Effect of cholera toxin on cAMP levels and Na+ influx in isolated intestinal epithelial cells

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Abstract
Freshly isolated chicken intestinal cells contain approximately 20 pmol adenosine 3',5'-cyclic monophosphate (cAMP)/mg cellular protein. Incubation with 3 micrograms/ml cholera toxin (CT) at 37 degrees C induces an elevation of cellular cAMP beginning 10-15 min after initial exposure. The response is linear with time for 40-50 min and causes a six- to eightfold increase over control levels at steady state. Dibutyryl cAMP and agents that increase cAMP production inhibit Na+ influx into the isolated enterocytes. Chlorpromazine completely abolishes the toxin-induced elevation of cAMP in the isolated cells and also reverses the effect on Na+ entry. The data provide evidence for a cAMP-mediated control of intestinal cell Na+ uptake, which may represent the mechanistic basis for the antiabsorptive effect of CT on Na+ during induction of intestinal secretory activity. Studies on the time-dependent effects of chlorpromazine on both intracellular cAMP concentration and Na+ influx suggest that the reactivation of the Na+ transport system after cAMP-induced inhibition is slow relative to the disappearance of cAMP.