Gel filtration of the supernatant.

Supernatant is collected from 3-day-old nontransfected HT-29 cells (A), 3-day-old HT-29 cells transfected with a nonrecombinant plasmid (B), and 3-day-old HT-29 cells transfected with a plasmid-containing TC cDNA expressed in Caco-2 cells (C). The samples were injected on a Sephacryl S300 HR column and eluted with a 20 mM Tris HCl, pH 7.4; 0.7 M NaCl; 0.01% Triton; and 0.01% NaN₃ buffer. Cells transfected with the recombinant plasmid secrete additional TC.