PELIS, R.M. *; RENFRO, J.L.: Active Sulfate Secretion by the Intestinal Epithelium of Winter Flounder is through Anion Exchange for Chloride
Marine teleosts are hypoosmotic to their surrounding environment and must continuously drink seawater to avoid dehydration. It is widely accepted that net absorption of monovalent ions (sodium and chloride) occurs across teleost intestinal epithelial cells and is required for water absorption. However, the transport of divalent ions (sulfate, magnesium and calcium) has been less intensively studied. The purpose of the current study was to determine the direction and mechanism of sulfate transport by the intestinal epithelium of winter flounder (Pleuronectes americanus). Isolated intestinal epithelium was mounted in paired Ussing chambers for determination of electrical properties and unidirectional radiolabeled sulfate (35S) transport. Electrical potential difference (PD) across the epithelium averaged 0.83 � 0.17 mV (serosa negative) while the resistance averaged 37.1 � 3.81 ohm x cm2. Net transport of 35S was 7.42 � 1.01 nmoles/cm2/hr and in the direction of secretion (blood to lumen). Ouabain (0.1 mM) abolished the PD and reduced net secretion 70% by inhibiting the secretory flux only. Similarly, the anion exchange inhibitor DIDS (0.2 mM) reduced net secretion 55 % through inhibition of the secretory flux. Removal of chloride alone, and chloride and bicarbonate together from the apical bath solution significantly reduced net secretion of sulfate, while removal of bicarbonate alone had no effect. These preliminary data indicate that the intestinal epithelium of winter flounder actively secretes sulfate possibly by exchanging for chloride. Supported by NSF.
