Ouabain‐resistant human lymphoblastoid lines altered in the (Na+ + K+)‐dependent ATPase membrane transport system

Abstract

Diploid human lymphoblastoid cells with altered response to ouabain inhibition of the (Na⁺ + K⁺)‐dependent ATPase transport system, manifest both in whole cells and in purified plasma membrane vesicles, were selected for their resistance to 0.1 m̈M ouabain. Ouabain‐resistant (OUA^R) cells with normal growth at 50 times this dose were recovered at a frequency of 1 × 10⁻⁶. This frequency was increased 9‐fold after exposure to ethyl methane sulphonate but was decreased by the frameshift mutagen ICR‐191, under conditions where both increased the frequency of 8‐azaguanine‐resistant colonies. The ouabain resistance phenotype was stable after 200 population doublings in the absence of ouabain. OUA^R clones showed 30–50% of the wild type amount of ³H‐ouabain bound per cell, with the same dissociation constant for ouabain, 0.1 m̈M at 0.5 mM K⁺, as observed in wild‐type cells. Both the initial rate of uptake of ⁸⁶Rb⁺ in OUA^R cells and the (Na⁺ + K⁺)‐dependent ATPase activity of OUA^R plasma membranes showed decreased sensitivity to ouabain inhibition. However, growth and transport properties of OUA^R cells in the absence of ouabain were unchanged compared with wild type cells.