Weak acid accumulation in the serosal extracellular compartment of the frog gastric mucosa

The dimethyloxazolidine dione distribution in the extracellular compartments of the frog gastric mucosa was analyzed by washout kinetics. The volumes of the two extracellular compartments, serosal and mucosal, were estimated by inulin washout as 0.435 +/- 0.019 and 0.176 +/- 0.018 microliter/microliter tissue water, respectively. In the serosal extracellular space, significant dimethyloxazolidine dione accumulations of 2.63 +/- 0.25, 2.28 +/- 0.16, and 1.86 +/- 0.08 times that of the bathing media were found for bathing solutions with pH values of 6.9, 7.4, and 7.9 respectively. A high pH of the serosal extracellular fluid by itself could not account for the high values of dimethyloxazolidine dione accumulation. A difference in the total dimethyloxazolidine dione accumulation requires: (a) the existence of differences in the pH values and also the existence of a difference in the diffusion coefficient of the two forms of dimethyloxazolidine dione; or (b), a binding of one of the two forms, i.e., binding of dimethyloxazolidine dione form by fixed charges.