title: Na(+) and Cl(-) transport by the urinary bladder of the freshwater rainbow trout (Oncorhynchus mykiss).
abstract: 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 microA 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 approximately +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.
authors.affiliation: Department of Biology, McMaster University, Hamilton, Ontario, Canada.
authors.forename: D W
authors.initials: DW
authors.lastname: Burgess
authors.forename: M D
authors.initials: MD
authors.lastname: Miarczynski
authors.forename: M J
authors.initials: MJ
authors.lastname: O'Donnell
authors.forename: C M
authors.initials: CM
authors.lastname: Wood
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D002740:Chlorothiazide / Q000494:pharmacology; D004594:Electrophysiology; D066298:In Vitro Techniques; D017136:Ion Transport; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D012966:Sodium Cyanide / Q000494:pharmacology; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002712:Chlorides; D002034:Bumetanide; D002740:Chlorothiazide; D000584:Amiloride; D012964:Sodium; D012966:Sodium Cyanide; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid