Galactose fluxes across brush border of hamster jejunal epithelium: effects of mucosal anaerobiosis.

We have determined unidirectional influxes by measuring rate of uptake between 0.5 and 1.0 min of incubation in 5 mm galactose.H-inulin was used to correct for galactose in residual mucosal solution. Influx was greatly depressed by removing Na from or adding 10 m phlorizin to the incubation medium. Influx was also greatly depressed by making the mucosal solution anaerobic during a 10-min preincubation period. The same severe inhibition of galactose influx by mucosal anaerobiosis also occurrend under conditions in which the epithelial cells did not gain Na. After taking into account the effect of the mucosal unstirred water layer, influxes could be normalized to a concentration of 1.0 mm at the membrane surface. It was estimated that at 1.0 mm the phlorizin-sensitive component of galactose influx was reduced 93% by 10 min of mucosal anaerobiosis. Unidirectional effluxes were estimated by subtracting steady-state downhill mucosal-to-serosal flux from influx. The ease of efflux was apparently augmented 2.8-fold by mucosal anaerobiosis. After 10 min of mucosal anaerobiosis, there was no longer any directional preference for movement of galactose across the brush border and there was no uphill transport, in spite of the persistence of a large Na gradient. These results provide strong evidence against the theory that ion gradients provide the major source of energy for directional preference and uphill transport. [ABSTRACT FROM AUTHOR]