Distinct tetraionic permeability profiles in the three epithelial cells. (A) Concurrent fluxes of Na+, Cl−, Ca2+, and Mg2+ in MDCK I, MDKC II, and T84 monolayers (n = 3). (B) Comparison of tetraionic permeabilities at 37°C and 4°C for MDCK I, MDKC II, and T84 monolayers (n = 3).