Physiologie de la Reproduction, Centre National de la Recherche Scientifique ESA 7080, Université Pierre et Marie Curie, Paris, France. isabelle.limon-boulez@snv.jussieu.fr
Bouet-Alard
R
R
Gettys
T W
TW
Lanier
S M
SM
Maltier
J P
JP
Legrand
C
C
D000262:Adenylyl Cyclases / Q000235:genetics / Q000378:metabolism*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D003000:Clonidine / Q000494:pharmacology*; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism*; D004837:Epinephrine / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D011233:Precipitin Tests; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured
C547773:Adra2b protein, rat; D000316:Adrenergic alpha-Agonists; D018341:Receptors, Adrenergic, alpha-2; D000242:Cyclic AMP; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D000262:Adenylyl Cyclases; C100622:adenylyl cyclase 2; D003000:Clonidine; D004837:Epinephrine