Freshwater (FW) rainbow trout (Oncorhynchus mykiss) urinary bladders mounted in vitro under symmetrical saline conditions displayed electroneutral active absorption of Na+ and Cl- from the mucosal side; the transepithelial potential (V(t)) was 0.1 mV, and the short-circuit current was less than 1 μA cm-2. Removal of Na+ from mucosal saline decreased Cl- absorption by 56% and removal of Cl- decreased Na+ absorption by 69%. However, active net absorption of both Na+ and Cl- was not abolished when Cl- or Na+ was replaced with an impermeant ion (gluconate or choline, respectively). Under physiological conditions with artificial urine ([Na+] = 2.12 mM, [Cl-] = 3.51 mM) bathing the mucosal surface and saline bathing the serosal surface, transepithelial potential (V(t)) increased to a serosal positive ~+7.6 mV. Unidirectional influx rates of both Na+ and Cl- were 10-20-fold lower but active absorption of both ions still occurred according to the Ussing flux ratio criterion. Replacement of Na+ with choline, or Cl- with gluconate, in the mucosal artificial urine yielded no change in unidirectional influx of Cl- or Na+, respectively. However, kinetic analyses indicated a decrease in maximum Na+ transport rate (J(max)) of 66% with no change in affinity (K(m)) in the low Cl- mucosal solution relative to the control solution. Similarly, there was a 79% decrease in J(max) values for Cl-, again with no change in K(m), in the low-Na+ mucosal bathing. The mucosal addition of DIDS, amiloride or bumetanide (10-4 M) had no effect on either Na+ or Cl- transport, under either symmetrical saline or artificial urine/saline conditions. Addition of the three drugs simultaneously (10-4 M), or chlorothiazide (10-3 M), under symmetrical saline conditions also had no effect on Na+ or Cl- transport rates. Cyanide (10-3 M) addition to mucosal artificial urine caused a slowly developing decrease of Na+ influx to 59% and Cl- influx to 50% in the period after drug addition. Na+ and Cl- reabsorption appears to be a partially coupled process in the urinary bladder of O. mykiss; transport mechanisms are both dependent upon and independent of the other ion. (C) 2000 Wiley-Liss, Inc.
|Original language||English (US)|
|Number of pages||14|
|Journal||Journal of Experimental Zoology|
|State||Published - Jun 15 2000|
ASJC Scopus subject areas
- Animal Science and Zoology