Editorial

Aim: Wall stress‐independent signalling pathways were studied for endothelin‐1 (ET‐1)‐induced c‐fos expression in rat intact mesenteric small arteries. Methods: Arteries were kept unmounted in Krebs buffer, equilibrated for 1 h and stimulated with vasoactive substances for 15–60 min. The c‐fos mRNA expression was determined by real‐time polymerase chain reaction. Results: Stimulation with fetal bovine serum (FBS), phorbol 12‐myristate 13‐acetate (PMA) and ET‐1 caused about a doubling of c‐fos mRNA. The ET‐1‐induced c‐fos expression was steady (15–60 min) and was inhibited by the inhibitor of the ET_A receptor, BQ‐123. Platelet‐derived growth factor‐B, angiotensin II and U46619 did not cause increased c‐fos mRNA levels. The broad specificity inhibitor staurosporine inhibited the response to ET‐1, but inhibitors of Rho‐A kinase and phosphatidylinositol 3‐kinase had no effect. However, inhibitors to tyrosine kinases, the MAP kinases [extracellular signal‐regulated kinase 1/2 (ERK1/2), c‐Jun amino‐terminal kinase, p38], and to conventional protein kinase C showed no inhibition. Consistent with these findings, ET‐1 did not cause activation of ERK1/2, a finding also seen in vessels held under pressure. In contrast, ET‐1‐induced c‐fos expression was inhibited by the calcium chelator BAPTA, suggesting a role for intracellular calcium. This possibility was supported by the finding that raising the extracellular K⁺ concentration caused increased expression of c‐fos in a concentration‐dependent manner. Conclusion: The results suggest that in the absence of wall stress, ET‐1 is able to induce increased expression of c‐fos independent of traditional growth pathways, such as MAP kinase. The mechanism appears to be calcium‐dependent.