Effect of nitric oxide-induced tyrosine phosphorylation of calcium-activated potassium channel α subunit on vascular hyporesponsiveness in rats

Objective: To study the effect of nitric oxide-induced tyrosine phosphorylation of large-conductance calcium-activated potassium (BK Ca) channel α subunit on vascular hyporesponsiveness in rats. Methods: A total of 46 Wistar rats of either sex, weighing 250 g±20 g, were used in this study. Models of vascular hyporesponsiveness induced by hemorrhagic shock (30 mm Hg for 2 hours) in vivo and by L-arginine in vitro were established respectively. The vascular responsiveness of isolated superior mesenteric arteries to norepinephrine was observed. Tyrosine phosphorylation of BK Ca α subunit was evaluated with methods of immunoprecipitation and Western blotting. Results: In the smooth muscle cells of the superior mesenteric arteries, the expression of BK Ca α subunit tyrosine phosphorylation increased following hemorrhagic shock, and L-arginine could induce BK Ca channel α subunit tyrosine phosphorylation in a time- and dose-dependent manner. L-NAME (Nω-nitro-L-arginine-methyl-ester), a nitric oxide synthetase inhibitor, could partly restore the decreased vasoresponsiveness of the superior mesenteric arteries after hemorrhagic shock in rats. Down-regulating the protein tyrosine phosphorylation with genistein, a widely-used special protein tyrosine kinase inhibitor, could partly improve the decreased vasoresponsiveness of the superior mesenteric arteries induced by L-arginine in vitro, while up-regulating the protein tyrosine phosphorylation with Na3VO4, a protein tyrosine phosphatase inhibitor, could further decrease the nitric oxide-induced vascular hyporesponsiveness, which could be partly ameliorated by 0.1 mmol/L tetrabutylammonium chloride (TEA), a selective BK Ca inhibitor at this concentration. Conclusions: Nitric oxide can induce the tyrosine phosphorylation of BK Ca α subunit, which influences the vascular hyporesponsiveness in hemorrhagic shock rats or induced by L-arginine in vitro.

Prostacyclin decreases splanchnic vascular contractility in cirrhotic rats

BACKGROUND： Prostacyclin has been shown to increase portal hypertension, but the mechanism is unclear. This study aimed to investigate whether the overproduction of prostacyclin（PGI2） in cirrhosis participates in the splanchnic vascular hyporesponsiveness to vasoconstrictors in cirrhotic rats.METHODS： Cirrhotic model was created by subcutaneous injection of 60% carbon tetrachloride（CCl4） corn oil solution combined with intermittent drinking of 5% alcohol, and agematched rats served as controls. The isolated third-generation mesenteric arterioles were used to examine the contractile response to norepinephrine. The changes in vascular diameter were observed under a microscope imaging device. The plasma concentration of 6-ketone-prostaglandin F1α（6-keto-PGF1α, a stable metabolite of PGI2） was tested via enzyme immunoassays and the expression of cyclooxygenase（COX） in mesenteric arteries was detected by Western blotting.RESULTS： In parallel with the increase of plasma 6-ketoPGF1α, the contractile response of arterioles from cirrhotic rats to norepinephrine was significantly impaired compared with that from controls. Inhibition of PGI2 or protein kinase A with indomethacin or Rp-adenosine 3＇, 5＇-cyclic monophosphothioate（Rp-cAMPS） partially reversed the vascular hypo-contractile response to norepinephrine in arterioles from cirrhotic rats.Indomethacin significantly decreased the plasma 6-keto-PGF1α.Furthermore, indomethacin significantly attenuated the effect of Rp-cAMPS on arterioles from cirrhotic rats. COX-1 expression was up-regulated in mesenteric arteries from cirrhotic rats,whereas COX-2 was not detectable in the mesenteric arteries from both cirrhotic and control rats.CONCLUSION： Enhanced COX-1 expression in cirrhotic rats resulted in elevated PGI2 production which partially contributedto the splanchnic vascular hyporesponsiveness to a vasoconstrictor via the protein kinase A pathway.