| Abstract: | Beta adrenergic receptors have been previously characterized in human neutrophil sonicates. In the present study the intact neutrophil has been assessed for the number and affinity of beta adrenergic binding sites by using the antagonist DNA. Agonist and antagonist potencies, characterized by their effect on DHA binding and cyclic AMP accumulation, are compared with agonist inhibition of lysosomal enzyme (beta glucuronidase) release. Criteria for beta adrenergic receptor identification were successfully demonstrated. At 30 degrees C, beta adrenergic binding was rapid (t 1/2 2 min) and reversible (t 1/2 9 min). Receptor binding was saturable, revealing approximately 900 high-affinity receptors per neutrophil with DHA concentrations of 0.1 to 10 nM. By utilizing both equilibrium and kinetic techniques, the KD was determined to be approximately 0.6 nM. Agonists and antagonists competed for DHA binding in a manner consistent with their effect on cyclic AMP generation. Rank order potency was suggestive of a beta-2 receptor: isoproterenol greater than epinephrine greater than norepinephrine. Stereoselectivity was shown by the greater potency of L-propranolol compared to the D isomer. A high degree of receptor-adenylate cyclase coupling efficiency was suggested by the observation that with only 1% receptor occupancy isoproterenol stimulated 50% maximal cyclic AMP generation. Finally, there was an excellent correlation between the isoproterenol concentration which resulted in 50% of maximal inhibition of beta glucuronidase release (Ki) and that causing 50% maximal cyclic AMP stimulation (Kact), suggestive of a close relationship between beta adrenergic-induced adenylate cyclase activation and beta adrenergic regulation of neutrophil lysosomal enzyme release. The data presented suggest that the use of the intact neutrophil for study of the beta adrenergic receptor is feasible and may provide information which is considerably more closely related to modulation of physiological function by neurohormones than is possible with disrupted cell preparations. |
