Determination of beta adrenoceptor density on rabbit mononuclear leukocytes

The purpose of the present study was to devise a technique for the isolation of a relatively homogeneous mononuclear leukocyte (MNL) preparation from rabbit whole blood and determine the density and affinity of beta-adrenoceptors on MNL. A modified method based upon that by Böyum was developed to maximize isolation of MNL from red blood cells (RBC), granulocytes, and platelets. The method involved an initial centrifugation to remove platelets and two centrifugations with a Ficoll solution to eliminate RBC and granulocytes. beta-Adrenoceptor density as determined with [125I]cyanopindolol and MNL membrane or whole cell preparations ranged between 317 and 360 sites per cell. Affinity for the binding sites was dependent upon whether membrane or whole cell preparations were studied, being 56.3 +/- 9.9 and 11.4 +/- 1.4 pM, respectively. Binding sites were found to be saturable and noncooperative. In addition, the binding sites demonstrated selectivity and stereospecificity for beta-adrenoceptor ligands. It is concluded that the modified method of harvesting MNL from rabbit whole blood provides a relatively homogeneous cell suspension that can be used to study the beta-adrenoceptor system.