We have previously reported the Ras-dependent activation of the mitogen-activated protein kinases p44 and p42, also termed extracellular signal-regulated kinases (ERK)1 and 2 (ERK1⁄2), mediated through Gs-coupled serotonin receptors transiently expressed in human embryonic kidney (HEK) 293 cells. Whereas G i- and Gq-coupled receptors have been shown to activate Ras through the guanine nucleotide exchange factor (GEF) called Ras-GRF1 (CDC25 Mm ) by binding of Ca 2+ ⁄calmodulin to its N-terminal IQ domain, .
