Dextran Permeability, Electrical Properties, and H+ Secretion in Isolated Frog Gastric Mucosa After Acetylsalicylic Acid

Exposure of the secretory (luminal) side of the isolated frog gastric mucosa to 5 or 10 mm acetylsalicylic acid (ASA), mainly in the unionized form at pH 3.00, results in marked permeability changes. The mucosa normally impermeable to the trisaccharide raffinose allows much larger dextran molecules to pass through after exposure to ASA. Dextran permeability is probably characterized by molecular sieving with a molecular weight of about 30,000 as the upper limit for permeation. This corresponds to an equivalent diffusion radius of about 40 Å. These concentrations of un-ionized ASA also depress H+ secretion and reduce the resistance, electrical potential difference, and short circuit current. While a lower concentration of un-ionized ASA at pH 3.00 (1 mm) or 10 mm ionized ASA (pH 7.12) depressed the H+ secretion rate they affect neither the saccharide permeability nor the electric properties. Thus increased permeability to the nonelectrolytes is associated with increased ionic conductivity (decreased resistance). Depression of the electrogenic properties reflects probably some degree of internal short-circuiting in the abnormally permeable mucosa and also a direct inhibition of the electrogenic transport properties.