Importance of ERK1/2 in upregulation of endothelin type B receptors in cerebral arteries

1 This study examines the importance of mitogen-activated protein kinases (MAPKs) in upregulation of endothelin type B (ETB) 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; ETA and ETB receptor agonist) and sarafotoxin 6c (S6c; ETB receptor agonist) were studied. We used real-time 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 ETB 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 ETB receptor mRNA levels were diminished by SB386023 and U0126. The ETA 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 ETB 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 ETB 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.