5-hydroxytryplamine stimulates phosphorylation of p44/p42 mitogen-activated protein kinase activation in bovine aortic endothelial cell cultures

5-Hydroxytryptamine (5-MT) is sequestered and released by endothelial cells, acts as an endothelial cell mitogen, promotes the release of nitric oxide (NO), and has been associated with the p44/p42 mitogen-activated protein kinase (MAPK) cascade. NO also acts as a cell mitogen and promotes signals that culminate in the phosphorylation of MAPK. The aim of this study was to test whether endothelial 5-HT receptors stimulate dual (tyrosyl- and threonyl-) phosphorylation of MAPK through a mitogen-activated protein kinase kinase-1 (MEK-1) and eNOS-dependent pathway in bovine aortic endothelial cells (BAECs). As shown by Western blot analysis, 5-HT and the 5-HT1B-selective agonist 5-nonyloxytryptamine (5-NOT) stimulate time- and concentration-dependent (0.001- 10 mu M) phosphorylation of MAPK in these cells. The agonist stimulated phosphorylation of MAPK was blocked by the 5-HT1B-receptor antagonist isamoltane (0.01-10 mu M) and the MEK-1 inhibitor PD 098059 {[2-(2'-amino-3 '-methoxyphenyl)-oxanaphthalen-4-one]; 0.01-10 mu<}. The eNOS inhibitor L-N-omega-iminoethyl-L-ornithine (L-NIO; 0.01-10 mu M) failed to block; the 1 mu M 5-NOT-stimulated responses. Our findings suggest that the 5-HT receptors (specifically 5-HT1B) mediate signals to MEK-1 and subsequently to MAPK through an eNOS-independent pathway in BAECs.