Regarding the iodide pump in thyroid cells, which is NOT true?

• A. it is stimulated by TSH
• B. it depends on Na+ / K+ ATPase activity
• C. it pumps iodide into the colloid, after entering the cell down an electrical gradient
• D. it pumps iodide against an electrical gradient
• E. its activity can be measured with trace doses of radioactive iodine