MATERIALS AND METHODS

Cells. CFPAC-1, CFPAC-PLJ-CFTR, and CFPAC-PLJ cells (Drumm et al., 1990) were obtained from Dr. R. Frizzell, University of Alabama at Birmingham. IB3-1 and S9 cells havebeen previously described (Egan et al., 1992). NIH 3T3-CFTR and 3T3-CFTR-AF508 cultures were ob-tained from Dr. M. J. Welsh, Universityof Iowa (Anderson et al., 1991b). A random culture of NIH 3T3 cells was purchased from the American Type Culture Collection (ATCC, Bethesda, MD).

Cell Culture Methods. CFPAC cells were grown in Iscove’s medium, supplemented with 10% heat-inactivated fetal calf serum, 100 units/mL penicillin, 100 ug/mL strep-tomycin, 0.25 Mg/mL fungizone, and 1%(w/v) glutamine. IB3 and S9 cells were grown in LHC-8 medium, supple-mented with 10% fetal calf serum, 100 units/mL penicillin, 100 wg/mL streptomycin, 0.25 ug/mL fungizone, and 1%(w/v) glutamine. 3T3 cells were grown in Eagle’s minimal essential medium (EMEM), supplemented with 10% adult bovine serum, 100 units/mL penicillin, 100 wg/mL streptomycin, 0.25 wg/mL fungizone, and 1%(w/v) glutamine. All culture materials were obtained fromBiofluids, Rockville, MD, and the osmolarity was 310 mosM. Prior to flux experiments, cells were split and seeded at low density on Costar 24-well plates in the respective medium for each cell line. After 5 h, the medium was replaced and the attached cells were allowed to grow to confluency during a period of 48-72 h at 37 Cin 5% C02/95% air. Measurement of36Cl Fluxes. Cells were loaded with 36C1~ as follows: Confluentcells were washed four times in their respective media. Following the last wash, 500 uh of medium containing approximately 1.4 x 10s cpm of 36C1~