Abstract
1. 1. The iodide-concentrating mechanisms of normal sheep thyroid, mouse submaxillary, rat-mammary and rat-thyroid tumor tissue slices have been compared. 2. 2. The tissue/medium ratio of 131Iis greater for thyroid tissue than for the other tissues under identical conditions. 3. 3. The time to attain equilibrium is 80–120 min in thyroid tissues and 30–40 min in the other three tissues. 4. 4. The tissue/medium ratio of 131I of all four tissues is reduced to half the control value at 1–3 · 10 −5 M iodide and the association constants vary from 2.7–3.3 · 10 4 M. The differences in tissue/medium ratio of 131I appear to be a function of the capacity of the system rather than the affinity for iodide ion. 5. 5. Iodide accumulation in all four tissues can be shown to be a function of the external K + concentration with half maximal stimulation of the tissue/medium ratio of 131I attained at from 0.9–2.9 · 10 −3 M of added K +. 6. 6. The cardiac glycosides, ouabain and scilliroside, depress the tissue/medium ratio of 131I in all four tissues. Scilliroside is a more potent inhibitor than ouabain by an order of magnitude. This depression can be partially reversed by the addition of 30 mequiv./l of K +, Rb + or Cs + ions.
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