Regulation of alpha(2)-adrenoceptors in human vascular smooth muscle cells.
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.
Chotani
Maqsood A
MA
Davis Heart and Lung Research Institute, Ohio State University, Columbus, OH 43210, USA. chotani-1@medctr.osu.edu
Mitra
Srabani
S
Su
Baogen Y
BY
Flavahan
Sheila
S
Eid
Ali H
AH
Clark
K Reed
KR
Montague
Christine R
CR
Paris
Herve
H
Handy
Diane E
DE
Flavahan
Nicholas A
NA
D000293:Adolescent; D000328:Adult; D001160:Arterioles / Q000166:cytology / Q000378:metabolism; D001790:Blood Physiological Phenomena; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000502:physiology; D020033:Protein Isoforms / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000235:genetics / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases
D020033:Protein Isoforms; D018341:Receptors, Adrenergic, alpha-2; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases