Sodium transport (cont"d: primarily in the lower gut. Typified by secondary active transport using a na/cl symporter (1:1 ratio); the transporter is activated by a na concentration gradient across the apical/luminal membrane. Binding of the na (already has high affinity) increases the affinity for the cl site for its substrate (i. e. chloride); when both ions bind, the protein undergoes some conformational change occurs to move the ions to the cytosolic side. Increase in content of prostaglandin e2 associated with cholera toxin. Cholera toxin does 2 things: (1) inhibits apical na/cl symporter, so can"t absorb nacl, and (2) punches holes in apical membrane, causing cl to leak out into the intestinal lumen (and water to follow). Pge2 is specific to the na/cl symporter, so giving electrolyte-rich juice (ginger-ale) can help overcome the net efflux of water. Solvent drag: solvent moves and drags all other substances dissolved in it along for the ride.