title: Acidosis-induced relaxation of human internal mammary artery is due to activation of ATP-sensitive potassium channels.
abstract: Metabolic acidosis is associated with various clinical situations including diabetes mellitus and renal diseases. The aim of this study was to investigate the effects of acidosis on the resting as well as precontracted human left internal mammary artery. The vessels were obtained from the patients undergoing coronary artery bypass grafting surgery at The Aga Khan University Hospital, Karachi. Left internal mammary artery was cut into rings and isometric tension recording experiments were performed. Decrease in pH of the bathing solution from 7.4 to 6.8 had no effect on the resting tension of left internal mammary artery, whereas, acidic pH markedly relaxed the contractions to 24.8 mM KCl and 300 nM phenylephrine. Interestingly, when the KCl- or phenylephrine-contracted rings were treated with 3 microM glibenclamide; an inhibitor of ATP-sensitive potassium (K(ATP)) channels, the relaxant effect of acidosis was abolished. Similarly, acidosis failed to cause relaxation of 100 nM endothelin-1-induced contraction in Ca2+-free bathing solution or in the presence of a voltage-dependent Ca2+ channel inhibitor, verapamil (10 microM), whereas, endothelin-1-induced contraction was attenuated by acidosis in Ca2+-containing normal solution. From all these data, it is concluded that under the acidic pH conditions, opening of K(ATP) channels occurs; resulting in the hyperpolarization, decrease in Ca2+ influx via voltage-dependent Ca2+ channels and subsequent relaxation of human left internal mammary artery.
authors.affiliation: Department of Biological and Biomedical Sciences, Faculty of Health Sciences, The Aga Khan University, Stadium Road, P.O. Box 3500, Karachi 74800, Pakistan. dileep.rohra@aku.edu
authors.forename: Dileep Kumar
authors.initials: DK
authors.lastname: Rohra
authors.forename: Hasanat Mohammad
authors.initials: HM
authors.lastname: Sharif
authors.forename: Hina Saeed
authors.initials: HS
authors.lastname: Zubairi
authors.forename: Kiran
authors.initials: K
authors.lastname: Sarfraz
authors.forename: Muhammad Nabeel
authors.initials: MN
authors.lastname: Ghayur
authors.forename: Anwarul Hassan
authors.initials: AH
authors.lastname: Gilani
mesh_terms: D000138:Acidosis / Q000503:physiopathology*; D000255:Adenosine Triphosphate / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008323:Mammary Arteries / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: D015221:Potassium Channels; D014665:Vasodilator Agents; D000255:Adenosine Triphosphate; D014700:Verapamil; D005905:Glyburide; D002118:Calcium