SEROTONIN ACTIVATES THE MITOGEN-ACTIVATED PROTEIN-KINASE PATHWAY IN VASCULAR SMOOTH-MUSCLE - USE OF THE MITOGEN-ACTIVATED PROTEIN-KINASE KINASE INHIBITOR PD098059

Serotonin (5-hydroxytryptamine, 5-HT) promotes changes in vascular smo oth muscle contractility and is a vascular smooth muscle mitogen. The hypothesis that 5-HT-induced arterial contraction is partially depende nt on tyrosine kinase activation was tested in this study. Specificall y, we examined the role of the tyrosine kinase mitogen-activated prote in kinase kinase in 5-HT-induced vascular contraction by using a novel inhibitor of mitogen-activated protein kinase kinase PD098059. Helica l strips of rat aorta, mesenteric and tail artery denuded of endotheli um were mounted in tissue baths for measurement of isometric contracti le force. 5-HT-induced contraction in all arteries was mediated by 5-H T2A receptors as ketanserin (3-30 nM) was a competitive antagonist in all arteries (pK(B) = 8.58-8.96). Genistein (5 x 10(-6) M) and tyrphos tinB42 (3 x 10(-5) M), two unrelated tyrosine kinase inhibitors, shift ed 5-HT-induced contraction toward the right in all arteries (approxim ately eightfold). By contrast, daidzein (5 x 10(-6) M), the inactive i somer of genistein, did not reduce contraction to 5-HT in any artery. These findings suggest that 5-HT-induced activation of tyrosine kinase (s) may be a signal transduction pathway used by vascular 5-HT2A recep tors. PD098059 (1 x 10(-5) M) reduced contraction to 5-HT in all arter ies, indicating that 1) the tyrosine kinase(s) inhibited by genistein and tyrphostin42 probably include mitogen-activated protein kinase kin ase and 2) activation of MEK is important for 5-HT-induced contraction . Western analyses of aortic strips contracted to 5-HT (10(-6) M) indi cates that tyrosyl-phosphorylation of the mitogen activated protein ki nases Erk-1 and Erk-2 was increased (approximately 200% and 15% of bas al levels, respectively) and PD098059 (1 x 10(-5) M) significantly red uced 5-HT-stimulated tyrosyl-phosphorylation of Erk-1. Thus, these dat a support the use of the mitogen-activated protein kinase pathway by 5 -HT in causing arterial contraction and demonstrates the usefulness of specific inhibition of the mitogen-activated protein kinase pathway.