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)-adr energic antagonist-blockable, rapid, and transient bronchial vasoconstricti on in healthy and asthmatic subjects. Steroids inhibit norepinephrine (NE) uptake by non-neuronal cells, thereby increasing NE concentration at a-adre nergic receptor sites. This could explain the GS-induced bronchial vasocons triction. We therefore studied expression of the steroid-sensitive extraneu ronal monoamine transporter (EMT) and steroid sensitivity of NE uptake in h uman bronchial artery and rabbit aorta (as a substitute for the limited sup ply of human bronchial artery). NE uptake was measured using a semiquantita tive, sucrose-potassium phosphate-glyoxylic acid fluorescence method that w e newly adapted for use in single cells. Both human bronchial arteries and rabbit aorta expressed messenger RNA for EMT, and steroids blocked NE uptak e into freshly dissociated human bronchial arterial and rabbit aortic smoot h-muscle cells (SMCs). In the latter, inhibition of NE uptake by steroids w as not altered, either by a protein synthesis inhibitor (cycloheximide) or by a transcription inhibitor (actinomycin D), and corticosterone made membr ane-impermeant by conjugation to bovine serum albumin inhibited NE uptake e quipotently. These data show that NE uptake into bronchial arterial and rab bit aortic SMCs is sensitive to steroids, possibly mediated by EMT, and sug gest a mechanism for GS-incluced bronchial vasoconstriction.