Monovalent Anions Differentially Modulate Coupling of the β2-Adrenoceptor to Gsα Splice Variants
- Dr. Roland Seifert, Department of Pharmacology and Toxicology, The University of Kansas, 5064 Malott Hall, Lawrence, KS 66045. E-mail:rseifert{at}ukans.edu
Abstract
The β2-adrenoceptor (β2AR) fused to the long splice variant of Gsα(GsαL), but not the β2AR fused to the short splice variant of Gsα(GsαS) shows the hallmarks of high constitutive activity, i.e., strong activation of adenylyl cyclase (AC) by GTP and strong inhibition of AC by inverse agonist. These coupling differences are the result of differences in GDP affinity of Gsα splice variants. The aim of this study was to identify experimental variables that differentially affect β2AR coupling to GsαS and GsαL. NaCl substantially reduced agonist-independent AC activation by GTP and inverse agonist inhibition and enhanced agonist stimulation of AC in Sf9 insect cell membranes expressing the β2AR-GsαL fusion protein. Salts reduced inverse agonist inhibition and increased agonist stimulation of AC in the order of efficiency NaI ∼ KI > NaBr ∼ KBr > NaCl ∼ LiCl ∼ KCl ∼ RbCl ∼ CsCl ∼ choline chloride, indicating that monovalent anions determine salt effects. Salts inhibited guanosine 5′-O-(3-thiotriphosphate)-mediated AC activation by GsαL without β2AR in the order of efficiency NaI > NaBr > NaCl. NaCl enhanced the affinity of GsαL for GDP. Salts had much smaller effects on β2AR ligand regulation of AC in membranes expressing β2AR-GsαS than in membranes expressing β2AR-GsαL. These data are explained by a model in which anions increase the GDP affinity of GsαL more efficiently than the GDP affinity of GsαS, and, thereby, decrease the efficiency of the agonist-free β2AR and increase the efficiency of the agonist-occupied β2AR at promoting GDP dissociation from GsαL. Thus, monovalent anions differentially regulate β2AR-coupling to GsαS and GsαL.
Footnotes
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The J. R. & Inez Jay Biomedical Research Award, a New Faculty Award of The University of Kansas, and a grant of the Army Research Office (DAAD19-00-1-0069) to R. S. supported this project. Initial experiments for this project were carried out at the Howard Hughes Medical Institute, Stanford University, Beckman Center, Stanford, CA 94305.
- Abbreviations:
- β2AR
- β2-adrenoceptor
- GPCR
- G protein-coupled receptor
- Gs protein
- G protein activating adenylyl cyclase
- AC
- adenylyl cyclase
- Gα
- nonspecified G protein α-subunit
- GsαL
- long splice variant of the Gs protein Gsα
- GsαS
- short splice variant of the Gs protein Gsα
- β2AR-GsαL
- fusion protein containing the β2AR and the long splice variant of Gsα
- β2AR-GsαS
- fusion protein containing the β2AR and the short splice variant of Gsα
- Gi protein
- G protein inhibiting adenylyl cyclase
- Go protein
- G protein expressed at high levels in the brain and neuroendocrine cells
- DHA
- [3H]dihydroalprenolol
- ICI
- ICI 118,551 [erythro-d-1-(7-methylindan-4-yloxy)-3-isopropylaminobutan-2-ol]
- ISO
- (−)-isoproterenol
- ChoCl
- choline chloride
- GTPγS
- guanosine 5′-O-(3-thio)triphosphate
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- Received December 12, 2000.
- Accepted April 16, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
