Steroid sensitivity of norepinephrine uptake by human bronchial arterial and rabbit aortic smooth muscle cells

We have shown that an inhaled glucocorticosteroid (GS) causes alpha(1)-adrenergic antagonist-blockable, rapid, and transient bronchial vasoconstriction in healthy and asthmatic subjects. Steroids inhibit norepinephrine (NE) uptake by non-neuronal cells, thereby increasing NE concentration at alpha-adrenergic receptor sites. This could explain the GS-induced bronchial vasoconstriction. We therefore studied expression of the steroid-sensitive extraneuronal monoamine transporter (EMT) and steroid sensitivity of NE uptake in human bronchial artery and rabbit aorta (as a substitute for the limited supply of human bronchial artery). NE uptake was measured using a semiquantitative, sucrose-potassium phosphate-glyoxylic acid fluorescence method that we newly adapted for use in single cells. Both human bronchial arteries and rabbit aorta expressed messenger RNA for EMT, and steroids blocked NE uptake into freshly dissociated human bronchial arterial and rabbit aortic smooth-muscle cells (SMCs). In the latter, inhibition of NE uptake by steroids was not altered, either by a protein synthesis inhibitor (cycloheximide) or by a transcription inhibitor (actinomycin D), and corticosterone made membrane-impermeant by conjugation to bovine serum albumin inhibited NE uptake equipotently. These data show that NE uptake into bronchial arterial and rabbit aortic SMCs is sensitive to steroids, possibly mediated by EMT, and suggest a mechanism for GS-induced bronchial vasoconstriction.