| Abstract: | Human PMNs have well-described responses to beta-adrenergic catecholamines; these include elevation of cellular levels of cyclic AMP and inhibition of the release of lysosomal contents. Using the radioactive beta-adrenergic antagonist (-)-3H]DHA in direct ligand-binding studies, we have identified and characterized beta-adrenergic receptors on particulate preparations of PMNs. These particulates bind DHA rapidly (t1/2 less than 1 min) and reversibly (t1/2 = 8 to 9 min). DHA binding is saturable and of high affinity (dissociation constant = 1 to 5 nM) and low capacity (870 +/- 128 receptors/cell, mean +/- S.D.) to a single class of binding sites. Competition for DHA binding sites by both beta-adrenergic agonists and antagonists is stereoselective (-)-isomers more potent that (+)-isomers]. The rank order of potency of adrenergic agents in such competition studies indicates that these receptors are of the beta2 type. Since PMNs can be obtained in high purity with relative ease, the combined use of pharmacologic and ligand-binding studies in PMNs provide a useful system for studying beta-adrenergic receptors and their function in human subjects. |
