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

Abstract

Hypoxia inhibits beta(2)-adrenergic receptor (beta(2)-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 beta(2)-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% O(2)) 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 beta(2)-AR assessed by (-)-[(125)I]iodocyanopindolol binding was decreased in hypoxia (-22%). Hypoxia did not affect terbutaline binding affinity to beta(2)-AR. Hypoxia decreased G(s) protein levels by 27%, whereas no change was observed in G(i1/2), G(i3), and Gbeta subunits. Forskolin-stimulated cAMP production was not inhibited by hypoxia. Pertussis toxin (PTX; 0.5 microg/ml, 2 h), an inhibitor of G(i/o) proteins, restored terbutaline-stimulated cAMP production of hypoxic ATII cells to normoxic control values. Cholera toxin (CTX)-stimulated G(s) protein activity did not change in hypoxia. Hypoxia increased the sensitivity of beta(2)-AR to desensitization. These results indicate that despite the decrease in G(s) protein level G(s) protein was still functional and that hypoxia impairs beta(2)-AR signaling due to an increased activity of G(i/o) proteins.