Presence and function of ß-adrenergic receptors in primary equine bronchial epithelia cells.

The ß-adrenergic receptor (ß-AR) plays an important role in regulating a variety of cell and organ functions in different animal species and is an important target in asthma pathogenesis and therapy. The ß-AR expression and function in equine bronchial epithelial cells (EBEC) were not known but innervation and significant decrease in receptor level were reported in the equine bronchial tissues from asthmatic horses. 125I-iodocyanopindolol (ICYP) binding studies were undertaken in primary freshly isolated and cultured EBEC to identify the presence of the ß-ARs. The receptor distribution was assessed using subtype-selective ß-AR antagonists (ICI 118 551 (ß2) and CGP 20712A (ß1). The ß-AR function was confirmed by measuring the agonist-induced intracellular cAMP accumulation in freshly isolated and cultured EBEC. In both freshly isolated and cultured EBEC, the specific ICYP binding was saturable and of high affinity. The maximal receptor density (Bmax) was 9763 ± 140 binding sites/cell (mean ± SEM, n = 7) and 10575 ± 194 binding sites/cell (mean ± SEM, n = 5) in freshly isolated and cultured EBEC, respectively. The receptor affinity to the ligand (KD) was also not different between the two cell conditions. ICI 118.551 displaced ICYP with 25 000-fold higher affinity than CGP 20712A. Moreover, in both fresh isolated and cultured EBEC, cAMP-accumulation was stimulated with a rank-order of potency of isoproterenol > adrenaline > noradrenaline. These results highlight the ß2-AR to be a key subtype in both freshly isolated and cultured primary EBEC.

Distribution and properties of cardiac and pulmonary ß-adrenergic receptors in corn snakes (Pantherophis guttatus) and Boa constrictor (Boa constrictor).

The aim of the present study was to characterize ß-adrenergic receptors in the snake heart and lung of corn and Boa constrictor snakes. The ß-adrenergic receptor binding sites were studied in purified heart and lung membranes using the specific ß-adrenergic receptor antagonist [125J]-iodocyanopindolol (ICYP) and subtypes using selective ß1-adrenergic receptor antagonist CGP-20712A and selective ß2-adrenergic receptor antagonist ICI-118.551. A saturable and specific ß-adrenergic receptor binding site was detected in cardiac membranes with maximal receptor density (Bmax) of 43.99 ±â€¯3.86 fmol/mg protein (corn snake) and 58.07 ±â€¯2.88 fmol/mg protein (Boa constrictor) as well as KD of 24.21 ±â€¯7.38 pM (corn snake) and 21.48 ±â€¯3.85 pM (Boa constrictor) and in lung membranes (Bmax fmol/mg protein: 55.95 ±â€¯16.28 (corn snake) and 107.00 ±â€¯14.21 (Boa constrictor); KD pM: 71.25 ±â€¯21.92 (corn snake) and 55.04 ±â€¯18.68 (Boa constrictor)). Competition-binding studies showed ß-adrenergic receptors with low affinities to the ß2-selective adrenergic receptor antagonist and high affinity binding to ß1-selective adrenergic receptor antagonist in both heart and lung tissues of both snake species, suggesting the presence of high population of the post-synaptic ß1-adrenergic receptor subtype. It seems that the presence of the predominant ß1-subtype also in lung tissues may indicate the importance of the vascular system in the snake lung.