Protein tyrosine phosphatase inhibitor, orthovanadate, induces vasoconstriction and vasorelaxation in mouse thoracic aortas

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Background: Orthovanadate (OVA), a protein tyrosine phosphatase inhibitor, induced vasoconstriction in rat thoracic aortas and mesenteric arteries, which was abolished by Src, epidermal growth factor (EGF) receptor (EGFR), extracellular signal-regulated kinases 1 and 2 (Erk1/2), Erk1/2 kinase (MEK), and Rho kinase inhibitors. Furthermore, metalloproteinase inhibitor and an inhibitor of heparin/EGF binding attenuated OVA-induced constriction in the rat thoracic aortas, but not in mesenteric arteries. On the contrary, endothelium-dependent vasodilation was evoked by vanadate in rat mesenteric arteries, which was abolished by the nitric oxide (NO) synthase (NOS) inhibitor. However, the effect of OVA on mouse thoracic aortas is unknown. The objective of this study was to determine the role of OVA to vasoreaction in mouse thoracic aortas.

Methods: The thoracic aortas of male ddY mice were excised and cut into rings, and the endothelium of some rings was removed. Each ring was fixed vertically in organ bath filled with Krebs-Henseleit solution. OVA was cumulatively added to a final concentration of between 31.3 - 500 μM. The inhibitors were added 15 min prior to OVA. Phosphorylation levels of myosin phosphatase target subunit 1 (MYPT1), Src, Erk, p38, and c-Jun N-terminal kinase (JNK) were measured by western blotting.

Results: OVA produced relaxation response, which was significantly blocked by the phosphoinositide 3-kinase (PI3K), NOS, and the Src inhibitors. OVA-induced constriction of endothelium-denuded aortic rings was significantly blocked by Rho kinase, Erk1/2, MEK, EGFR, and Src inhibitors, and was partially blocked by JNK and p38 inhibitors. Phosphorylation of MYPT1 was abrogated by inhibitors of Src, EGFR, MEK, Erk1/2, and Rho kinase, but not by inhibitors of JNK and p38. OVA-stimulated Erk1/2 phosphorylation was blocked by inhibitors of EGFR, Src, MEK, and Erk1/2, whereas the Rho kinase inhibitor did not affect OVA-induced Erk1/2 phosphorylation. In addition, OVA increased the phosphorylation of Src in mouse thoracic aortas, which was blocked in the presence of Src inhibitor.

Conclusions: OVA-induced relaxation is regulated by NO via PI3K and NOS activation. Conversely, OVA induces vasoconstriction in mouse thoracic aortas via Src, EGFR, MEK, and Erk1/2 activation, leading to inactivation of myosin light chain phosphatase via MYPT1 phosphorylation.