Coupling of human α2-adrenoceptor subtypes to regulation of cAMP production in transfected S115 cells

• Published in: European journal of pharmacology. Molecular pharmacology section Vol. 266; no. 2; pp. 165 - 174
• Main Authors: Jansson, Christian C., Marjamäki, Anne, Luomala, Kirsti, Savola, Juha-Matti, Scheinin, Mika, Åkerman, Karl E.O.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 1994; Elsevier
• Subjects: [ 3H]Rauwolscine; Adenosinic and purinergic receptors; Biological and medical sciences; cAMP; Cell receptors; Cell structures and functions; Fundamental and applied biological sciences. Psychology; Ligand binding; Molecular and cellular biology; Signal transduction; α2-Adrenoceptor subtype; α 2-Adrenoceptor subtype; Ligand binding; Signal transduction; [ 3H]Rauwolscine; cAMP; α2-Adrenergic receptor; Cell culture; Agonist; Rodentia; Cyclic AMP; Malignant tumor; In vitro; Vertebrata; Regulation(control); Mammalia; Mouse; Female genital system; Mammary gland; G protein
• ISSN: 0922-4106
• DOI: 10.1016/0922-4106(94)90106-6

Stable S115 mouse mammary tumour cell lines, expressing separately α 2A-C10, α 2B-C2 and α 2C-C4 adrenoceptors were used to compare the receptor binding properties of α 2-adrenoceptor agonists with their potency in inhibiting cAMP production. All tested agonists detected high and low affinity binding sites in all three receptor subtypes. In the presence of the GTP analogue Gpp(NH)p (10 μM), all displacement curves were shifted to the right and were best modelled by one-site fits, suggesting that the receptor subtypes are coupled to G-proteins. The extent of the Gpp(NH)p-induced shift was greatest in the α 2A-C10 subtype, smaller in α 2C-C4, and minimal in α 2B-C2. All three receptor subtypes were also coupled to inhibition of forskolin-stimulated cAMP production through pertussis toxin-sensitive G-proteins. For the the full agonists noradrenaline, UK 14,304, and dexmedetomidine, the maximal inhibitory effect on cAMP production was smaller in the α 2B-C2 subtype (35%) than in the α 2A-C10 and α 2C-C4 subtypes (50–70%). After treatment of cells expressing α 2B-C2 receptors with pertussis toxin, cAMP production was increased by up to 58% by α 2-adrenoceptor agonists. Similar stimulation of adenylyl cyclase activity could not be demonstrated at the other two receptor subtypes. In conclusion, these results demonstrate that (1) α 2-adrenoceptor agonists may be characterized by an agonist-type binding pattern in homogenates of transfected S115 cells, (2) all three α 2-adrenoceptor subtypes are coupled to inhibition of adenylyl cyclase in S115 cells through pertussis toxin-sensitive G-proteins (3) the receptor-effector coupling in S115 cells is different among the subtypes so that the α 2A-C10 subtype is coupled with high efficacy but with low sensitivity, the α 2B-C2 subtype with low efficacy but high sensitivity, and the α 2C-C4 subtype with both high efficacy and high sensitivity, and (4) at least α 2B-C2 receptors may also be coupled to stimulation of adenylyl cyclase activity, presumably through G s.