Small intestine and kidney proximal tubules absorb various inorganic and
organic solutes from the lumen and deliver them to the blood. For most
solutes, this absorption occurs against their concentration gradients and
is sodium-dependent. With respect to anions, absorptive as well as secre￾tory movements have been observed. Solute transport in proximal tubules
and small intestine occurs through a single-layer epithelium. The luminal
surface of the epithelial cell is enlarged by microvilli which form the
brush border. The antiluminal membrane contains no microvilli. Trans￾cellular transport involves translocation across the brush border and the
basolateral membrane and intracellular transport. In this review, we would
like to restrict ourselves to the discussion of the properties of anion trans￾port through the brush border and basolateral membranes and compare
the anion transport mechanisms in proximal tubules and small intestine.
We shall see that some anion transport mechanisms show similar proper￾ties in proximal tubules and small intestine, whereas others exhibit char￾acteristic differences with respect to substrate specificity, pH dependence,
and stoichiometry of cotransport with other ions. For a more complete
discussion of transepithelial anion transport in small intestine and renal
proximal tubule we refer to recent reviews on related topics (e.g., Binder
t 98 t ; Boulpaep 1979; Field 1981 ; Frdrn ter et al. 1973; Holmb erg et al.
1981; Jackson 1981; Malnic and Giebisch 1979; Schafer and Andreoli
1979; Schultz 1979, 1981 a,b; Ullrich 1973, 1976, 1979; Windhager 1979).