Failure of Thiocyanate to Influence The Flux of Sodium Through The Isolated Frog Gastric Mucosa

Isolated stomachs from mammals showed substantial active absorption of sodium (Am.]. Dig. Dis. 14:221-238, 1969) in contrast to isolated frog gastric mucosa. Could the difference have been due to a "micro-environment" in the latter preparation based on fine structure features that maintained high H-ion concentration at the site of active transport? To answer this, H-ion secretion was inhibited in frog gastric mucosa with 15 mM thiocyanate. Unidirectional fluxes of sodium were not materially affected. These results cast doubt on a possible depression of active sodium absorption by a high H-ion concentration in the "microenvironment" of the isolated amphibian mucosa. A description of the major ionic movements through the gastric mucosa which are associated with its electrophysiology and the production of HCl is beginning to emerge. Apart from the elasmobranchs (Hogben, 1967), the mucosae of vertebrates not only secrete acid but generate a characteristic transepithelial potential difference of about 35 mv, oriented such that the luminal face is negative with respect to the in~erstitial surface. Depending on the species and the preparation being studied, there appears to be two different origins for the generation of this electrical potential. In the case of the isolated frog gastric mucosa, for which most information is available, the situation is reasonably clear ( Hogben, 1965) . The transepithelial potential difference arises from a current of Clions that are being secreted towards the lumen or mucosa! surface at a rate in excess of the secretion in the same direction of H+ ions. A net movement of Na+, from mucosa to serosa, does not contribute significantly to the electrical current (Kitahara et al, 1969). There is a highly efficient transport of K+ from mucosa! to serosal surface but it is quantitatively insignificant (unpublished observations) . When the surface of the secreting gastric mucosa of the dog in situ is bathed by iso-osmotic H C 1, a more or less similar picture obtains (Rehm, 1953). Since neither Na+ or K+ are initially present at the mucosa! surface, there can not be a net ionic movement of either species from mucosa to serosa. Rather each moves or is secreted in the direction of interstitial fluid to lumen. Consequently, the electrical current must arise once again from a discrepancy between the rates at which Cland H+ are being secreted into the lumen, the former being favored. To our surprise the ionic movements encountered in the isolated mammalian stomach differ in an important respect. To a degree, 1 Department of Physiology and Biophysics. University of Iowa, Iowa City, Iowa.