The β-ARs are members of a large family of neurotransmitter receptors, which interact with GTP binding proteins (G-proteins) to modulate second messenger systems (1,2). The β-ARs mediate the physiological effects of the catecholamines epinephrine and norepinephrine; when ligand-activated, these receptors initiate the production of cyclic AMP. Three subtypes of β-ARs, β₁-AR, β₂-AR, and β₃-AR, have been identified on the basis of their pharmacological properties, physiological effects, tissue and cell-type specificity, and genetic structure (1–2). All three β-AR subtypes have conserved structural features, including hydrophobicity profiles consistent with seven-transmembrane domains, sites of N-linked glycosylation near the amino-terminus, potential phosphorylation sites for protein kinases in presumed cytoplasmic domains, and highly conserved amino acid similarity within the transmembrane domains.