Intracellular Pathways Involved in Upregulation of Vascular Endothelin Type B Receptors in Cerebral Arteries of the Rat

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Abstract
Background and Purpose— Previous studies have shown that contractile endothelin type B (ET B ) receptors are upregulated in cerebral arteries after experimental focal cerebral ischemia. The aim of this study was to examine the upregulation of contractile ET B receptors in cerebral arteries after organ culture and to elucidate the intracellular pathways involved. Methods— Rat middle cerebral arteries (MCAs) were incubated with or without inhibitors. The vessels were mounted in myographs, and the contractile responses to endothelin-1 (ET-1) (ET A and ET B receptor agonist) and sarafotoxin 6c (ET B receptor agonist) were measured. Levels of ET B receptor mRNA were measured with real-time polymerase chain reaction. Results— In fresh MCA, sarafotoxin 6c had no contractile effect. However, after organ culture, a strong concentration-dependent contraction was induced. ET-1 produced a strong contraction, in which the E max was unaffected by organ culture but the EC 50 was decreased with time. The sarafotoxin 6c–induced contraction after 24 hours of organ culture was attenuated by the transcriptional inhibitor actinomycin D and the translational inhibitor cycloheximide as well as the protein kinase C inhibitor Ro-31-8220. Real-time polymerase chain reaction revealed that the mRNA levels of the ET B receptor were increased after organ culture compared with fresh vessels. Actinomycin D and Ro-31-8220 diminished the enhanced mRNA levels considerably. Conclusions— The results suggest that, in fresh MCA, the ET A receptor is the most prominent subtype, while after organ culture ET B receptors also contribute to the contraction. This upregulation is due to de novo transcription of receptors. Protein kinase C is involved in the upregulation as Ro-31-8220 attenuates the contraction and the mRNA increase.