BRADYKININ B-1 RECEPTORS IN RABBIT AORTA SMOOTH-MUSCLE CELLS IN CULTURE

Kinin B-1 receptors on rabbit aorta smooth muscle cells in culture were investigated. [H-3]Des-Arg(10)-kallidin labeled a single site in cells at early passage with an equilibrium dissociation constant of 258 pM and a maximal binding density of approximately 680 sites/cell. Treatment of the same cells for 18 h with epidermal growth factor increased the binding density over 6-fold without affecting the ligand's affinity. At latter passages, the density of binding sites was found to increase and the growth factor had a much less pronounced effect. The rank order of potencies for agonist inhibition of binding (des-Arg(10)-kallidin > des-Arg(9)-BK = kallidin > bradykinin) was consistent with the specific labeling of a B-1 receptor. Also, [H-3]des-Arg(10)-kallidin binding was potently inhibited by the B-1 receptor antagonist des-Arg(9)[Leu(8)]bradykinin but not by the B-2 receptor antagonist Hoe 140. The agonists were found to stimulate phosphoinositide hydrolysis in the smooth muscle cells with an order of potencies that reflected their binding assay activities. Des-Arg(9)[Leu(8)] BK blocked the des-Arg(10)-kallidin response with a potency consistent with its known B-1 receptor activity while Hoe 140 was inactive. These results demonstrate the presence of inducible B-1 receptors on rabbit aorta smooth muscle cells in culture that couple to phospholipase C activation. These cells should be useful in future studies of the mechanisms and factors involved in the regulation of expression of the B-1 receptor.