Interaction of Clonidine and Clonidine Analogues with α‐Adrenergic Receptors of Neuroblastoma × Glioma Hybrid Cells and Rat Brain: Comparison of Ligand Binding with Inhibition of Adenylate Cyclase

Daphne ATLAS*, Steven L. SABOL

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

29 Scopus citations

Abstract

Clonidine and several analogues of clonidine are shown to be useful probes for α2‐adrenergic receptors in a comparative study of ligand binding and inhibition of adenylate cyclase. The α‐adrenergic properties of a new potential probe, N‐(4‐hydroxyphenacetyl)‐4‐aminoclonidine hydrochloride, are described. [3H]Clonidine binds to α‐receptors of NG108‐15 neuroblastoma × glioma hybrid cell membranes with Kd values of 1.7 and 33 nM for putative high‐affinity and low‐affinity sites, respectively. p‐Aminoclonidine and hydroxyphenacetyl aminoclonidine displace [3H]clonidine from the high‐affinity sites with Kd values of 2.3 and 5.8 nM, respectively. Rat brain α2‐receptors also exhibit high affinity toward clonidine, p‐aminoclonidine, and hydroxyphenacetyl aminoclonidine, as determined by displacement of specifically bound [3H]clonidine. Clonidine, p‐aminoclonidine, and hydroxyphenacetylaminoclonidine elicit modest inhibition (up to 24%) of NG108‐15 adenylate cyclase by interaction with α2‐receptors (Kd,app 300, 50, and 130 nM, respectively); these compounds also partially reverse the inhibition elicited by (–)‐norepinephrine. Components of the adenylate cyclase assay mixture, particularly ATP, GTP, sodium ions, and a nucleoside‐triphosphate‐regenerating system, decrease the high‐affinity [3H)clonidine binding to NG108‐15 membranes; in the presence of these components, α‐receptors possess only low affinity (Kd 43 nM) for [3H]clonidine. These results are consistent with the concept that certain components required for the receptor‐mediated inhibition of adenylate cyclase convert α2‐receptors from a high‐affinity inactive state to a low‐affinity active state.

Original languageEnglish
Pages (from-to)521-529
Number of pages9
JournalEuropean Journal of Biochemistry
Volume113
Issue number3
DOIs
StatePublished - Jan 1981

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