Rapid formation of tight junctions in HT 29 human adenocarcinoma cells by hypertonic salt solutions

The human colon adenocarcinoma cell line HT 29 grows virtually without tight junctions (TJ) under standard culture conditions. Earlier studies have shown that focal TJ (fasciae occludentes) can be rapidly assembled in this cell line under the influence of various proteases. Here we show that focal TJ can be induced in this cell line by a brief treatment with appropriate salt solutions. Induction by ammonium sulfate in Hanks' buffer reached a maximum value after 15 to 30 min. The amount of TJ increased with the salt concentration and reached a plateau value at a concentration of 160 mM ammonium sulfate. The amount and complexity of TJ induced by ammonium sulfate were similar to those in experiments using trypsin as inducing agent as shown by morphometric analysis. At 0 degrees C, no TJ were formed under the influence of the salt. A comparative study of TJ induction using a variety of inorganic and organic salts gave the following results. All alkali sulfates induced TJ, although with different yield. Both calcium and magnesium chloride were potent inducers. Ammonium and sodium salts encompassing a variety of anions covered a wide range from maximum induction (sulfate, citrate) to almost complete absence of induction (nitrate). Sodium chloride did not induce any TJ. It follows that the induction of TJ is a specific effect of individual ionic components of the solution as opposed to a general effect of osmolarity and ionic strength. The data suggest tentatively that antichaotropic but not chaotropic ions have the potential to trigger the formation of TJ in this experimental system.