Lithium Secretion by the Salt Gland of the Goose

Abstract

THE mechanism by which the salt gland of marine birds secretes a hypertonic solution of sodium chloride is of considerable interest. It is generally considered that the concentration gradient for sodium is established across the luminal membrane of the secretory cell by an electrogenic sodium pump¹, but Hokin², on the basis of measurements of the intracellular composition of salt gland slices in vitro, argued that the concentration gradient is established across the basal membrane. One of us (M. P.)³ repeated these experiments, however, and was unable to confirm Hokin's figures for the sodium and chloride content of salt gland cells. M. P. again proposed that sodium is actively transported from the intracellular fluid of low sodium concentration to the lumen of the tubules. Nevertheless, this does not preclude the possibility suggested by Hokin² that sodium and chloride pass into the cell across the basal membrane by an active mechanism involving exchanges for H⁺ and HCO₃⁻; indeed, current evidence favours this view¹.