No abstract

1 This study examines the importance of mitogen-activated protein kinases (MAPKs) in upregulation of endothelin type B (ET B ) receptors. 2 Rat middle cerebral arteries (MCAs) were incubated for 24 h with or without kinase inhibitors. Vessel segments were mounted in myographs and the contractile responses to endothelin-1 (ET-1; ET A and ET B receptor agonist) and sarafotoxin 6c (S6c; ET B receptor agonist) were studied. We used realtime PCR to measure the receptor mRNA levels. An ELISA assay showed the activation of ERK1/2 kinases after 3 h. Immunohistochemistry revealed the presence of ET B receptors on the vessels. 3 After organ culture, S6c induced vasoconstriction. Incubation with the MEK/ERK inhibitors U0126 and SB386023 diminished the contractile response to S6c. The p38 MAPK inhibitor SB239063 did not affect the S6c-induced contraction. 4 The ET-1-induced vasoconstriction was increased after incubation with SB386023 or SB239063, while unaffected by U0126. 5 The ET B receptor mRNA levels were diminished by SB386023 and U0126. The ET A receptor mRNA levels were unaffected. 6 The levels of activated ERK1/2 kinases were significantly higher after 3 h of organ culture as compared to fresh vessels. 7 The level of ET B receptor protein on the smooth muscle cells of the MCA, visualised by immunohistochemistry, was somewhat diminished by SB386023. 8 Our results show that the ERK1/2 MAPK is important in the upregulation of contractile ET B receptors in MCA after organ culture. Since there is a similar upregulation in models of focal ischaemia and subarachnoid haemorrhage, this may be an important pathophysiological event.

Cigarette smoke is a strong risk factor for cardiovascular disease. However, the underlying molecular mechanisms that lead to cigarette smoke-associated cardiovascular disease remain elusive. With functional and molecular methods, we demonstrate for the first time that lipid-soluble cigarette smoke particles (dimethylsulfoxide-soluble cigarette smoke particles; DSP) increased the expression of endothelin type B (ET(B)) receptors in arterial smooth muscle cells. The increased ET(B) receptors in arterial smooth muscle cells was documented as enhanced contractility (sensitive myograph technique), elevated levels of ET(B) receptor mRNA (quantitative real-time PCR), and protein expressions (immunohistochemistry and Western blotting). Intracellular signaling was studied with Western blotting and phosphoELISA; this revealed that DSP induced extracellular-regulated protein kinases 1 and 2 (ERK1/2), p38, and nuclear factor-kappaB (NF-kappaB) phosphorylation within 3 h. Blocking ERK1/2, p38, or NF-kappaB activation by their specific inhibitors significantly attenuated the DSP-induced upregulation of ET(B) receptor-mediated contraction and both ET(B) receptor mRNA and protein expression. In addition, dexamethasone abolished the DSP-induced upregulation of ET(B) receptor-mediated contraction. In conclusion, upregulation of ET(B) receptors by DSP in arterial smooth muscle cells involves activation of mitogen-activating protein kinases (ERK1/2 and p38) and the downstream transcriptional factor NF-kappaB pathways.

The altered receptor profile observed may represent the final stage in the series of events leading from SAH to actual spasm of the artery. The pharmacological data for the ET(B) receptor suggest complex interactions between normally present ET(A) receptors and up-regulated ET(B) receptors.