The effect of theophylline on intestinal bicarbonate transport measured by pH stat in Amphiuma.

1. The influence of theophylline on the mucosa to serosa and serosa to mucosa fluxes of HCO3- were measured by the pH stat technique in isolated segments of proximal small intestine from Amphiuma maintained under short-circuited conditions. The mucosal or serosal fluid was exposed to media containing 25 mM-HCO3- (pH 7.4) while the pH of unbuffered media in the opposite compartment was maintained by addition of acid. 2. Theophylline significantly increased the secretory flux of HCO3- and significantly reduced the absorptive flux when measured in Cl- -free (SO4(2-)) media. 3. In normal media theophylline did not alter the secretory flux but significantly lowered the absorptive flux of HCO3-. 4. Acetazolamide (0.1 mM) inhibited the theophylline-stimulated secretory flux of HCO3- and reduced the effect of theophylline on the absorptive flux. 5. In normal intestine there was an inequality between the secretory or absorptive HCO3- flux and the short-circuit current (Isc) consistent with the presence of Cl- absorption. After addition of theophylline the Isc was more nearly equal to the net secretory or absorptive HCO3- flux. 6. Exogenous cyclic AMP had effects identical with theophylline. 7. The results provide strong evidence that elevation of cyclic AMP stimulates net HCO3- secretion in urodele small intestine and provide indirect evidence that Cl- absorption is simultaneously reduced.