Sodium uptake by isolated-perfused gills of rainbow trout ( Salmo gairdneri)

1. 1. Individual gill arches of rainbow trout ( Salmo gairdneri) were surgically prepared and perfused ( in vitro) with various solutions, using a constant pressure perfusion apparatus. 2. 2. When gills were perfused with Ringer solution with a normal or slightly elevated sodium concentration, there was a small but significant loss of sodium into the bathing medium. Perfusion with Ringer solution in which the sodium concentration was less than normal, always resulted in a net uptake of sodium. 3. 3. The sodium concentration of the perfusion fluid, and epinephrine, appear to control the rate of sodium uptake by the gill. 4. 4. The effects of ouabain, cyanide and iodoacetate indicate that sodium uptake is ATP-dependent and that the ATP is produced via aerobic metabolism. 5. 5. The rate of sodium uptake was found to be generally independent of the rate and pattern of fluid through the gill.