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October 17, 2009
9:00 AM - 11:00 AM
Room Area E
Volatile Anesthetics Inhibit KCl-Induced, PI3K-C2a-Mediated, MLC Phosphorylation in Rat Aortic VSM
  **   Feng Qi, M.D., Ogawa Koji, M.D., Tokinaga Yasuyuki, M.D., Uematsu Nobuhiko, M.D., Hatano Yoshio, M.D.
Department of Anesthesiology, Wakayama Medical University, Wakayama City, Wakayama, Japan
Background: Vascular contraction is regulated by the balance of the activity between myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP). Inhibition of MLCP leads to MLC phosphorylation and contraction for a given intracellular Ca 2+ concentration ([Ca 2+ ] i ), and results in promoting myofilament Ca 2+ sensitivity. Available evidence suggests that Class II phosphoinositide 3-kinase a-isoform (PI3K-C2α) can regulate Rho activity that inhibits myosin phosphatase, resulting vascular contraction. We previously demonstrated that sevoflurane inhibits guanosine 5'-[γ-thio]triphosphate (GTPγS)-stimulated Rho/ Rho kinase-mediated contraction of rat aortic smooth muscle, and that isoflurane suppressed angiotensin II-induced MLCP regulated subunit, MYPT1/Thr853-mediated Ca 2+ sensitization. These findings suggest that Rho-Rho kinase pathway might be target site of action of anesthetics. The current study was designed to investigate the sevoflurane and isoflurane on PI3K- and Rho kinase-mediated MLC phosphorylation in response to KCl in rat aortic smooth muscle.

Methods : With institutional approval, endothelium-denuded rat aortic strips were isolated. Class I PI3K,PI3K-C2α and Rho kinase membrane translocation, MLC phosphorylation in response to KCl (60mM), in the absence or presence of sevoflurane (1.7% and 3.4%), isoflurane (1.2% and 2.3%), PI3K inhibitor LY294002 (10 -5 M, or 10 -3 M), or Rho kinase inhibitor Y27632 (10 -6 M) were measured, using Western blotting analysis.

Results : Membrane depolarization by KCl (60mM) induced the membrane translocation of PI3K and Rho kinase (Rock 2) and subsequently increased MLC phosphorylation in rat denuded VSM strips. These activations of PI3K, Rho kinase and MLC were reversed by either LY294002 or Y27632. Both sevoflurane and isoflurane inhibited the MLC phosphorylation and the membrane translocation of Rho kinase and PI3K-C2α, but not of Class I PI3K in response to KCl in a concentration-dependent manner.[figure1] Conclusion : Both sevoflurane and isoflurane inhibit KCl-induced MLC phosphorylation by modulating PI3K-C2α and Rho kinase activity in rat vascular smooth muscle. PI3K-C2α isoform and Rho kinase may be the common target sites of action of these anesthetics in the intracellular signaling pathway that regulates vascular smooth muscle contraction.

From Proceedings of the 2009 Annual Meeting of the American Society Anesthesiologists.
Figure 1