β-adrenergic receptor binding characteristics and responsiveness in cultured Wistar-Kyoto rat arterial smooth muscle cells

The tone of arterial blood vessels is regulated by the catecholamines through their receptors on arterial smooth muscle cells (ASMC). β₂-adrenergic receptors of ASMC mediate vasodilation through agonist mediated c-AMP production. Previous reports have described these receptors on freshly isolated blood vessels. This study demonstrates the presence of β₂-adrenergic receptors on cultured rat ASMC and that these receptors are functional. β-adrenergic receptor binding was measured using [³H]-dihydroalprenolol (DHA) binding to the membrane of cultured ASMC from normotensive Wistar-Kyoto rats. The ASMC β-adrenergic receptors have a Kd of 0.56 ± 0.16 nM and a Bmax of 57.2 ± 21.7 fmol/mg protein. Competition binding studies revealed a much greater affinity of these receptors for epinephrine than norepinephrine, indicating the preponderance of a β₂-adrenergic receptor subtype. Isoproterenol stimulation of cultured ASMC resulted in a 14 ± 7 fold increase in intracellular c-AMP content of these cells indicating these receptors are functional. β-adrenergic receptors of cultured ASMC provide an excellent system in which the association between hypertension and observed β-adrenergic receptor differences can be further explored.