TRANSPORT MECHANISMS THAT MEDIATE THE SECRETION OF CHLORIDE BY THE RECTAL GLAND OF SQUALUS-ACANTHIAS

The rectal gland of Squalus acanthias secretes chloride by a mechanism that has been termed ''secondary active transport'' because it depend s on the activity of Na-K-ATPase. As currently described, chloride ent ers the cell across the basolateral cell membrane via the 2 chloride: sodium: potassium cotransporter. The energy for this electroneutral up hill movement of chloride and potassium is provided by the gradient fo r sodium directed into the cell. Present in the basolateral cell membr ane is Na-K-ATPase that maintains the gradient for sodium. A potassium conductance, present as well in the basolateral cell membrane, recirc ulates the potassium. Chloride exits the cell across the luminal membr ane via CFTR, the chloride conductance. This mechanism is widely distr ibuted throughout vertebrates. This report reviews the experimental ob servations that led to the current definition of the mechanism of chlo ride transport in the rectal gland. (C) 1997 Wiley-Liss, Inc.