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

doi:10.1016/0922-4106(94)90106-6

European Journal of Pharmacology: Molecular Pharmacology

Volume 266, Issue 2, 15 January 1994, Pages 165-174

https://doi.org/10.1016/0922-4106(94)90106-6 Get rights and content

Abstract

Stable S115 mouse mammary tumour cell lines, expressing separately α₂A-C10, α₂B-C2 and α₂C-C4 adrenoceptors were used to compare the receptor binding properties of α₂-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 α₂A-C10 subtype, smaller in α₂C-C4, and minimal in α₂B-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 α₂B-C2 subtype (35%) than in the α₂A-C10 and α₂C-C4 subtypes (50–70%). After treatment of cells expressing α₂B-C2 receptors with pertussis toxin, cAMP production was increased by up to 58% by α₂-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) α₂-adrenoceptor agonists may be characterized by an agonist-type binding pattern in homogenates of transfected S115 cells, (2) all three α₂-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 α₂A-C10 subtype is coupled with high efficacy but with low sensitivity, the α₂B-C2 subtype with low efficacy but high sensitivity, and the α₂C-C4 subtype with both high efficacy and high sensitivity, and (4) at least α₂B-C2 receptors may also be coupled to stimulation of adenylyl cyclase activity, presumably through G_s.

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

Abstract

Trends Pharmacol. Sci.

Anal. Biochem.

Biochim. Biophys. Acta

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