Modes of determining beta-adrenoceptor number in human mononuclear leucocytes.
Inhibition of total 125I-ICYP binding to intact human mononuclear leucocytes at 32 degrees by propranolol and (+/-) CGP-12177 was biphasic. The high affinity component of 125I-ICYP binding, representing approximately 30% of total, was stereospecific, while the low affinity binding site was inhibited without stereospecificity. (-) Isoproterenol inhibited the high affinity component of 125I-ICYP binding only, with low affinity. By performing binding studies in intact cells at 4 degrees or in broken cell preparations at 37 degrees, the fraction of total 125I-ICYP binding representing specific binding was increased, and agonist affinity was high. Inhibition of 3H-CGP-12177 binding to intact cells at 32 degrees demonstrated a high fraction of specific binding and high agonist affinity. Computer-assisted analysis of total radioligand binding determined over a broad concentration range revealed two populations of saturable 125I-ICYP binding sites in intact cells as well as in broken cell preparations, while 3H-CGP-12177 binding demonstrated only one saturable binding site. The number of high affinity 125I-ICYP binding sites was comparable to the number of saturable 3H-CGP-12177 binding sites. Receptor numbers determined by analysis of total radioligand binding were comparable to receptor numbers determined by subtraction of non-specific binding, determined in the presence of a high concentration of competing ligand. Analysis of total radioligand binding was found to be a better procedure because it eliminates the use of an arbitrary concentration of unlabelled ligand and improves the accuracy of the assay.
D000293:Adolescent; D000319:Adrenergic beta-Antagonists; D000328:Adult; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D020120:Iodocyanopindolol; D008297:Male; D008875:Middle Aged; D009504:Neutrophils / Q000032:analysis*; D010869:Pindolol / Q000031:analogs & derivatives; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta / Q000032:analysis*; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D013696:Temperature
D000319:Adrenergic beta-Antagonists; D007457:Iodine Radioisotopes; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; D020120:Iodocyanopindolol; D010869:Pindolol; C033394:CGP 12177