Calcium-independent phospholipase A sub(2) participates in KCl-induced calcium sensitization of vascular smooth muscle

• Published in: Cell calcium (Edinburgh) 2009-07, Vol.46 (1), p.65-72
• Main Authors: Ratz, PH, Miner, A S, Barbour, SE
• Format: Article
• Language: English
• ISSN: 0143-4160
• DOI: 10.1016/j.ceca.2009.05.001

In vascular smooth muscle, KCl not only elevates intracellular free Ca super(2) super(+) ([Ca super(2) super(+)] sub(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 Ca super(2) super(+) sensitization (increased T/[Ca super(2) super(+)] sub(i) ratio). Precisely how KCl causes ROCK-dependent Ca super(2) super(+) sensitization remains to be determined. Using Fura-2-loaded isometric rings of rabbit artery, we found that the Ca super(2) super(+)-independent phospholipase A sub(2) (iPLA sub(2)) inhibitor, bromoenol lactone (BEL), reduced the KCl-induced tonic but not early phasic phase of T and potentiated [Ca super(2) super(+)] sub(i), reducing Ca super(2) super(+) sensitization. The PKC inhibitor, GF-109203X (>=3 mu M) and the pseudo-substrate inhibitor of PKC direct sum produced a response similar to BEL. BEL reduced basal and KCl-stimulated 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 iPLA sub(2) links KCl stimulation with ROCK activation. The cPLA sub(2) inhibitor, pyrrolidine-1, inhibited KCl-induced tonic increases in [Ca super(2) super(+)] sub(i) but not T, whereas the inhibitor of 20-HETE production, HET0016, acted like the ROCK inhibitor H-1152 by causing Ca super(2) super(+) desensitization. These data support a model in which iPLA sub(2) activity regulates Ca super(2) super(+) sensitivity.