Synergistic induction of alkaline phosphatase in colonic carcinoma cells by sodium butyrate and hyperosmolality.

Exposing HT-29 cells to the combination of two inducers of intestinal alkaline phosphatase, sodium butyrate and hyperosmolality, causes a synergistic (over 1000-fold) increase in specific activity. Evidence is presented showing that enzyme induction is reversible; the half-life of the induced activity is approximately 30 h. Preinduction by butyrate or by hyperosmolality does not prime the cells so as to respond synergistically when subsequently exposed to hyperosmolality or butyrate, respectively. This study demonstrates that when applied in combination, the effect on gene expression by one alkaline phosphatase inducer is amplified by the other.