Sodium regulation of agonist and antagonist binding to ?-adrenoceptors in intact and Ns-deficient membranes

Abstract

Agonist binding to various hormone receptors mediating adenylate cyclase inhibition is decreased by sodium ions. We studied the influence of Na+ on agonist and antagonist binding to beta-adrenoceptors in membrane preparations of guinea pig lung, S49 lymphoma wild-type cells (WT) and their Ns-deficient cyc- variants by measuring binding of the antagonist, [125I]iodocyanopindolol [( 125I]CYP). At 37 degrees C, sodium decreased the receptor affinity for the agonist, isoproterenol, in all three membrane preparations. In lung and WT membranes, Na+ steepened the shallow agonist competition curves in a manner similar to and synergistic with guanine nucleotides. When binding was performed at 4 degrees C, sodium regulation but not guanine nucleotide regulation of agonist binding was preserved. At the low temperature, [125I]CYP affinity was reduced, and sodium increased [125I]CYP binding in both Ns-containing and Ns-deficient membranes by increasing the antagonist affinity without significant change in total receptor number. Compared to Na+, Li+ and K+ were much less potent and efficient in decreasing agonist and increasing antagonist binding. Na+ and Mg2+ had opposite effects on agonist binding in the Ns-containing lung and WT membranes but not in the Ns-deficient cyc- membranes. The data indicate that sodium not only regulates binding of inhibitory hormone receptors but also agonist and antagonist binding to the adenylate cyclase stimulatory beta-adrenoceptor. The finding that sodium regulation of beta-adrenoceptor binding is also observed in the Ns (alpha s)-deficient cyc- membranes, furthermore, indicates that the target of sodium is not the alpha-subunit of Ns but possibly a component common to both types of receptor systems regulating adenylate cyclase activity.

The 2.1 Å Resolution Structure of Cyanopindolol-Bound β1-Adrenoceptor Identifies an Intramembrane Na+ Ion that Stabilises the Ligand-Free Receptor

“…In contrast, there were no indications in the literature that Na + ions had a similar effect on β 1 AR. However, data on β 2 AR suggested Na + ions may be important for activity [42], particularly when considered in conjunction with data on the β 2 AR mutants D79A 2.50 or D79N 2.50 that showed decreased affinity of agonist binding and reduced receptor-mediated activation of G proteins [43], [44]. We therefore measured the affinities of agonist binding to membrane-bound wild-type β 1 AR in the presence of either 0 mM, 150 mM or 1 M NaCl.…”

Defective venous beta-adrenergic response in borderline hypertensive subjects is corrected by a low sodium diet.

“…In vitro, increasing sodium concentration reduces beta adrenoceptor response (20,21). Further, intracellular sodium content may be higher in hypertensives (22), and is reduced with dietary sodium restriction (23).…”

Differential Sensitivity to Cations of the Melatonin Receptors in the Rat Area Postrema and Suprachiasmatic Nuclei

“…For example, binding of isoproterenol to @-adrenoceptors of S49 mouse lymphoma cells was similarly regulated by Na+ in membranes prepared from wildtype (i.e. a,-containing) and a,-deficient cyc-cells (Minuth and Jakobs, 1986). Moreover, studies on GH4CI pituitary cells have shown that Na+ inhibited thyrotropin-releasing hormone binding only in membranes but not in intact cells (Hinkle and Kinsella, 1984).…”