Regulation of alpha(2)-adrenoceptors in human vascular smooth muscle cells

• Published in: American journal of physiology. Heart and circulatory physiology 2004-01, Vol.286 (1), p.H59-H67
• Main Authors: Chotani, Maqsood A, Mitra, Srabani, Su, Baogen Y, Flavahan, Sheila, Eid, Ali H, Clark, K Reed, Montague, Christine R, Paris, Herve, Handy, Diane E, Flavahan, Nicholas A
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Arterioles - cytology; Arterioles - metabolism; Blood Physiological Phenomena; Female; Humans; Male; Middle Aged; Mitogen-Activated Protein Kinases - physiology; Muscle, Smooth, Vascular - cytology; Muscle, Smooth, Vascular - metabolism; Myocytes, Smooth Muscle - metabolism; p38 Mitogen-Activated Protein Kinases; Promoter Regions, Genetic - physiology; Protein Isoforms - metabolism; Receptors, Adrenergic, alpha-2 - genetics; Receptors, Adrenergic, alpha-2 - metabolism
• ISSN: 0363-6135
• DOI: 10.1152/ajpheart.00268.2003

This study analyzed the regulation of alpha2-adrenoceptors (alpha2-ARs) in human vascular smooth muscle cells (VSMs). Saphenous veins and dermal arterioles or VSMs cultured from them expressed high levels of alpha2-ARs (alpha2C > alpha2A, via RNase protection assay) and responded to alpha2-AR stimulation [5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (UK-14,304, 1 microM)] with constriction or calcium mobilization. In contrast, VSMs cultured from aorta did not express alpha2-ARs and neither cultured cells nor intact aorta responded to UK-14,304. Although alpha2-ARs (alpha2C >> alpha2A) were detected in aortas, alpha2C-ARs were localized by immunohistochemistry to VSMs of adventitial arterioles and not aortic media. In contrast with aortas, aortic arterioles constricted in response to alpha2-AR stimulation. Reporter constructs demonstrated higher activities for alpha2A- and alpha2C-AR gene promoters in arteriolar compared with aortic VSMs. In arteriolar VSMs, serum increased expression of alpha2C-AR mRNA and protein but decreased expression of alpha2A-ARs. Serum induction of alpha2C-ARs was reduced by inhibition of p38 mitogen-activated protein kinase (MAPK) with 2 microM SB-202190 or dominant-negative p38 MAPK. UK-14,304 (1 microM) caused calcium mobilization in control and serum-stimulated cells: in control VSMs, the response was inhibited by the alpha2A-AR antagonist BRL-44408 (100 nM) but not by the alpha2C-AR antagonist MK-912 (1 nM), whereas after serum stimulation, MK-912 (1 nM) but not BRL-44408 (100 nM) inhibited the response. These results demonstrate site-specific expression of alpha2-ARs in human VSMs that reflects differential activity of alpha2-AR gene promoters; namely, high expression and function in venous and arteriolar VSMs but no detectable expression or function in aortic VSMs. We found that alpha2C-ARs can be dramatically and selectively induced via a p38 MAPK-dependent pathway. Therefore, altered expression of alpha2C-ARs may contribute to pathological changes in vascular function.