Phenotypically and karyotypically distinct Madin‐Darby canine kidney cell clones respond differently to alkaline stress

Abstract

We isolated two cell clones from the wild-type Madin-Darby canine kidney cell line (MDCK) that resembles renal collecting duct epithelium. Morphology and karyotypes of the two cell clones were evaluated. The MDCK-C7 cell clone morphologically resembles principal cells (polygonal cell shape, flat), while the MDCK-C11 clone resembles intercalated cells (cuboidal cell shape, high). The diploid chromosome number of MDCK-C7 cells is 83.1 ± 0.2 (n = 139); that for MDCK-C11 cells is 78.8 ± 0.1 (n = 128). Culture of MDCK-C7 cells in alkaline medium (pH 7.7) induced irreversible phenotypical and genotypical alterations. transformed MDCK-C7F cells are characterized by two abnormal (biarmed) chromosomes. In contrast, MDCK-C11 cells are not phenotypically altered by alkaline stress. In order to elucidate the role of intracellular pH (pH_i) in the transformation process, we measured pH_i under control conditions (pH 7.4). after 5 min exposure to alkaline stress (“acute experiment,” pH 7.7) and after incubation of the cells in alkaline medium for two weeks (“chronic experiment,” pH 7.7). Under control conditions, MDCK-C7 cells maintained pH_i at 7.14 ± 0.01 (n = 154) and MDCK-C11 cells at 7.01 ± 0.01 (n = 147). Acute alkaline stress increased pH_i of both cell types to similar steady-state values. Under chronic alkaline stress, MDCK-C7 cells were unable to maintain intracellular pH within normal limits exhibiting sustained alkalinization, whereas MDCK-C11 cells could successfully regulate pH_i. We conclude that wild-type MDCK cells consist of two genetically distinct subpopulations with different morphology and function. Only the MDCK-C7 clone that resembles the principle cell type of renal collecting duct can be transformed by alkaline stress while the MDCK-C11 clone resists this treatment, due to efficient pH_i control mechanisms.