Control of ion transport by Gillichthys mirabilis urinary bladder.

The columnar epithelial cell region of the goby Gillichthys mirabilis urinary bladder is the region responsible for active Na and Cl reabsorption from bladder urine. In 5% seawater-adapted fish, reabsorption occurs via an electrically silent coupled NaCl transport mechanism. Bladder reabsorption is increased in seawater-adapted fish above that observed in 5% seawater-adapted fish; incremental reabsorption results from an electrogenic Na transport in addition to the neutral component. Hypophysectomy of seawater-adapted fish reduces the electrogenic Na transport (measured as short-circuit current, ISC) and increases the transepithelial resistance (R) to values near those of 5% seawater-adapted fish. Cortisol restores the ISC and R to normal seawater-adapted values and will initiate electrogenic Na transport in 5% seawater-adapted fish. Ovine prolactin will also restore the ISC and R of columnar cell regions of hypophysectomized seawater-adapted fish to normal seawater-adapted levels; this effect appears to be due to contamination or to inherent stimulatory activity of the ovine prolactin preparation, since endogenous prolactin is ineffective in the restoration of ISC or R.