TISSUE AND CONCENTRATION-DEPENDENT EFFECTS OF SODIUM SELENITE ON MUSCLE-CONTRACTION

In this study, we demonstrated that sodium selenite with high doses (g reater than or equal to 10(-3) M) were potent in inducing a contractur e type effect on heart and smooth muscles. Selenite (Se), at a concent ration of 10(-3) M, caused a contracture effect in heart preparations. Also, low Se concentrations did not have any significant effect. Alth ough low concentrations of Se (greater than or equal to 10(-5) M) had a biphasic effects on acetylcholine (ACh) induced and spontaneous ileu m contractions, 10(-3) M selenite enhanced once more a contracture eff ect similar to that of the heart preparations. Replacing Ca2+ concentr ation of the bathing solution by twofold Ca2+ or Ca2+-free did not cha nge the effects of selenite (10(-5) M) on contractility of ileum prepa rations. In vascular smooth muscle, low concentration of selenite (<10 (-4)) had no significant effects on KCl, and phenylephrine-induced con tractions and acethylcholine-induced endothelium-dependent relaxations of isolated rabbit aorta. However, the contractions induced by phenyl ephrine and the relaxations induced by acetylcholine in rabbit aorta w ere depressed significantly by high concentration of selenite (10(-3) M). The results obtained by selenite exposure from these three differe nt types of tissue preparations first suggest that the high concentrat ion of selenite exposure induces some alterations in the functions of muscles and endothelium in a tissue- and dose-dependent manner. Second , this observed irreversible type of dysfunction of tissues induced by 10(-3) M selenite is not directly dependent on the Ca2+ entrance into the cytosol, but might be induced by the increase of intracellular Ca 2+ with the disturbance of Ca2+ regulation.