Functional expression of adrenergic and opioid receptors in Xenopus oocytes: interaction between alpha 2- and beta 2-adrenergic receptors.
We functionally expressed alpha 2-adrenergic, beta 2-adrenergic, and delta-opioid receptors in Xenopus laevis oocytes. We detected receptor function as changes in currents carried by adenosine 3',5'-cyclic monophosphate (cAMP)-regulated chloride channels provided by the cystic fibrosis transmembrane conductance regulator (CFTR) and recorded by two-electrode voltage clamp. Co-application of forskolin and isobutylmethylxanthine (IBMX) or IBMX alone produced currents with a reversal potential indicative of chloride ions only in oocytes previously injected with mRNA encoding CFTR. Isoproterenol produced concentration-dependent responses in oocytes injected with mRNA encoding beta 2-adrenergic receptors and CFTR, and co-administration of propranolol antagonized these responses. Similarly, the alpha 2-adrenergic agonist UK14304 increased IBMX-induced currents only in oocytes injected with mRNA encoding alpha 2-adrenergic receptors and CFTR, and idazoxan antagonized these enhancements. The delta-opioid agonist DADLE produced concentration-related, naloxone-reversible increases in IBMX- and forskolin-induced currents only in oocytes injected with mRNA encoding delta-opioid receptors and CFTR. In oocytes co-injected with alpha 2, beta 2, and CFTR mRNAs, isobolographic analysis revealed an additive interaction between alpha 2- and beta 2-adrenergic receptors. These studies establish the oocyte as a cell system for studying the interactions among cAMP-modulating G protein-coupled receptors and provide another example of alternative coupling of alpha 2-adrenergic and delta-opioid receptors to G proteins, possibly Gs proteins, other than Gi proteins.
Birnbaum
A K
AK
Department of Pharmacology, University of Minnesota, Minneapolis 55455.
Wotta
D R
DR
Law
P Y
PY
Wilcox
G L
GL
D000262:Adenylyl Cyclases; D000818:Animals; D000068438:Brimonidine Tartrate; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D003550:Cystic Fibrosis; D004305:Dose-Response Relationship, Drug; D007545:Isoproterenol / Q000494:pharmacology*; D008954:Models, Biological; D009270:Naloxone / Q000494:pharmacology*; D009865:Oocytes; D011433:Propranolol / Q000494:pharmacology*; D011810:Quinoxalines / Q000494:pharmacology; D012333:RNA, Messenger; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology*; D018343:Receptors, Adrenergic, beta-2 / Q000502:physiology*; D011957:Receptors, Opioid; D014982:Xenopus laevis
D011810:Quinoxalines; D012333:RNA, Messenger; D018341:Receptors, Adrenergic, alpha-2; D018343:Receptors, Adrenergic, beta-2; D011957:Receptors, Opioid; D009270:Naloxone; D000068438:Brimonidine Tartrate; D011433:Propranolol; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D007545:Isoproterenol