title: Intermittent hypoxia in rats increases myogenic tone through loss of hydrogen sulfide activation of large-conductance Ca(2+)-activated potassium channels.
abstract: BACKGROUND
  Myogenic tone, an important regulator of vascular resistance, is dependent on vascular smooth muscle (VSM) depolarization, can be modulated by endothelial factors, and is increased in several models of hypertension. Intermittent hypoxia (IH) elevates blood pressure and causes endothelial dysfunction. Hydrogen sulfide (H(2)S), a recently described endothelium-derived vasodilator, is produced by the enzyme cystathionine γ-lyase (CSE) and acts by hyperpolarizing VSM.
  
  
  OBJECTIVE
  Determine whether IH decreases endothelial H(2)S production to increase myogenic tone in small mesenteric arteries.
  
  
  RESULTS
  Myogenic tone was greater in mesenteric arteries from IH than sham control rat arteries, and VSM membrane potential was depolarized in IH in comparison with sham arteries. Endothelium inactivation or scavenging of H(2)S enhanced myogenic tone in sham arteries to the level of IH. Inhibiting CSE also enhanced myogenic tone and depolarized VSM in sham but not IH arteries. Similar results were seen in cerebral arteries. Exogenous H(2)S dilated and hyperpolarized sham and IH arteries, and this dilation was blocked by iberiotoxin, paxilline, and KCl preconstriction but not glibenclamide or 3-isobutyl-1-methylxanthine. Iberiotoxin enhanced myogenic tone in both groups but more in sham than IH. CSE immunofluorescence was less in the endothelium of IH than in sham mesenteric arteries. Endogenouse H(2)S dilation was reduced in IH arteries.
  
  
  CONCLUSIONS
  IH appears to decrease endothelial CSE expression to reduce H(2)S production, depolarize VSM, and enhance myogenic tone. H(2)S dilatation and hyperpolarization of VSM in small mesenteric arteries requires BK(Ca) channels.
authors.affiliation: Vascular Physiology Group, Department of Cell Biology and Physiology, School of Medicine, University of New Mexico, Albuquerque, NM 87131, USA.
authors.forename: Olan
authors.initials: O
authors.lastname: Jackson-Weaver
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Paredes
authors.forename: Laura V
authors.initials: LV
authors.lastname: Gonzalez Bosc
authors.forename: Benjimen R
authors.initials: BR
authors.lastname: Walker
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Kanagy
mesh_terms: D015056:1-Methyl-3-isobutylxanthine; D000393:Air Pollutants / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004730:Endothelium, Vascular / Q000378:metabolism* / Q000473:pathology; D005905:Glyburide / Q000494:pharmacology; D006862:Hydrogen Sulfide / Q000378:metabolism / Q000494:pharmacology*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D000860:Hypoxia / Q000378:metabolism* / Q000503:physiopathology; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism*; D008297:Male; D008638:Mesenteric Arteries / Q000378:metabolism* / Q000473:pathology; D051419:Paxillin / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D000393:Air Pollutants; D007004:Hypoglycemic Agents; D051036:Large-Conductance Calcium-Activated Potassium Channels; D051419:Paxillin; D010455:Peptides; D010726:Phosphodiesterase Inhibitors; C064719:iberiotoxin; D005905:Glyburide; D015056:1-Methyl-3-isobutylxanthine; D006862:Hydrogen Sulfide