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

Kinin B-1 receptors on rabbit aorta smooth muscle cells in culture wer e investigated. [H-3]Des-Arg(10)-kallidin labeled a single site in cel ls at early passage with an equilibrium dissociation constant of 258 p M and a maximal binding density of approximately 680 sites/cell. Treat ment of the same cells for 18 h with epidermal growth factor increased the binding density over 6-fold without affecting the ligand's affini ty. At latter passages, the density of binding sites was found to incr ease and the growth factor had a much less pronounced effect. The rank order of potencies for agonist inhibition of binding (des-Arg(10)-kal lidin > 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. T he agonists were found to stimulate phosphoinositide hydrolysis in the smooth muscle cells with an order of potencies that reflected their b inding assay activities. Des-Arg(9)[Leu(8)] BK blocked the des-Arg(10) -kallidin response with a potency consistent with its known B-1 recept or activity while Hoe 140 was inactive. These results demonstrate the presence of inducible B-1 receptors on rabbit aorta smooth muscle cell s in culture that couple to phospholipase C activation. These cells sh ould be useful in future studies of the mechanisms and factors involve d in the regulation of expression of the B-1 receptor.