Die abhängigkeit der jodakkumulation in schilddrüsenschnitten von der ionalen zusammensetzung des inkubationsmediums und ihre beeinflussung durch herzglykoside

The influence of the external Na⁺ and K⁺ concentration and of ouabain on I⁻ uptake and release was studied in cow-thyroid slices blocked with propylthiouracil. It could be shown that the I⁻ transport is dependent on the presence of both Na⁺ and K⁺ ions. However, the dependence on Na⁺ seems to be more direct: the effect of removal of K⁺ and of the application of ouabain set in only after a latency period while the effect of Na⁺ removal was immediate. The half-time of I⁻ release due to removal of Na⁺ from the medium was markedly shorter than that due to K⁺ removal or that of the release caused by ouabain. However, the half-times in the latter two cases were similar. A thyroid slice kept for a long time under ouabain poisoning in a solution wherein 90% of the Na⁺ was replaced by Li⁺ was still able to accumulate I⁻ for a short time when brought back into a medium of normal Na⁺ content in spite of the uninterrupted presence of ouabain. The possible connections between the K⁺-Na⁺ transport mechanism and the I⁻ transport are discussed.

In principle two basically different relations can be thought of. Either the I⁻ transport is directly coupled with the Na⁺K⁺ exchange mechanism or the cation-concentration differences created by the Na⁺K⁺ transport system are a prerequisite for the I⁻ transport. The present results are taken to favour the latter assumption.