Effect of Replacement of Medium Potassium by Sodium,Cesium or Rubidium on in Vitro Iodide Transport and Iodoamino Acid Synthesis by Rat Thyroid 1

Summary

Rat thyroid lobes were incubated in Krebs-Ringer-phosphate (KRP) solution containing ¹³¹I–. Their ability to concentrate and to organically bind ¹³¹I was compared with thyroid lobes incubated in KRP in which the potassium was replaced by equimolar amounts of sodium, rubidium, or cesium. Both uptake and organic binding of ¹³¹I were depressed by sodium substitution. ¹³¹I uptake was near normal but organic binding of ¹³¹I was markedly depressed with cesium substitution. Rubidium was as effective as potassium in maintaining both these functions. It is concluded that the cation concentration of the medium is important in the maintenance of both iodide transport and organic binding of that iodide which enters the thyroid gland. These two functions differ in their cation requirements since cesium restores the capacity to concentrate iodide to a much greater degree than it does the capacity for organic binding of iodine.