The β 2-adrenergic receptor specifically sequesters g s but signals through both G s and G i/o in rat sympathetic neurons

Abstract

β 2-adrenergic receptors (β 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 β 2-AR can also sequester G proteins. β 2-ARs were heterologously expressed in rat superior cervical ganglion neurons by microinjection of cDNA and studied using the patch-clamp technique. The β-AR agonist isoproterenol increased the Ca 2+ current 25.9±1.6% in neurons microinjected with 100 ng/μl β 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/μl β 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 β 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 β 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 β 2-ARs. In contrast, expression of β 2-ARs had no effect on signaling by the G i/o-coupled α 2-adrenergic receptor. This study demonstrates that the β 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. β 2-adrenergic receptors thus have the potential to prevent other G s-coupled receptors from transducing their biological signals.