THE CHARACTERISTICS OF [³H]‐CLONIDINE BINDING TO ANα‐ADRENOCEPTOR IN MEMBRANES FROM GUINEA‐PIG KIDNEY

[³H]‐clonidine binds to membranes prepared from guinea‐pig kidney. At 25°C the binding is rapid and saturable. Scatchard analysis of the binding data showed that the K_d for [³H]‐clonidine binding in kidney membranes is 8.54 nM and the density of binding sites 12.5 pmol/g wet wt. tissue. Hill plots of the binding data showed that there were no cooperative site interactions associated with binding. [³H]‐clonidine binding could be displaced by drugs, the most potent being drugs with a high affinity for the α‐adrenoceptor. The neuroleptic drugs (+)‐butaclamol, ds‐clopenthixol and ds‐flupen‐thixol at high concentration also displaced [³H]‐clonidine binding. Drugs acting as agonists or antagonists of β‐adrenoceptors, histamine receptors, acetylcholine receptors as well as prostaglandins E₁ E₂, F_lα and F_2α, angiotensin II, arginine vasopressin, naloxone, nalorphine and pargyline had little effect on binding. It is likely that the binding site labelled by [³H]‐clonidine in guinea‐pig kidney membranes is an α‐adrenoceptor similar in some pharmacological aspects to an a₂‐adrenoceptor. 1979 British Pharmacological Society