Experiments were performed by exchanging half of the SFM-1 in Transwell or Snapwell chambers with ×2 concentrations of barium chloride (BaCl2) or calcium chloride (CaCl2) and inhibitors or ionophores that were diluted in SFM-1. Except caloxin 1b1, inhibitors were first dissolved in dimethyl sulfoxide (DMSO; AmericanBio, Natick, MA, USA) to create a stock solution and then diluted to the indicated concentrations on the day of the experiment (DMSO <1% of total media). Caloxin 1b1 (Anaspec, Inc., Fremont, CA, USA) was dissolved in SFM-1. Final concentrations were: 3.0 mM BaCl2 (Thermo Fisher Scientific, Rockford, IL, USA), 6.3 mM CaCl2 (Sigma-Aldrich Corp., St. Louis, MO, USA), 2.0 mM LaCl3 (Sigma-Aldrich Corp.), 5.0 μM valinomycin (R&D Systems, Minneapolis, MN, USA), 10 μM nifedipine (Alfa Aesar, Ward Hill, MA, USA), 20 μM ML204 (Sigma-Aldrich Corp.), 1.0 μM HC-067047 (Sigma-Aldrich Corp.), 100 μM ALLM (Santa Cruz Biotechnology, Dallas, TX, USA), and 400 μM caloxin 1b1. Solutions were added to apical and basolateral media chambers unless otherwise specified. After media exchange, tissue culture plates were agitated gently to mix the media and incubated at 37°C. The TER was measured before media exchange, and at 2 and 4 hours of incubation.