title: Urea transport in toad skin (Bufo marinus)
abstract: Urea is transported from mucosa to serosa across the skin of the stenohaline toad, Bufo marinus, studied under short circuit current (SCC) conditions. Mucosal to serosal transepithelial urea transport (Jm-->s(urea)) was markedly and asymmetrically enhanced in toads adapted to hypertonic (150 mM) NaCl and showed saturation kinetics with an estimated Kd for urea in the bathing solution of approximately 1 mM and a maximal rate of Jm-->s(urea) = 9.4 nmol.cm-2 x hr-1, consistent with a carrier-mediated transport mechanism. Jm-->s(urea) in the skin of 150 mM NaCl-adapted toads was characterized with drugs known to affect transepithelial urea transport (J(urea)) in the urinary bladder of this species. Amiloride (10(-8)-10(-3) M) inhibited Jm-->s(urea) in a dose-dependent fashion, but with a potency only 1/1000th of that for inhibition of SCC in the same skins. Phloretin (< or = 5 x 10(-4) M) had no effect on Jm-->s(urea) or SCC; ouabain (5 x 10(-4) M) and NaCN (10(-3) M) had no effect on Jm-->s(urea) but inhibited SCC (indicating inhibition of active sodium transport) by 70 and 67%, respectively and vasopressin (10(-8) M) had no effect on Jm-->s(urea), but stimulated SCC 179% above base line. The pyrazinoyl amiloride analog, 2-pyrazinoylguanidine (10(-4) M), reported to inhibit urea transport in mammals, also had no effect on Jm-->s(urea), but inhibited SCC approximately 30%. A 1.5 unit pH gradient (m-->s or s-->m) had no effect on Jm-->s(urea).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pharmacology, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania.
authors.forename: G
authors.initials: G
authors.lastname: Dytko
authors.forename: P L
authors.initials: PL
authors.lastname: Smith
authors.forename: L B
authors.initials: LB
authors.lastname: Kinter
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002024:Bufo marinus / Q000502:physiology*; D006146:Guanidines / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology; D010693:Phloretin / Q000494:pharmacology; D011719:Pyrazines / Q000494:pharmacology; D012867:Skin / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology; D014508:Urea / Q000378:metabolism*; D001743:Urinary Bladder / Q000378:metabolism
chemical_list: D006146:Guanidines; D011719:Pyrazines; D001127:Arginine Vasopressin; D012965:Sodium Chloride; D010042:Ouabain; C056104:2-pyrazinoylguanidine; D000584:Amiloride; D014508:Urea; D010693:Phloretin