Estimation of sodium uptake through the gill of the rainbow trout Salmo gairdneri.

Sodium exchanges through the gill epithelia were estimated in the rainbow trout, Salmo gairdneri, using the perfused head technique. The head tissues accumulate radioactivity. In addition there exists an extrabranchial entry of sodium, which is 20 times smaller than the branchial one. The study of the evolution of venous and arterial sodium specific activities as a function of time is necessary before flux measurements are achieved. Contrary to previous studies, an uptake at the primary lamella level is demonstrated. Uptake of sodium through the secondary lamellae can be measured rapidly while at least 30 min are needed for measurement of uptake through the primary lamellae. Chloride cells of the primary lamellae contribute to about 20% of the total sodium uptake.