PELIS, R.M.*; RENFRO, J.L.; Univ. of Connecticut, Storrs; Univ. of Connecticut, Storrs: Active Sulfate Secretion by the Intestine of Winter Flounder, Pleuronectes americanus
Marine teleosts are hypoosmotic to their surrounding environment and must continuously drink seawater to avoid dehydration. It is widely accepted that water uptake across the marine teleost intestine is driven by active absorption of monovalent ions (Na and Cl). However, intestinal transport of divalent ions (SO4, Mg, and Ca) has been less intensively studied. In this study, SO4 transport by winter flounder (Pleuronectes americanus) intestine was characterized in Ussing chambers. Under short-circuited conditions and 1 mM SO4 on both sides, net active SO4 secretion (blood-to-lumen) occurred (7.42 � 0.63 nmoles/cm/hr). During satiety (i.e., full stomach) net transport was reduced to zero. Treatment with NaCN (10 mM) or ouabain (0.1 mM) inhibited net secretion indicating dependence on metabolism and the plasma membrane Na gradient. Luminal treatment with the anion exchange inhibitor 4,4′-diisothiocyanatostilbene-2-2′-disulfonic acid (DIDS, 0.2 mM) also inhibited net secretion. Removal of Cl alone, and Cl and HCO3 together from the luminal bath solution reduced net SO4 secretion. Removal of HCO3 alone stimulated net secretion. Sulfate uptake into foregut brush-border membrane vesicles was stimulated by a trans-Cl gradient (in>out), and unaffected by a trans-HCO3 gradient (in>out). Short-circuiting with K, in=out, and valinomycin had no effect on Cl-stimulated SO4 uptake suggesting electroneutral exchange. These data indicate that the winter flounder intestine actively secretes SO4 by exchanging for luminal Cl. This process may function in water absorption and in the maintenance of plasma SO4 homeostasis. Supported by NSF.
