1 The long-acting b 2 -adrenoceptor agonist formoterol (10 À10 -10 À6 M) inhibited the IgE-dependent release of histamine from human lung mast cells in a concentration-dependent manner. Formoterol was more potent and a full agonist relative to the nonselective b-adrenoceptor agonist isoprenaline. By contrast, the long-acting b 2 -adrenoceptor agonist salmeterol (10 À10 -10 À6 M) was about two-thirds less efficacious than either formoterol or isoprenaline as an inhibitor of histamine release. 2 Isoprenaline, formoterol and salmeterol (all at 10 À5 M) increased total cell cAMP levels in mast cells over basal by 361790 (Po0.05), 321789 (Po0.05) and 64724% (P40.05), respectively. 3 Long-term (24 h) incubation of mast cells with formoterol (10 À6 M) or salmeterol (10 À6 M) essentially abolished the subsequent ability of isoprenaline to inhibit histamine release. Both formoterol and salmeterol were more effective at inducing the functional desensitisation than isoprenaline (10 À6 M) or the short-acting b 2 -adrenoceptor agonist salbutamol (10 À6 M). 4 The desensitisation induced by long-term treatments with salmeterol and formoterol was specific for b 2 -adrenoceptor-mediated inhibition of histamine release as the inhibitory effects of alternative cAMP-elevating compounds, prostaglandin E 2 , a receptor-mediated activator of adenylate cyclase, and forskolin, a direct activator of adenylate cyclase, were unaffected by desensitising treatments. 5 Radioligand binding studies were performed to determine b 2 -adrenoceptor density in cell membranes after pretreatment (24 h) of cells with agonists. Isoprenaline, formoterol and salmeterol (all at 10 À6 M) reduced b 2 -adrenoceptor density by 1375 (P40.05), 49713 (Po0.05) and 35717% (P40.05), respectively. 6 These data indicate that long-term exposure of mast cells to both salmeterol and formoterol can cause substantial levels of desensitisation to b 2 -adrenoceptor-mediated responses in mast cells.

These studies indicate that although syk may play an important role in mediating degranulation, the relative level of syk expression does not govern human lung mast cell releasability. Identification of the mechanisms that govern IgE-dependent activation of human lung mast cells is likely to be of wider clinical significance, given the central role that mast cells play in the development of allergic asthma.

Background: The aim of the present study was to establish whether polymorphisms, especially those within the promoter region, of the β 2 -adrenoceptor gene (ADRB2) influence β 2 -adrenoceptor expression in human lung. Methods:The density of β-adrenoceptors in human lung tissue (n=88) was determined by saturation binding using the radioligand, iodinated cyanopindolol. Discrimination of β 1 -and β 2 -adrenoceptors was determined using the highly selective β 1 -adrenoceptor antagonist, CGP20712A. Genotype was determined at 5 positions of ADRB2 previously reported as polymorphic. Potential influences of single nucleotide polymorphisms (SNPs) within the promoter region (-367, -47) and coding block (46, 79, 491) of ADRB2 on β 2 -adrenoceptor expression were investigated. Results:The density of β 2 -adrenoceptors was variable among the 88 lung preparations studied ranging from 17 to 177 fmol/mg protein (mean±S.E.M., 72±4 fmol/mg protein).There was no influence of genotype on β 2 -adrenoceptor expression for any of the polymorphisms studied except at position 491. The polymorphism at position 491C>T, leading to a change from thr to ile at amino acid 164, is uncommon. Preparations genotyped as heterozygous (126±15 fmol/mg protein; n=5) expressed significantly (P = 0.0005) higher levels of β 2 -adrenoceptor than those that were homozygous (69±4 fmol/mg protein; n=83). M A N U S C R I P T A C C E P T E D ARTICLE IN PRESS