title: Functional angiotensin II receptors in cultured vascular smooth muscle cells.
abstract: To study cellular mechanisms influencing vascular reactivity, vascular smooth muscle cells (VSMC) were obtained by enzymatic dissociation of the rat mesenteric artery, a highly reactive, resistance-type blood vessel, and established in primary culture. Cellular binding sites for the vasoconstrictor hormone angiotensin II (AII) were identified and characterized using the radioligand 125I-angiotensin II. Freshly isolated VSMC, and VSMC maintained in primary culture for up to 3 wk, exhibited rapid, saturable, and specific 125I-AII binding similar to that seen with homogenates of the intact rat mesenteric artery. In 7-d primary cultures, Scatchard analysis indicated a single class of high-affinity binding sites with an equilibrium dissociation constant (Kd) of 2.8 +/- 0.2 nM and a total binding capacity of 81.5 +/- 5.0 fmol/mg protein (equivalent to 4.5 x 10(4) sites per cell). Angiotensin analogues and antagonists inhibited 125I-AII binding to cultured VSMC in a potency series similar to that observed for the vascular AII receptor in vivo. Nanomolar concentrations of native AII elicited a rapid, reversible, contractile response, in a variable proportion of cells, that was inhibited by pretreatment with the competitive antagonist Sar1,Ile8-AII. Transmission electron microscopy showed an apparent loss of thick (12-18 nm Diam) myofilaments and increased synthetic activity, but these manifestations of phenotypic modulation were not correlated with loss of 125I-AII binding sites or hormonal responsiveness. Primary cultures of enzymatically dissociated rat mesenteric artery VSMC thus may provide a useful in vitro system to study cellular mechanisms involved in receptor activation-response coupling, receptor regulation, and the maintenance of differentiation in vascular smooth muscle.
mesh_terms: D000804:Angiotensin II / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D008638:Mesenteric Arteries; D008854:Microscopy, Electron; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D011945:Receptors, Angiotensin / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*
chemical_list: D011945:Receptors, Angiotensin; D011956:Receptors, Cell Surface; D000804:Angiotensin II