Abstract 2638: Potentiation of Endothelin-1-induced Ca 2+ Sensitization of Myofilament after Subarachnoid Hemorrhage

Abstract

Introduction: Increased vascular reactiveness in response to endothelin-1 (ET-1) plays an important role in the development of cerebral vasospasm. We elucidated some mechanisms of the increased vascular reactiveness to ET-1 using the basilar artery in a rabbit subarachnoid hemorrhage (SAH) model. Material & Methods: The contractile response and the expression of regulatory protein of the isolated basilar artery were evaluated. Results: ET-1 induced greater contraction than other agonists or 118 mM K + depolarization for the extent of [Ca 2+ ] i elevation, suggesting that myofilament Ca 2+ sensitivity is a greater contributor to ET-1-induced contractions than other contractions. ET-1-induced contraction of α-toxin-permeabilized strips was significantly enhanced and sustained in SAH compared to control, suggesting that the ET-1-induced myofilament Ca 2+ sensitization was potentiated after SAH. Therefore, we investigated the intracellular signaling pathway involving Rho-associated coiled-coil protein kinase (ROCK) and protein kinase C (PKC), which are two major signaling molecules that contribute to myofilament Ca 2+ sensitization. ET-1-induced contraction of α-toxin-permeabilized control strips was blocked by inhibitors to ROCK and PKC in a concentration-dependent manner, whereas the concentration-response curve shifted to the right in SAH, suggesting that ET-1-induced myofilament Ca 2+ sensitization became less sensitive to inhibitors of ROCK and PKC after SAH. The expression of PKCα, ROCK2, PKC - potentiated phosphatase inhibitor of 17 kDa (CPI-17), and myosin phosphatase target subunit 1 (MYPT1) was upregulated and the level of phosphorylation of MYPT-1 at T853, and CPI-17 at T38 was increased after SAH. ET-1 induced an enhanced and sustained elevation of the phosphorylation of MYPT1 at both T696 and T853 after SAH. Conclusion: Ca 2+ -sensitizing effect of ET-1 on myofilaments was enhanced and prolonged after SAH. The increased expression and activity of PKCα, ROCK2, CPI-17, and MYPT1 are suggested to underlie the enhanced and prolonged Ca 2+ -sensitization. ET-1-induced potentiation of myofilament Ca 2+ sensitization may cause an increased vascular reactiveness in response to ET-1 after SAH, leading to the development of cerebral vasospasm.