Effects of prolonged saline exposure on water, sodium and urea transport and on electron-microscopical characteristics of the isolated urinary bladder of the toad Bufo bufo.

1. A comparison was made of various transport properties and electron-microscopical characteristics of isolated urinary bladders from toads (Bufo bufo) maintained in either tap water or 0.7% saline (0.7 g NaCl in 100 ml. H(2)O) for 10 days to 2 months.2. In the absence of Pitressin, isolated bladders from saline-adapted toads showed:(a) markedly, and significantly, lower osmotic water flow;(b) moderately, but not significantly, lower urea permeability;(c) no significant change in net sodium transport (measured as short-circuit current, I(sc)); and(d) significantly smaller intercellular space/mucosal cell ratios in electron-micrographs.3. Differences in the transport and electron-microscopical characteristics between bladders from water-exposed and saline-adapted toads became more evident in the presence of exogenous Pitressin (10 m-u./ml. serosal solution):(a) the stimulating influence of Pitressin on osmotic water flow, short-circuit current and urea permeability was considerably smaller in bladders from saline-adapted toads than in those from water-exposed toads;(b) the influence of Pitressin on short-circuit current was reduced more profoundly than that on either water flow or urea permeability;(c) the Pitressin-induced increment in intercellular space/mucosal cell ratio was significantly smaller in electron-micrographs of bladders from saline-adapted toads than in those from water exposed toads.4. The effects of saline adaptation are discussed in relation to decreased permeability of mucosal membrane barriers.