Transient high‐affinity binding of agonists to α1‐adrenergic receptors of intact liver cells

FEBS Letters

Carter, Edward A.²  Lanier, Stephen M.¹  Homey, Charles J.¹  Graham, Robert M.¹  Schwarz, Kurt R.¹ 

[1] Cardiac Unit, Massachusetts General Hospital, Boston, MA 02114, U.S.A.;Shriner's Burns Institute, Boston, MA 02114, USA

关键词: α1-Adrenergic receptor;    Isolated hepatocyte;    Glycogenolysis;    Nonequilibrium binding;    Conformational change;    Receptor affinity state;   

DOI  :  10.1016/0014-5793(85)81243-6

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

At α₁-adrenergic receptors in isolated rat liver parenchymal cells, (−)-epinephrine is potent in eliciting a maximal increase in glycogenolysis (K _act = 24 nM). This contrasts with a 100-fold lower affinity for the agonist at α₁-adrenergic receptors of intact hepatocytes determined from equilibrium competition assays with the α₁-adrenergic antagonist [³H]prazosin. We demonstrate here that agonists bind to α₁-adrenergic receptors of intact liver cells initially with a markedly higher affinity than under equilibrium conditions. When incubations are performed for 15 s at 37°C, the affinity is more than 100-fold higher than that obtained in equilibrium (45 min) assays (IC₅₀ = 28 ± 3 vs 5300 + 400 nM for (−)-epinephrine and 32 ± 3 vs 6100 ± 500 nM for (−)-norepinephrine). When incubations are performed at 4°C (150 min), high-affinity binding similar to that obtained In short-term incubations can also be demonstrated. In contrast, antagonist compete with similar affinities in 15 s and 45 min assays, and their dissociation constants are not affected by changes in the incubation temperature. These results indicate that agonists bind to native α-adrenergic receptors transiently with high affinity. The conversion of receptors to a state of predominantly low affinity for agonists, which occurs rapidly and irreversibly with increasing incubation at 37°C, is inhibited at low incubation temperatures. It is suggested that the high-affinity configuration of the α₁-adrenergic receptor for agonists observed in nonequilibrium experiments or at reduced incubation temperatures represents the physiologically relevant state of the α₁-adrenergic receptor.

【 授权许可】

Unknown