Inhibition of Ca2+-induced relaxation by oxidized tungsten wires and paratungstate

Recent studies of rat mesenteric arteries using a wire myograph detected de creased Ca2+ and acetylcholine-induced relaxation responses. Preliminary ex periments indicated the reduced responses were associated with the tungsten wire used in the myograph system. Compared with earlier observations, arte ries mounted on aged 28-mum tungsten wire showed decreased maximal Ca2+-ind uced relaxation responses of arteries precontracted with phenylephrine (91. 9 +/-1.5 versus 54.8 +/-4.5%, p<0.001) and reduced sensitivity to Ca2+ (ED5 0 = 1.65<plus/minus>0.07 versus 4.58 +/-0.16 mM, p<0.001). Similar shifts w ere seen for acetylcholine. When the surface of the wire was cleaned by abr asion with fine sandpaper, both the ED50 for Ca2+ and maximal relaxation si gnificantly improved. An enhanced sensitivity to Ca2+ was also seen when ar teries were mounted on newly purchased 14-<mu>m tungsten or 14-mum 24K gold wire with the rank order: 14-mum gold > 14-mum tungsten >> 28-mum aged tun gsten wire. Laser Raman spectral analysis of the aged 28-mum tungsten wire showed that the surface was in an oxidized state that shared spectral chara cteristics with the paratungstate [W12O42](-12) anion. The effect of the pa ratungstate anion on arterial relaxation was therefore tested. Paratungstat e, but not the structurally dissimilar tungstate and metatungstate anions, significantly reduced the sensitivity and magnitude of relaxation induced b y Ca2+ and to a lesser extent, relaxation induced by acetylcholine. To lear n whether paratungstate inhibits relaxation through the generation of oxyge n radicals, the effect of the superoxide dismutase mimetic 4-hydroxy-2,2,6, 6-tetramethylpiperidine 1-oxyl (1 mM) was assessed and found to have no eff ect. Since Ca2+-induced relaxation is inhibited by iberiotoxin, the effect of paratungstate on K+ channel activity was assessed. Paratungstate had no effect on currents through large conductance, Ca2+-activated K+ channels in whole-cell recordings from vascular smooth muscle cells, ruling out an act ion at the BKCa channel. We conclude that: 1) surface oxidation of tungsten wire commonly used in wire myography significantly and adversely affects v ascular responses to vasodilator compounds, 2) the effect is likely mediate d by the paratungstate anion, and 3) the effects of the anion are not assoc iated with free radical generation or K+ channel inhibition.