Glucose transport across the gill of the rainbow trout, Salmo gairdneri.

Glucose fluxes across the gills were measured in freshwater-adapted trout (Salmo gairdneri) using an in vitro, perfused-head preparation. A large asymmetry was observed for the primary lamellar pathway, glucose permeability in the serosa-to-mucosa direction being up to 24 times greater than the permeability in the mucosa-to-serosa direction. Chloride cells appeared to possess a maximal rate of transport, or TMG, of 79 mumol/hr per 100 g. Phlorizin, phloretin and, to a lesser extent, harmaline caused an increase in the rate of glucose efflux. The results suggest that the tubulo-vesicular reticulum, into which plasma is introduced under low pressure, may be regarded as a reabsorption site for glucose in a way similar to the nephron proximal tubule. Thus, essential molecules such as glucose are removed while excess or non-essential substances are excreted into the external medium.