Norepinephrine Stimulates Mitogen-Activated Protein Kinase Activity in GT1–1 Gonadotropin-Releasing Hormone Neuronal Cell Lines

The GT1–1 GnRH neuronal cell lines exhibit highly differentiated properties of GnRH neurons. We have used GT1–1 cells to study the roles of norepinephrine (NE), membrane depolarization, calcium influx, and phorbol esters in the regulation of mitogen-activated protein (MAP) kinase. NE, which is known to stimulate the release of GnRH, induced MAP kinase activity, the tyrosine phosphorylation of MAP kinase, and MAP kinase kinase activity. Forskolin led to activation of MAP kinase comparable with that induced by NE, and a selective inhibitor of cAMP-dependent protein kinase, H8, attenuated the NE-induced activation of MAP kinase. On the other hand, elimination of extracellular calcium by EGTA completely blocked NE-induced tyrosine phosphorylation of MAP kinase, and a selective inhibitor of calcium/calmodulin-dependent protein kinase, KN-62, attenuated the NE-induced activation of MAP kinase. Furthermore, depolarization of GT1–1 cells with 75 mm KCl, 10 μm BayK 8644, or 1μ m calcium ionophore (A23187) induced ...