title: Modulation by homocysteine of the iberiotoxin-sensitive, Ca2+ -activated K+ channels of porcine coronary artery smooth muscle cells.
abstract: We evaluated the acute effect of homocysteine on the iberiotoxin-sensitive, Ca(2+)-activated K(+) (BK(Ca)) channels of the porcine coronary artery smooth muscle cells. NS 1619 (1 to 30 microM) caused a concentration-dependent enhancement of the BK(Ca) amplitude (recorded using the whole-cell, membrane-rupture configuration) only with an elevated [Ca(2+)](i) of approximately 444 nM, but not with [Ca(2+)](i) of approximately 100 nM. Homocysteine (30 microM) caused a small inhibition ( approximately 16%) of the BK(Ca) amplitude ([Ca(2+)](i)= approximately 444 nM), and a greater inhibition ( approximately 77%) was observed with 100 microM NADH present in the pipette solution. The inhibition persisted after washing. With NADPH (100 microM), a smaller magnitude of inhibition ( approximately 34%) of the BK(Ca) amplitude was recorded. The NS 1619-mediated enhancement of the BK(Ca) amplitude (with elevated [Ca(2+)](i) plus NADH in the pipette) was attenuated by homocysteine. The homocysteine-mediated inhibition of the BK(Ca) amplitude was suppressed by Tiron (10 mM) or diphenylene iodonium (30 nM), applied alone, but not by superoxide dismutase (500 U/ml) and catalase (500 U/ml). Generation of superoxide (O(2)(-)) of the smooth muscle cells (with NADH presence), measured using the lucigenin-enhanced chemiluminescence, was markedly increased by angiotensin II (100 nM) and homocysteine (30 microM). The chemiluminescence signal was sensitive to apocynin (300 microM) or Tiron, applied alone, but not to superoxide dismutase and catalase. In conclusion, our results demonstrate that acute homocysteine application inhibits the iberiotoxin-sensitive BK(Ca) channels (with elevated [Ca(2+)](i) and NADH present) which is probably caused by the NADH oxidase activation and the concomitant generation of intracellular superoxide.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, PR China.
authors.forename: Alice L S
authors.initials: AL
authors.lastname: Au
authors.forename: S W
authors.initials: SW
authors.lastname: Seto
authors.forename: S W
authors.initials: SW
authors.lastname: Chan
authors.forename: M S
authors.initials: MS
authors.lastname: Chan
authors.forename: Y W
authors.initials: YW
authors.lastname: Kwan
mesh_terms: D014013:1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium Salt / Q000494:pharmacology; D000098:Acetophenones / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D003331:Coronary Vessels / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006710:Homocysteine / Q000031:analogs & derivatives / Q000494:pharmacology*; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology*; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D024681:Potassium Channels, Calcium-Activated / Q000187:drug effects* / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D013552:Swine; D014662:Vasoconstrictor Agents / Q000494:pharmacology
chemical_list: D000098:Acetophenones; D001562:Benzimidazoles; D004791:Enzyme Inhibitors; D010455:Peptides; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D014662:Vasoconstrictor Agents; D006710:Homocysteine; D009243:NAD; D013481:Superoxides; D000804:Angiotensin II; C086491:NS 1619; D014013:1,2-Dihydroxybenzene-3,5-Disulfonic Acid Disodium Salt; C064719:iberiotoxin; C056165:acetovanillone; C007957:homocysteine thiolactone; D019255:NADPH Oxidases; D002118:Calcium