The role of calcium desensitization in vascular hyporeactivity and its regulation after hemorrhagic shock in the rat

The objectives of the present study were to investigate the role of calcium desensitization in vascular hyporeactivity, and the regulatory effects of Rho-kinase, protein kinase C (PKC), and protein kinase G (PKG) on calcium sensitivity. The vascular reactivity and calcium sensitivity with superior mesenteric artery (SMA) from hemorrhagic shock rat were observed by measuring the contraction initiated by norepinephrine (NE) and Ca2+ under depolarizing conditions (120 mmol/L K) in an isolated organ perfusion system. Angiotensin II (Ang-II) and Fasudil, the Rho-kinase agonist and inhibitor, phorbol 12-myristate 13-acetate (PMA) and staurosporine, the PKC agonist and inhibitor, 8Br-cGMP and KT-5823, the PKG agonist and inhibitor, and Calyculin A, myosin light chain phosphatase (MLCP) inhibitor were used as tool agents. The results indicated that vascular reactivity and calcium sensitivity were decreased after hemorrhagic shock. The cumulative dose-response curve of SMA to NE and Ca2+ after shock was shifted to the right. Ang-II (10 mol/L) could improve the decreased vascular reactivity by increasing the calcium sensitivity of SMA, and insulin (100 nmol/L) could further decrease the vascular reactivity by decreasing the calcium sensitivity of SMA. These results suggested that the vasculature after shock was desensitized to calcium, which played an important role in the onset of vascular hyporeactivity after shock. PMA and KT-5823 could increase the sensitivity of SMA to Ca2+ and made the cumulative dose-response curve shift to the left. In contrast, Fasudil, staurosporine, and 8Br-cGMP decreased the sensitivity of SMA to Ca2+ and made the cumulative dose-response curve of Ca2+ shift to the right. Calyculin A (10 mol/L) pretreatment further enhanced Ang-II, and PMA induced increase of calcium sensitivity, yet weakened the 8Br-cGMP-induced decrease of calcium sensitivity. Taken together, the data suggest that Rho-kinase, PKC, and PKG are involved in the regulation of calcium sensitivity of vascular smooth muscle after hemorrhagic shock, and their regulatory effects on calcium sensitivity of vasculature are possibly related to MLCP.