Kinetics of acetylsalicylate and D-lactate transport across isolated frog gastric mucosa.

Luminal to submucosal migration of 14C-acetylsalicylate and D-lactate and some electrical properties were studied in isolated frog gastric mucosae. With both compounds, the unionized acids permeated much more rapidly than the ionized conjugate bases. The permeability coefficient for unionized acetylsalicylic acid increased from 0.27 to 0.43 mumoles, h-1, cm-2, mM-1 when its luminal concentration was increased above 3 mM. Simultaneously there was an increase in mucosal ion conductance. Acetylsalicylic acid has been shown previously to increase gastric mucosal permeation of ions and uncharged larger molecules. The present results indicate that above a threshold concentration the unionized form also enhances absorption of this drug per se. Unionized D-lactic acid had no effect of mucosal ion conductance and the permeability coefficient (0.07 mumoles, h-1, cm-2, mM-1) was independent of its luminal concentration.