Solid symbols represent rhodamine 6G (R6G) venous effluent concentration in lungs after treatment with verapamil in protocol 2. Values are means ± SE (n = 6, 5, and 5 for loading phase, washing phase, and uncoupling phase, respectively). Open symbols represent R6G venous effluent concentration in lungs after treatment with verapamil in protocol 2 with DMSO (FCCP vehicle) instead of FCCP added to the perfusate during the uncoupling phase. Values are means ± SE (n = 2). Solid line is model fit to mean of the solid symbols. Dashed line is model prediction of the open symbols.