Characterization of the serotonin receptor mediating contraction in the mouse thoracic aorta and signal pathway coupling.

The purpose of this study was to characterize pharmacologically the 5-HT receptor(s) mediating contraction in the mouse aorta and the pathways these receptors are coupled with to mediate contraction. We hypothesized that a 5-HT2A receptor, as in the rat, mediates contraction by activating L-type calcium channels, phospholipase C (PLC), and tyrosine kinase(s). Endothelium-denuded aortic strips were placed in a tissue bath for measurement of isometric contractile force. 5-HT, the 5-HT2A receptor agonist alpha-methyl-5-HT, and partial 5-HT2A receptor agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (+/--DOI) caused the most potent and efficacious contraction. The 5-HT(1E/1F) receptor agonist BRL 54443 also induced contraction (-log EC(50) = 6.52); however, the 5-HT2A receptor antagonist ketanserin antagonized this contraction. Our hypothesis was further supported by the finding that antagonists with affinity for the 5-HT2A receptor, ketanserin, 1-(1-naphthyl)piperazine, spiperone, and LY53857, reduced 5-HT-induced contraction. A correlation of 0.927 was found between literature-derived compound binding affinities for the agonists and antagonists at the 5-HT2A receptor of the rat and the data generated in our experiments (-log EC(50) and pK(B) values). The L-type calcium channel blockers nifedipine and nitrendipine, PLC inhibitor 2-nitro-4-carboxyphenyl N,N-diphenylcarbamate, and tyrosine kinase inhibitors genistein and PD 098,059 all shifted and/or reduced maximum contraction to 5-HT. We conclude that contraction to 5-HT in the mouse aorta is mediated primarily by a 5-HT2A receptor and is coupled to L-type calcium channels, PLC, and tyrosine kinases.