Inhibition of iodide accumulation by perchlorate and thiocyanate in a model of the thyroid iodide transport system

Abstract

Abstract. The manner of inhibition of thyroid I− accumulation by perchlorate (ClO4−) and thiocyanate (SCN−) was studied using a newly developed biological model of the I− transport system. ClO4− inhibited I− accumulation in phospholipid vesicles made from thyroid plasma membrane and soybean phospholipids by decreasing Na+-dependent I− influx. The anion did not at all induce I− leakage from the vesicles. On the basis of Lineweaver-Burk plot analysis, it did not change Vmax for I− concentration. These results suggest that ClO4− is a competitive inhibitor of thyroid I− transport. In contrast, SCN− did increase I− leakage from the phospholipid vesicles to diminish I− accumulation. This anion might cause only slight depression of Na+-dependent I− entry, if any. The results do not support the idea that SCN− may be a competitive inhibitor, in spite of the fact that the anion did not change Vmax for I− transport on the basis of Lineweaver-Burk plot analysis.