The effect of hydroxylamine on KATP channels in vascular smooth muscle and underlying mechanisms.
Hydroxylamine (HA) is a putative intermediate in the conversion of l-arginine to nitric oxide (NO). HA was reported to cause the relaxation of precontracted aorta strips; however, the ionic mechanisms of HA-induced vasorelaxation were not yet known. In the present study, the whole-cell patch-clamp technique was used to examine the effects of HA on ATP-sensitive K+ (K(ATP)) currents and membrane potentials in vascular smooth muscle cells from rat mesenteric arteries and underlying mechanisms. It was found that bath-applied HA reversibly enhanced K(ATP) currents in a concentration-dependent fashion with an EC50 of 54 +/- 3.4 microM and hyperpolarized the cell membrane from -48 +/- 5.2 to -65 +/- 7.5 mV (n = 6, p < 0.01). The increase in K(ATP) currents induced by HA was suppressed by superoxide dismutase (-380 +/- 45 to -160 +/- 20 pA, n = 4, p < 0.01) and N-acetyl-L-cysteine (-385 +/- 55 to -150 +/- 16 pA, n = 5, p < 0.01), indicating the involvement of different free radicals, including superoxide anion. Hypoxanthine/xanthine oxidase increased not only basal K(ATP) currents, but also HA-enhanced K(ATP) currents (from -355 +/- 40 to -480 +/- 62 pA, n = 6, p < 0.05). Sodium nitroprusside, a spontaneous NO donor, and a membrane-permeable cGMP analog (8-bromo-cGMP) were without effects on HA-enhanced K(ATP) currents or basal K(ATP) currents. Our results indicate that HA augmented K(ATP) channel activity and hyperpolarized cell membrane, possibly via increased free radical generation.
Tang
Guanghua
G
Department of Physiology, College of Medicine, University of Saskatchewan, Saskatoon, Canada.
Wu
Lingyun
L
Wang
Rui
R
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D019811:Hydroxylamine / Q000494:pharmacology*; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D008565:Membrane Proteins; D015221:Potassium Channels; C117780:mitochondrial K(ATP) channel; D019811:Hydroxylamine; D000255:Adenosine Triphosphate