Ion transport and structure of urinary bladder epithelium of Amphiuma

The urinary bladder of Amphiuma exhibits stable transport properties and an electrical potential difference in vitro. The lumen is significantly negative to the serosa and under short-circuited conditions flux rations for Na and Cl of 5.92 +/- 0.42 and 1.81 +/- 0.20, respectively, were observed. The close agreement between the short-circuit current and net Na flux suggests that most, if not all, of the current is carried by Na. Both ouabain and amiloride decreased the short-circuit current and the mucosal-to-serosal (M leads to S) flux of Na. Furosemide caused a transient increase in the M leads to S flux of Na and Cl but ADH was without effect. In bladders that had high transmural resistance, a net movement of K in the M leads to S direction under short-circuited conditions with flux ratios of up to 2 could be observed. The epithelium of the Amphiuma bladder consists of three cell types: granular cells, basal cells, and mitochondria-rich cells. No goblet cells are present. The mitochondria-rich cells comprise less than 5% of the population of the surface epithelium in Amphiuma in contrast to other amphibian bladders, where it accounts for up to 25% of the population.