The beta2-adrenergic receptor specifically sequesters Gs but signals through both Gs and Gi/o in rat sympathetic neurons.
Beta(2)-adrenergic receptors (beta(2)-AR) and CB1 cannabinoid receptors share the property of being constitutively active. The CB1 cannabinoid receptor can also sequester G(i/o) proteins; however, it is not known whether the beta(2)-AR can also sequester G proteins. Beta(2)-ARs were heterologously expressed in rat superior cervical ganglion neurons by microinjection of cDNA and studied using the patch-clamp technique. The beta-AR agonist isoproterenol increased the Ca(2+) current 25.9+/-1.6% in neurons microinjected with 100 ng/microl beta(2)-AR cDNA but was without effect on control neurons. Pretreatment with cholera toxin (CTX) abolished the effect of isoproterenol, indicating coupling via G(s) proteins. In neurons microinjected with 200 ng/microl beta(2)-AR cDNA, isoproterenol had the opposite effect of inhibiting the Ca(2+) current 36.5+/-2.0%. Inhibition of the Ca(2+) current was sensitive to pertussis toxin, indicating beta(2)-AR coupling to G(i/o) proteins. Pretreatment with CTX resulted in a greater 54+/-3.8% inhibition of the Ca(2+) current, indicating that G(s) coupling masks the full effect of G(i/o) coupling. Expression of beta(2)-ARs abolished signaling by G(s)-coupled receptors for vasoactive intestinal polypeptide (VIP). VIP inhibited the Ca(2+) current 49.5+/-0.5% in control neurons but had no effect in neurons expressing beta(2)-ARs. In contrast, expression of beta(2)-ARs had no effect on signaling by the G(i/o)-coupled alpha(2)-adrenergic receptor. This study demonstrates that the beta(2)-AR couples to both G(s) and G(i/o) proteins but specifically sequesters G(s) proteins, preventing their interaction with another G(s)-coupled receptor. beta(2)-adrenergic receptors thus have the potential to prevent other G(s)-coupled receptors from transducing their biological signals.
Vásquez
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Department of Pharmacology and Toxicology, Medical College of Georgia, 1120 15th Street, Augusta, GA 30912-2300, USA.
Lewis
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D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology; D018076:DNA, Complementary; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000187:drug effects / Q000378:metabolism*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000187:drug effects / Q000378:metabolism*; D020962:Heterotrimeric GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018343:Receptors, Adrenergic, beta-2 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D017783:Superior Cervical Ganglion / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D000318:Adrenergic beta-Agonists; D018076:DNA, Complementary; D018343:Receptors, Adrenergic, beta-2; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug; D014660:Vasoactive Intestinal Peptide; D002772:Cholera Toxin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D019205:GTP-Binding Protein alpha Subunits, Gs; D020962:Heterotrimeric GTP-Binding Proteins