Problem: Your large intestine absorbs sodium that passes through it; that is, sodium moves from the lumen of the large intestine across the epithelial cells lining it and then through interstitial fluid into the blood. Assuming the concentrations of sodium are as follows: Lumen of large intestine: 300mM, Epithelial cell: 5mM; Interstitial fluid: 150mM, where on the epithelial cells are we likely to find open sodium channels? a) on all surfaces of the epithelial cell b) on the apical side (facing the lumen of the large intestine) c) on the basolateral side (facing the interstitial fluid/blood vessel) d) nowhere in the epithelial cells