Ussing Chamber Measurement of Transepithelial Resistance

Inserts were mounted in modified Ussing chambers (P2300; Physiologic Instruments, San Diego, CA) and continuously short circuited with an automatic voltage clamp (VCC MC8; Physiologic Instruments) as described previously (Edinger et al., 2012 (link), 2014 (link)). The apical and basolateral chambers each contained 4 ml of Ringer solution (120 mM NaCl, 25 mM NaHCO₃, 3.3 mM KH₂PO₄, 0.8 mM K₂HPO₄, 1.2 mM MgCl₂, 1.2 mM CaCl₂, and 10 mM glucose). Chambers were constantly gassed with a mixture of 95% O₂, 5% CO₂ at 37°C, which maintained the pH at 7.4 and established a circulating perfusion bath within the Ussing chamber. Simultaneous transepithelial resistance was recorded by applying a 2-mV pulse per minute via an automated pulse generator. Recordings were digitized and analyzed using PowerLab (AD Instruments, Colorado Springs, CO).