CHARACTERIZATION OF ALPHA-ADRENOCEPTOR GENE-EXPRESSION IN ARTERIAL AND VENOUS SMOOTH-MUSCLE

Six genes coding for three unique alpha1- (1A, 1B, 1C) and three unique alpha2- (2A, 2B, 2C) adrenergic receptor (AR) subtypes have been cloned. Ligand binding and contractile studies have demonstrated that both alpha1- and alpha2-ARs can exist on vascular smooth muscle (VSM) cells, although less is known about the relative distribution and specific subtypes in different vascular segments. In the present study polymerase chain reaction (PCR) analysis was used to characterize the species of alpha-AR messenger RNA (mRNA) present in freshly isolated rat thoracic aortic media and vena cava and in cultured VSM cells (passage 2) derived from both sources. To prevent possible contamination of VSM mRNA, aortic media was separated from adventitia, and vessels were denuded of endothelial cells. Oligonucleotide primers specific for each of the six adrenergic genes were synthesized and used to probe for the presence of alpha-AR mRNA species after reverse transcription of total cellular RNA to cDNA. PCR-amplified AR transcripts were distinguished by the size of amplified DNA fragments and unique restriction endonuclease cleavage. Expression of alpha1C- or alpha2C-mRNA was not detected in vascular tissues or cultured VSM cells, although the alpha2C-primers detected the expected alpha2C expression in cerebral cortex. Only alpha1A-mRNA was detected in aortic adventitia. VSM from aorta expressed alpha1A-, alpha1B-, and alpha2A-MRNA, and this pattern was preserved in cultured aortic VSM. Vena cava also expressed both alpha1A and alpha1B; however only alpha2B-MRNA was detected. In cultured vena cava VSM this pattern was preserved, but in addition, alpha2A expression was induced. These results suggest that arterial and venous smooth muscle may express similar alpha1- but different alpha2-adrenoceptors. Moreover, culture conditions may alter alpha-adrenergic gene expression.