Calcium-independent phospholipase A2 participates in KCl-induced calcium sensitization of vascular smooth muscle.
In vascular smooth muscle, KCl not only elevates intracellular free Ca(2+) ([Ca(2+)](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(2+) sensitization (increased T/[Ca(2+)](i) ratio). Precisely how KCl causes ROCK-dependent Ca(2+) sensitization remains to be determined. Using Fura-2-loaded isometric rings of rabbit artery, we found that the Ca(2+)-independent phospholipase A(2) (iPLA(2)) inhibitor, bromoenol lactone (BEL), reduced the KCl-induced tonic but not early phasic phase of T and potentiated [Ca(2+)](i), reducing Ca(2+) sensitization. The PKC inhibitor, GF-109203X (> or =3 microM) and the pseudo-substrate inhibitor of PKCzeta 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 (approximately 50%), H-1152 did not induce additional inhibition of tissues already inhibited by BEL, suggesting that iPLA(2) links KCl stimulation with ROCK activation. The cPLA(2) inhibitor, pyrrolidine-1, inhibited KCl-induced tonic increases in [Ca(2+)](i) but not T, whereas the inhibitor of 20-HETE production, HET0016, acted like the ROCK inhibitor H-1152 by causing Ca(2+) desensitization. These data support a model in which iPLA(2) activity regulates Ca(2+) sensitivity.
Ratz
Paul H
PH
Department of Biochemistry and Molecular Biology, Virginia Commonwealth University School of Medicine, USA. phratz@vcu.edu
Miner
Amy S
AS
Barbour
Suzanne E
SE
D015117:5,8,11,14-Eicosatetraynoic Acid / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000037:antagonists & inhibitors; D002118:Calcium / Q000378:metabolism*; D007700:Kinetics; D009119:Muscle Contraction / Q000187:drug effects; D009129:Muscle Tonus / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D009281:Naphthalenes / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D054512:Phospholipases A2, Calcium-Independent / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011753:Pyrones / Q000494:pharmacology; D011759:Pyrrolidines / Q000494:pharmacology; D011817:Rabbits; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors; D000099221:Protein Kinase C zeta
D015117:5,8,11,14-Eicosatetraynoic Acid; D016718:Arachidonic Acid; D002118:Calcium; D009219:Myosin-Light-Chain Kinase; D009281:Naphthalenes; D010656:Phenylephrine; D054512:Phospholipases A2, Calcium-Independent; D011189:Potassium Chloride; D011493:Protein Kinase C; D011753:Pyrones; D011759:Pyrrolidines; D054460:rho-Associated Kinases; D000099221:Protein Kinase C zeta; C068314:6-(bromomethylene)tetrahydro-3-(1-naphthaleneyl)-2H-pyran-2-one; C032519:pyrrolidine