Rabu, 29 Februari 2012

Calcium-independent phospholipase A2 participates in KCl-induced calcium sensitization of vascular smooth muscle

Paul H. Ratz1,2 ,*, Amy S. Miner1,2, and Suzanne E. Barbour1
1Department of Biochemistry and Molecular Biology, Virginia Commonwealth University School of Medicine, USA
2Department of Pediatrics, Virginia Commonwealth University School of Medicine, USA


Abstract
In vascular smooth muscle, KCl elevates intracellular free Ca2+ ([Ca2+]i), myosin light chain kinase activity and tension (T), but also can inhibit myosin light chain phosphatase activity by activation of rhoA kinase (ROCK), resulting in Ca2+ sensitization (increased T/[Ca2+]i ratio). Precisely how KCl causes ROCK-dependent Ca2+ sensitization remains to be determined. Using fura-2-loaded isometric rings of rabbit artery, we found that the Ca2+-independent phospholipase A2 (iPLA2) inhibitor, bromoenol lactone (BEL), reduced the KCl-induced tonic but not early phasic phase of T and potentiated [Ca2+]i, reducing Ca2+ sensitization. The PKC inhibitor, GF-109203X (3μM) and the pseudosubstrate inhibitor of PKCζ produced a response similar to BEL. BEL reduced basal and KClstimulated myosin phosphatase phosphorylation. Whereas BEL and H-1152 produced strong inhibition of KCl-induced tonic T (~50%), H-1152 did not induce additional inhibition of tissues already inhibited by BEL, suggesting that iPLA2 links KCl stimulation with ROCK activation. The cPLA2 inhibitor, pyrrolidine-1, inhibited KCl-induced tonic increases in [Ca2+]i but not T, whereas the inhibitor of 20-HETE production, HET0016, acted like the ROCK inhibitor H-1152 by causing Ca2+ desensitization. These data support a model in which iPLA2 activity regulates Ca2+ sensitivity.

Keywords : vascular smooth muscle; rabbit artery; contraction; K+-depolarization; Ca2+ signaling; fura-2; signal transduction; Ca2+ sensitization; Rho-kinase; PLA2; BEL; ETYA; NDGA; HET0016; H-1152; HA-1077; Y-27632; 20-HETE; pyrrolidine-1; GF-109203X; PKC pseudosubstrate inhibitor.

Sumber : Cell Calcium. 2009 July ; 46(1): 65–72. doi:10.1016/j.ceca.2009.05.001.
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