Ammonia absorption in hamster ileum: effect of pH and total CO2 on transport in everted sacs

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Abstract
The movement of ammonia nitrogen (NH3N) was tested in isolated sacs of everted hamster ileum at varying concentrations of H ion and total CO2. When pH differentials between the mucosal and serosal compartments were maintained by the repeated addition of acid or base to the mucosal solutions, ammonia absorption remained quantitatively constant regardless of the final pH gradients. As the concentration of total CO2 in the original test solution was reduced, ammonia transport decreased. In the absence of CO2 the NH3N concentration of fluid crossing the ileal wall was no greater than that of the initial test solution, whereas, at 20 mM of total CO2 the solution transport contained a 2-fold increment in NH3N concentration Acetazolamide, 5 x 10-3 M, in the test solution caused no inhibition of ammonia absorption. The data support a CO2-HCO3- dependent transport mechanism that is not inhibited by acetazolamide and does not conform to principles of nonionic diffusion.