Transcriptional up-regulation in expression of 5-hydroxytryptamine2A and transcriptional down-regulation of angiotensin II type 1 receptors during organ culture of rat mesenteric artery

The purpose of this study was to investigate in rat mesenteric artery if there is up-regulation of 5-hydroxytryptamine (5-HT) receptors and angiotensin II receptors and the potential role of protein kinase C activation in the smooth muscle cells during organ culture. Angiotensin II, 5-HT and potassium induced contraction of ring segments without endothelium, monitored by a sensitive in vitro pharmacology method. After the culture of the arterial ring segments for 24 hr, the concentration-contraction curves induced by 5-HT slightly shifted towards to the left with pEC(50) from 6.64 +/- 0.11 to 6.84 +/- 0.11 and a significant increase in E-max from 147 +/- 11% to 246 +/- 15% (P<0.05), compared with that obtained in fresh segments. In contrast, the angiotensin 11 concentration-contraction curve only showed a significant decrease in E-max from 99 +/- 10% to 37 +/- 8%. Specific antagonists for the 5-HT type 2A receptors (5-HT2A) and angiotensin II type 1 receptors (AT(1)) demonstrated that the contractions occurred via 5-HT2A and AT(1) receptors, respectively. Real-time PCR revealed that the 5-HT2A receptor mRNA was up-regulated in parallel with the contractile response while there was a downregulation of AT(1) receptor mRNA. Transcriptional inhibitor actinomycin D and specific protein kinase C inhibitor Ro31-8220 demonstrated that it was a transcriptional mechanism with involvement of protein kinase C that regulated the enhanced expression of 5-HT2A receptors in the mesenteric artery