Involvement of BKCa alpha subunit tyrosine phosphorylation in vascular hyporesponsiveness of superior mesenteric artery following hemorrhagic shock in rats.

OBJECTIVE

Vascular hyporesponsiveness is a major complication following severe trauma and shock. It plays important roles in the development of shock and seriously interferes with the treatment of shock. The mechanism responsible for the occurrence of vascular hyporesponsiveness has not been fully understood. The purpose of this study was to determine whether the alpha subunit tyrosine sites of large conductance calcium-activated potassium channel (BK(Ca)) could be phosphorylated and whether the phosphorylation of BK(Ca) was closely associated with the activation of BK(Ca) and the development of vascular hyporesponsiveness following hemorrhagic shock in rats.

METHODS

A hemorrhagic shock (30 mm Hg for 0.5, 2, 4 h) model of Wistar rats was established. Phosphorylation of tyrosine residues of the BK(Ca) alpha subunit from vascular smooth muscle cells (VSMC) in superior mesenteric arteries (SMA) was detected by immunoprecipitation and Western blotting. BK(Ca) activity was evaluated by cell-attached patch clamping. The vascular responsiveness of SMA to norepinephrine was measured with an isolated organ perfusion system.

RESULTS

The level of BK(Ca) alpha subunit tyrosine phosphorylation was increased in a time-dependent manner following hemorrhagic shock, which was mediated by protein tyrosine kinases (PTK) and protein tyrosine phosphatases (PTP). The activation of VSMC BK(Ca) following hemorrhagic shock was inhibited by genistein (2x10(-5) mol/L), the permeable isoflavone PTK inhibitor, and was potentiated by the PTP inhibitor sodium orthovanadate (Na(3)VO(4), 10(-3) mol/L). The decreased vasoresponsiveness following hemorrhagic shock was partly restored by genistein (10(-5) mol/L) or by the BK(Ca)-selective inhibitor tetrabutylammonium chloride (0.1 mmol/L), while it was further decreased by Na(3)VO(4) (10(-5) mol/L).

CONCLUSIONS

The tyrosine residues of BK(Ca) alpha subunit of SMA were phosphorylated following hemorrhagic shock, which was regulated by PTK and PTP and appeared to be related to the activation of BK(Ca) and the development of vascular hyporesponsiveness following hemorrhagic shock.