Figure 2.

TJ blockade by the selective deposition of BaSO₄. This maneuver permits us to certify that the early drop of TER that takes place in response to basolateral Ca²⁺ withdrawal results from the opening of TJs. The urinary bladders were initially short-circuited and bathed on the apical side by 75 mM KCl and on the basolateral side by Na₂SO₄ Ringer's (clear bars) or NaCl Ringer's (hatched bars). (A) TER was evaluated 120 s after the beginning of TER drop in response to basolateral Ca²⁺ removal. (B) The apical solution was then replaced by 50 mM BaCl₂ and TER was evaluated after 20 s. (C) Without removing Ba²⁺, the clamping potential was set to +50 mV and TER was evaluated 60 s later. (D) Without removing Ba²⁺, the clamping potential was returned to 0 mV and, after 20 s, TER was evaluated. (E) The apical compartment was rinsed several times with 75 mM KCl and TER was evaluated 10 min later. It can be seen that only tissues bathed on the inner surface by Na₂SO₄ Ringer's solution showed a marked increase of TER in response to the presence of Ba²⁺ in the apical compartment, an increase that is enhanced by the imposition of a +50-mV calming potential that favors the interaction of Ba²⁺ and SO₄ ²⁺ at the TJ level and the formation of BaSO₄ precipitate. n = 6.