Hormonal Control of Gill Na+,K+-ATPase and Chloride Cell Function

Abstract

This chapter examines the hormonal control of gill Na+, K+-ATPase and chloride cell function. The secretion of excess sodium and chloride by teleosts in seawater is carried out by gill chloride cells. These highly specialized cells are characterized by a large, columnar appearance, numerous mitochondria, an extensive tubular system, an apical crypt, and mucosal–serosal exposure. The breakdown of ATP is detected in the presence and absence of ouabain. Herndon found that prolactin treatment of seawater-adapted tilapia resulted in a dramatic reduction in chloride cell size without changing chloride cell density. Chloride cell height and the proportion of cells spanning the opercular membrane were reduced, suggesting that these cells were effectively removed as chloride secretory cells. Based on reductions in opercular membrane conductance and short-circuit current following prolactin the treatment of seawater-adapted tilapia, Foskett postulated that prolactin reduces chloride cell numbers and active transport in the remaining chloride cells. Working with the closely related but stenohaline Nile tilapia (Oreochromis niloticus), Pisam found that prolactin injection caused the appearance of the smaller β-chloride cells that were previously absent from these fish in seawater. © 1995, Academic Press, Inc.