RELATION BETWEEN CHLORIDE SECRETION AND INTRACELLULAR CYCLIC ADENOSINE-MONOPHOSPHATE IN A CLONED HUMAN INTESTINAL-CELL LINE HT-29 CL 19A

The relation between the intracellular cyclic adenosine monophosphate (cAMP) content and the electrogenic chloride secretion induced by chol era toxin was studied in secretory HT-29 cl 19A cell monolayers. Cells were treated by the mucosal addition of cholera toxin (5 mu g/ml) for 10, 45, or 90 minutes in Ussing chambers. After 10 minutes, the mean (SEM) intracellular cAMP content (3.2 (0.2) pmol/mg protein) and short circuit current (Isc) (1.9 (0.3) mu A.cm(-2)) did not differ signific antly from the corresponding basal values. At 45 minutes, a significan t increase in the Isc (22.2 (5.7) mu A.cm(-2)) was accompanied by a si gnificant elevation in cAMP (10 (1.7) pmol/mgh protein). At 90 minutes , when the stimulated Isc plateaued (35.2 (5.2) mu A.cm(-2)), the cAMP value (99.2 (23.8) pmol/mg protein) increased further. The protein ki nase C (PKC) activity of the cells was not affected by cholera toxin. Treatment of cell monolayers by different concentrations of DbcAMP (10 (5), 5x10(-5), 10(-3) M) showed that the minimal concentration of DbcA MP (serosal) which significantly increased the Isc (Delta 4.5 mu A.cm( -2)) was 10(-4) M, and that this was accompanied by an increase in cAM P of Delta 6.7 pmol/mg protein; Compared with DbcAMP, cholera toxin st imulated the Isc (at 45 minutes) to a much higher degree with a compar able elevation of cAMP. It is concluded that in cl 19A cells there is a threshold value of increase in intracellular cAMP that induces chlor ide secretion. Cholera toxin stimulated chloride secretion can be expl ained predominantly by an increase in intracellular cAMP that is unrel ated to PKC activity.