Activation of Erk mitogen-activated protein kinase proteins by vascular serotonin receptors

We previously demonstrated that 5-hydroxytryptamine 2A (5-HT2A) receptor-mediated rat arterial contraction was dependent on activation of tyrosine kinases, including mitogen-activated protein kinase (MAPK) kinase. In the current study, we examined arterial smooth muscle for the presence of serotonin (5-hydroxytryptamine, 5-HT) 5-HT1B, 5-HT1D, 5-HT1F, 5-HT2A, 5-HT2B, and 5-HT7 receptor mRNA and hypothesized that, if present, activation of these receptors would stimulate the extracellular signal-regulated kinase (Erk) MAPK pathway and an Erk MAPK-dependent contraction. RT-PCR analyses of rat aortic smooth muscle cells, cultured and fresh, indicated the presence of 5-HT1B, 5-HT1D, 5-HT1F, 5-HT2A, 5-HT2B, and 5-HT7 receptor mRNA. The 5-HT1B agonists RU24969 and CGS 12066B, 5-HT1B/1D/1F receptor agonist sumatriptan, and 5-HT2B receptor agonist BW723C86 (10(-9) 10(-4) M) did not contract the aorta, nor did the 5-HT7 receptor antagonist LY215840 leftward shift 5-HT-induced contraction. The 5-HT1E/1F receptor agonist BRL54443 induced contraction, but this was abolished by the 5-HT2A/2C receptor antagonist ketanserin (10 nM); contraction was not observed with a different 5-HT1F receptor agonist, LY344864. 5-HT and alpha -methyl-5-HT produced a concentration-dependent increase in Erk MAPK activity in cultured aortic smooth muscle cells and in aorta contracted with these agonists. All other agonists were inactive; a high concentration of BRL54443 (10 muM) stimulated Erk MAPK activation (150% basal). Thus, while mRNA and possibly protein for multiple 5-HT receptors are present in aortic smooth muscle, only the 5-HT2A receptor plays a significant role in directly modulating contractility and activating the Erk MAPK pathway.