MDCK-OAT-K2 cells were preincubate at 37°C for 20 min either in normal, Na⁺-free, or Cl⁻-free medium as described in the text and incubated at 37°C for 5 min with taurocholate (250 nM, 32.0 kBq/ml) in the absence (total) or presence (nonspecific) of 500 μM unlabeled taurocholate (2 ml; pH 7.4). Each value represents the mean ± S.E. of three experiments.