Active sulfate secretion by the intestine of winter flounder is through exchange for luminal chloride

Abstract

SO[Formula: see text]transport by winter flounder intestine in Ussing chambers was characterized. With 50 mM SO[Formula: see text] (physiological level) bathing the lumen, net absorption (lumen to blood) dominated. Under short-circuited conditions, 1 mM SO[Formula: see text] on both sides, net active SO[Formula: see text] secretion occurred (8.55 ± 0.96 nmol · cm−2 · h−1). NaCN (10 mM), ouabain (10−4 M), and luminal DIDS (0.2 mM) inhibited net secretion. Removal of luminal Cl− and HCO[Formula: see text] together (Cl−-HCO[Formula: see text]) or Cl− alone blocked net secretion, whereas removal of luminal HCO[Formula: see text] alone increased net secretion. SO[Formula: see text] uptake into foregut brush-border membrane vesicles was stimulated by a trans-Cl− gradient (in > out) and unaffected by a trans-HCO[Formula: see text] gradient (in > out). Short-circuiting with K+ (in = out) and valinomycin had no effect on Cl−-stimulated SO[Formula: see text] uptake, suggesting electroneutral exchange. Satiety (i.e., full stomach) stimulated the unidirectional absorptive flux, eliminating net secretion. It was concluded that the intestine is a site of SO[Formula: see text] absorption in marine teleosts and that active SO[Formula: see text] secretion is in exchange for luminal Cl−.