The human β3-adrenergic receptor: relationship with atypical receptors

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Abstract
Atypical β-adrenergic receptors (βAR), different from β1 and β2ARs, have been suggested to modulate energy expenditure. We have characterized a gene coding for a third human βAR, β3AR, whose sequence is 402 amino acids long and is 50.7% and 45.5% homologous to that of the human β1 and β2AR, respectively. The KD of [125I]-iodocyanopindolol for β3AR is 10-fold higher than for β1 or β2AR. The receptor has an apparent molecular weight of 65 000. Agonists for the β3AR induce cyclic AMP accumulation. Among 11 β antagonists tested, only ICI118551 and CGP20712A, previously classified as, respectively, β1 and β2 selective, inhibit this effect. The β1 and β2 antagonists pindolol, Oxprenolol, and CGP12177 are agonists of the β3AR. The potency order of β agonists at β3 sites correlates with that for stimulation of lipolysis in rat fat tissues. Moreover, because β3AR mRNA was detected in rodent adipose tissues, liver, and muscle, we propose that the β3AR participates to the control by catecholamines of energy expenditure.