title: Matrix metalloproteinase 2-induced venous dilation via hyperpolarization and activation of K+ channels: relevance to varicose vein formation.
abstract: BACKGROUND
  Varicose veins are a common disorder of extensive venous dilation and remodeling with an as-yet unclear mechanism. Studies have shown increased plasma and tissue levels of matrix metalloproteinases (MMPs) in human varicose veins and animal models of venous hypertension. Although the effects of MMPs are generally attributed to extracellular matrix degradation, their effects on the mechanisms of venous contraction/relaxation are unclear. Our preliminary experiments have demonstrated that MMP-2 causes inhibition of phenylephrine-induced venous contraction. The purpose of this study was to determine whether MMP-induced inhibition of venous contraction involves an endothelium-dependent and/or -independent pathway.
  
  
  METHODS
  Circular segments of the inferior vena cava (IVC) were isolated from male Sprague-Dawley rats and suspended between two wire hooks in a tissue bath, and the effects of MMP-2 on phenylephrine- and KCl-induced contraction were measured. To study the role of endothelium-derived vasodilators, experiments were performed in the presence and absence of endothelium; N(G)-l-nitro-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthesis; indomethacin, an inhibitor of prostacyclin synthesis; cromakalim, an activator of adenosine triphosphate-sensitive K+ channels (K(ATP)); and iberiotoxin, a blocker of large-conductance Ca2+-dependent K+ channels (BK(Ca)) and smooth muscle hyperpolarization.
  
  
  RESULTS
  In endothelium-intact IVC segments, phenylephrine (10(-5) mol/L) caused significant contraction that slowly declined to 82.0% in 30 minutes. The addition of MMP-2 (1 microg/mL) caused a gradual decrease of phenylephrine contraction to 39.5% at 30 minutes. In endothelium-denuded IVC, MMP-2 induced a greater reduction of phenylephrine contraction, to 7.6%. In the presence of L-NAME (10(-4) mol/L), MMP-2 caused a marked decrease in phenylephrine contraction, to 4.4%. Large MMP-2-induced inhibition of phenylephrine contraction was also observed in IVC treated with L-NAME plus indomethacin. MMP-2 caused relaxation of phenylephrine contraction in IVC pretreated with cromakalim (10(-7) mol/L), an activator of K(ATP) channels. MMP-2-induced inhibition of phenylephrine contraction was abrogated in the presence of iberiotoxin (10(-8) mol/L), a blocker of BK(Ca). MMP-2 did not inhibit venous contraction during membrane depolarization by 96 mmol/L KCl, a condition that prevents outward K+ conductance and cell hyperpolarization.
  
  
  CONCLUSIONS
  MMP-2 causes significant IVC relaxation that is potentiated in the absence of endothelium or during blockade of endothelium-mediated nitric oxide and prostacyclin synthesis. The lack of effects of MMP-2 on KCl contraction and in iberiotoxin-treated veins suggests MMP-2-induced smooth muscle hyperpolarization and activation of BK(Ca) channels--a novel effect of MMP that may play a role in the early stages of venous dilation and varicose vein formation.
authors.affiliation: VA Boston Healthcare System, West Roxbury, MA, USA.
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Raffetto
authors.forename: Reagan L
authors.initials: RL
authors.lastname: Ross
authors.forename: Raouf A
authors.initials: RA
authors.lastname: Khalil
mesh_terms: D000818:Animals; D019806:Cromakalim / Q000494:pharmacology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004108:Dilatation, Pathologic; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D011464:Epoprostenol / Q000378:metabolism; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D008297:Male; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism* / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D010455:Peptides / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D014648:Varicose Veins / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects; D014665:Vasodilator Agents / Q000378:metabolism* / Q000494:pharmacology; D014682:Vena Cava, Inferior / Q000378:metabolism
chemical_list: D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; C494842:Kcnma1 protein, rat; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D010455:Peptides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D019806:Cromakalim; D010656:Phenylephrine; D009569:Nitric Oxide; D011189:Potassium Chloride; C064719:iberiotoxin; D011464:Epoprostenol; D019001:Nitric Oxide Synthase; D020778:Matrix Metalloproteinase 2; D019331:NG-Nitroarginine Methyl Ester; D007213:Indomethacin