In vitro hypoxia impairs β2-adrenergic receptor signaling in primary rat alveolar epithelial cells

Abstract

Hypoxia inhibits β2-adrenergic receptor (β2-AR) signaling in a variety of tissues, but effects in alveolar epithelium are unclear. We therefore examined the effect of 24 h of hypoxia on β2-AR function in primary rat alveolar epithelial [alveolar type II (ATII)] cells. ATII cells were isolated, cultured to confluence, and incubated in normoxia or hypoxia (3% O2) for 24 h. Hypoxia decreased maximal terbutaline-stimulated cAMP production by 37%; potency of terbutaline was not affected. Reoxygenation (3 h) reversed this effect. Density of β2-AR assessed by (−)-[125I]iodocyanopindolol binding was decreased in hypoxia (−22%). Hypoxia did not affect terbutaline binding affinity to β2-AR. Hypoxia decreased Gsprotein levels by 27%, whereas no change was observed in Gi1/2, Gi3, and Gβ subunits. Forskolin-stimulated cAMP production was not inhibited by hypoxia. Pertussis toxin (PTX; 0.5 μg/ml, 2 h), an inhibitor of Gi/oproteins, restored terbutaline-stimulated cAMP production of hypoxic ATII cells to normoxic control values. Cholera toxin (CTX)-stimulated Gsprotein activity did not change in hypoxia. Hypoxia increased the sensitivity of β2-AR to desensitization. These results indicate that despite the decrease in Gsprotein level Gsprotein was still functional and that hypoxia impairs β2-AR signaling due to an increased activity of Gi/oproteins.