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