Reduced Mechanical Stretch Induces Enhanced Endothelin B Receptor-Mediated Contractility via Activation of Focal Adhesion Kinase and Extracellular Regulated Kinase 1/2 in Cerebral Arteries from Rat.

Cerebral ischaemia results in enhanced endothelin B ( ET_B) receptor-mediated contraction and receptor protein expression in the affected cerebrovascular smooth muscle cells ( SMC). Organ culture of cerebral arteries is a method to induce similar alterations in ET_B receptor expression. We suggest that rapid and sustained reduction in wall tension/stretch is a possible trigger mechanism for this vascular remodelling. Isolated rat middle cerebral artery ( MCA) segments were incubated in a wire myograph with or without mechanical stretch, prior to assessment of their contractile response to the selective ET_B receptor agonist sarafotoxin 6c. The involvement of extracellular regulated kinase ( ERK) 1/2 and focal adhesion kinase ( FAK) was studied by their specific inhibitors U0126 and PF-228, respectively. Compared with their stretched counterparts, unstretched MCA segments showed a significantly increased ET_B receptor-mediated contractile response after 12 hr of incubation, which was attenuated by either U0126 or PF-228. The functionally increased ET_B-mediated contractility could be attributed to two different mechanisms: (i) a difference in ET_B receptor localization from primarily endothelial expression to SMC expression and (ii) an increased calcium sensitivity of the SMCs due to an increased expression of the calcium channel transient receptor potential canonical 1. Collectively, our results present a possible mechanism linking lack of vessel wall stretch/tension to changes in ET_B receptor-mediated contractility via triggering of an early mechanosensitive signalling pathway involving ERK1/2 and FAK signalling. A mechanism likely to be an initiating factor for the increased ET_B receptor-mediated contractility found after cerebral ischaemia. [ABSTRACT FROM AUTHOR]