Human neutrophils and HL-60 cells do not possess α 2-adrenoceptors

Abstract

Human neutrophils have been reported to possess both α 2- and β 2-adrenoceptors. While activation of β 2-adrenoceptors is known to inhibit N formyl- L-methionyl- L-leucyl- L-phenylalanine (fMLP)-induced Superoxide anion (O − 2) production, the functional role of α 2-adrenoceptors is not known. We studied the effects of a range of structurally unrelated α 2-adrenoceptor agonists on fMLP-induced O − 2 production and UTP-induced increases in cytosolic free calcium concentration ([Ca 2+] i) in human neutrophils. No effect of α 2-adrenoceptor agonists was seen on either fMLP-induced O − 2 production or UTP-induced increases in [Ca 2+] i. α 2-Adrenoceptor agonists by themselves had no effect on either O − 2 production or [Ca 2+] i. We then studied a model for neutrophils, differentiated HL-60 cells and human erythroleukaemia (HEL) cells, a cell line known to possess α 2-adrenoceptors. While the α 2-adrenoceptor agonists 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK 14304) and 5-allyl-2-amino-5,6,7,8-tetrahydro-4 H-thiazolo-[4,5- d]azepin-dihydrochloride increased the [Ca 2+] i in HEL cells, they had no effect by themselves on either [Ca 2+] i or UTP-induced increases in [Ca 2+] i in differentiated HL-60 cells. Activation of high-affinity GTPase by UK 14304 was seen in membranes from HEL cells but not in membranes from differentiated HL-60 cells. Similarly, a selective α 2-adrenoceptor antagonist, [ 3H]2-(2-methoxy-l, 4-benzodioxan-2yl)-2 imidazoline, bound specifically and saturably to membranes from HEL cells, but not to membranes from HL-60 promyelocytes or differentiated HL-60 cells. Taken together, these data suggest that neither HL-60 promyelocytes nor differentiated HL-60 cells possess α 2-adrenoceptors, and that the lack of functional responses to α 2-adrenoceptor agonists in human neutrophils is due to the absence of α 2-adrenoceptors.