PHENOTYPICALLY AND KARYOTYPICALLY DISTINCT MADIN-DARBY CANINE KIDNEY-CELL CLONES RESPOND DIFFERENTLY TO ALKALINE STRESS

We isolated two cell clones from the wild-type Madin-Darby canine kidn ey cell line (MDCK) that resembles renal collecting duct epithelium. M orphology and karyotypes of the two cell clones were evaluated. The MD CK-C7 cell clone morphologically resembles principal cells (polygonal cell shape, flat), while the MDCK-C11 clone resembles intercalated cel ls (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. Transfo rmed MDCK-C7F cells are characterized by two abnormal (biarmed) chromo somes. In contrast, MDCK-C11 cells are not phenotypically altered by a lkaline stress. In order to elucidate the role of intracellular pH (pH (i)) in the transformation process, we measured pH(i) under control co nditions (pH 7.4), after 5 min exposure to alkaline stress (''acute ex periment,'' pH 7.7) and after incubation of the cells in alkaline medi um for two weeks (''chronic experiment,'' pH 7.7). Under control condi tions, MDCK-C7 cells maintained pH(i) at 7.14 +/- 0.01 (n = 154) and M DCK-C11 cells at 7.01 +/- 0.01 (n = 147). Acute alkaline stress increa sed pH(i) of both cell types to similar steady-state values. Under chr onic alkaline stress, MDCK-C7 cells were unable to maintain intracellu lar pH within normal limits exhibiting sustained alkalinization, where as MDCK-C11 cells could successfully regulate pH(i). We conclude that wild-type MDCK cells consist of two genetically distinct subpopulation s with different morphology and function. Only the MDCK-C7 clone that resembles the principle cell type of renal collecting duct can be tran sformed by alkaline stress while the MDCK-C11 clone resists this treat ment, due to efficient pH(i) control mechanisms. (C) 1995 Wiley-Liss, Inc.