FIG. 6.

Stimulation of cyclic AMP accumulation in T-84 cells by LTp. T-84 cells were grown to near confluence in petri dishes. The culture medium was changed to DMEM containing 1% FBS prior to the addition of LTps. After incubation with these LTps, the cells were assayed for intracellular cyclic AMP as described in the text. (A) Dose-response reaction of the cells to LTp. The final concentration of holotoxin of LTp in each medium is indicated. The incubation was continued for 8 h. (B) Time course of cyclic AMP accumulation due to LTp. The LTps were added [1.2 nM for native LTp, 0.2 nM for trypsin-treated native LTp, 180 nM for LTp(C199S), and 700 nM for LTp(187S)] to each dish. The incubation was continued for the period indicated. Symbols: •, native LTp; ○, trypsin-treated native LTp; ▪, LTp(C199S); ▴, LTp(C187S).