Modulation by homocysteine of the iberiotoxin-sensitive, Ca2+-activated K+ channels of porcine coronary artery smooth muscle cells

We evaluated the acute effect of homocysteine on the iberiotoxin-sensitive, Ca2+-activated K+ (BKCa) channels of the porcine coronary artery smooth muscle cells. NS 1619 (1 to 30 mu M) caused a concentration-dependent enhancement of the BKCa amplitude (recorded using the wholecell, membrane-rupture configuration) only with an elevated [Ca2+](i) of similar to 444 nM, but not with [Ca2+](i) of similar to 100 nM. Homocysteine (30 mu M) caused a small inhibition (similar to 16%) of the BKCa amplitude ([Ca2+](i) = similar to 444 nM), and a greater inhibition (similar to 77%) was observed with 100 mu M NADH present in the pipette solution. The inhibition persisted after washing. With NADPH (100 mu M), a smaller magnitude of inhibition (similar to 34%) of the BKCa amplitude was recorded. The NS 1619-mediated enhancement of the BKCa amplitude (with elevated [Ca2+](i) plus NADH in the pipette) was attenuated by homocysteine. The homocysteine-mediated inhibition of the BKCa 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 11 (100 nM)and homocysteine (30 mu M). The chemiluminescence signal was sensitive to apocynin (300 mu M) or Tiron, applied alone, but not to superoxide dismutase and catalase. In conclusion, our results demonstrate, that acute homocysteine application inhibits the iberiotoxin-sensitive BKCa channels (with elevated [Ca2+](i) and NADH present) which is probably caused by the NADH oxidase activation and the concomitant generation of intracellular superoxide. (c) 2006 Elsevier B.V. All rights reserved.