Ion transport by the urinary bladder of the gobiid teleost, Gillichthys mirabilis

Transport characteristics of the two epithelial cell types lining the urinary bladder of the goby can be studied in Ussing-type chambers. Cuboidal cell regions from seawater- and 5% seawater-acclimated fish exhibit little mucosa-to-serosal Na or Cl transport. In contrast, columnar cell regions from both seawater- and 5% seawater-acclimated fish transport substantial amounts of Na and Cl. Whereas all electrolyte transport in 5% seawater-acclimated fish is electrically silent (neutral), columnar cell regions from seawater-acclimated fish possess an electrogenic Na transport component in addition to the neutral transport. Columnar cell regions also possess a Cl/Cl exchange diffusion mechanism. Neutral Na and Cl transport are not altered in response to external salinity; electrogenic transport varies both with acclimation to salinity and season. Reabsorption of Na and Cl from urine reduces excretory losses of these ions from 5% seawater-acclimated fish and drives urinary bladder water reabsorption in seawater-acclimated fish.