Movement of thallium(I)-ions across the epithelium of intestinal segments in vitro of rats

Summary

• 1. The movement of Tl⁺-ions was investigated on both isolated non blood-perfused jejunal and ileal segments as well as on stripped colon segments in vitro of rats.

• 2. After having administered radioactively labeled ²⁰⁴Tl-(Tl₂SO₄) on either the mucosal or the serosal side of these preparations only, a preferential direction of the movement of Tl⁺-ions from the serosal to the mucosal side was observed.

  In jejunal segments, the ²⁰⁴Tl-radioactivity at the mucosal side reached a concentration equilibrium with the concentration administered at the serosal side of the preparations. In colon segments a concentration gradient of more than 2 was established between the mucosal and the serosal side. In ileal segments the concentration of ²⁰⁴Tl-radioactivity in the mucosal fluid reached roughly 80% of that administered at the serosal side.

• 3. The amount taken up into the intestinal tissue is much higher after having administered the ²⁰⁴Tl-radioactivity from the serosal side than from the mucosal side. This holds true for jejunal ileal, and colonic segments.

• 4. In equilibrium experiments of non-everted colonic segments which were incubated on either side with the same ²⁰⁴Tl-concentrations the net transfer of ²⁰⁴Tl was determined directly. After a delay of 60 min the net transfer of ²⁰⁴Tl follows the rapid uptake into the intestinal tissue.

• 5. The net transfer as well as the tissue content of ²⁰⁴Tl decreases with increasing concentrations. From concentrations of ²⁰⁴Tl-ions of 5×10^-5M on, no concentration gradient between the mucosal and the serosal side could be established.

• 6. The net transfer of ²⁰⁴Tl depends highly on temperature. At 29°C a diminished concentration gradient of the ²⁰⁴Tl between the mucosal and the serosal fluid was observed. At 25°C no concentration gradient could be established. The content of ²⁰⁴Tl in tissue, however, was not affected by this decrease of temperature.

• 7. The net transfer of ²⁰⁴Tl is nearly doubled by an increase of the K⁺-concentration at the mucosal side from 4.5 (normal) up to 72 mM, whereas the change of the ²⁰⁴Tl-content in tissue was statistically not significant.

A decrease, however, of the net transfer of ²⁰⁴Tl is the consequence of an increased K⁺-concentration at the serosal side. In these segments the ²⁰⁴Tl content in tissue is decreased by 16% at the highest concentration of K⁺-ions.