Characterization of alpha- and beta-adrenergic and angiotensin receptors in cultured vascular smooth muscle cells of rat aorta.

To study the cellular mechanism of vascular responsiveness by vasoactive hormones, such as catecholamines and angiotensin (A), the vascular smooth muscle cells (VSMC) of two clonal cell lines (A7r5 and A10) from rat embryo, and of adult rat aorta were established in culture. Binding studies using 125I-labeled-hydroxyphenylethylaminoethyltetralone as an alpha-adrenergic ligand and 125I-labeled-iodocyanopindolol as a beta-adrenergic ligand, revealed that cultured VSMCs contain both alpha- and beta-adrenergic receptors; the binding was specific, rapid, reversible, and saturable. alpha-Adrenergic receptors appear to be a single class of high-affinity binding sites with an apparent dissociation constant (Kd) of approximately 2 X 10(-10) M and a maximal binding capacity (Bmax) of approximately 300,000-400,000 sites/cell, and exclusively of alpha 1-subtype that is responsible for smooth muscle contraction. On the other hand, beta-adrenergic receptors show almost comparable characteristics with the apparent Kd of approximately 0.7-1.1 X 10(-10) M and Bmax of approximately 50,000-130,000 sites/cell, and consist predominantly of beta 2-subtype that mediates smooth muscle relaxation. Furthermore, beta-adrenergic receptors are coupled to adenylate cyclase system, of which activation by beta-agonists induces intracellular cyclic AMP formation. In contrast, the binding of 125I-labeled-AII was demonstrated only in A7r5. The binding declined rapidly during incubation possibly due to faster degradation of AII by proteolytic enzyme(s). AII receptors appear to be a single class of high-affinity binding sites with the apparent Kd of approximately 0.9 X 10(-10) M and Bmax of approximately 11,000 sites/cell, of which affinity is higher than any of vascular AII receptors previously reported.(ABSTRACT TRUNCATED AT 250 WORDS)