Applied pressures and net water flux across in vitro frog gastric mucosa

The effects of hydrostatic pressure differences up to 0.4 atm/413 cmH2O were studied on frog gastric mucosa in vitro. Net water flux, transmucosal electrical potential difference, and acid secretion were measured. A significant correlation between hydrostatistic pressure difference and net water flow (r=0.77) was obtained. The intercept of the regression line, at zero hydrostatic pressure difference, is 9.3 +/- 0.5 microliter/cm2.h, and the slope 42.9 +/- 3.2 microliter/cm2.atm.h. No significant correlation was obtained between the hydrostatic pressure difference and the transmucosal potential difference (P greater than 0.20), the acid secretion (P greater than 0.20), or the nonacidic chloride transport, measured as short-circuit current (P greater than 0.20). Hydrostatic water flux is compared to osmotically induced flux previously reported. It is proposed that the difference between hydrostatic and osmotic induced water fluxes is due to the area of cells exposed to the pressures. Only part of surface cells are directly exposed to the osmotic pressure due to the presence of restricted extracellular compartments.