Different changes in transmembrane potential of cultured cells after ouabain-inhibited active Na+/K+-transport

The inhibition of (Na+/K+) activated membrane ATPase by cardiac glycosides is electrophysiologically detectable in terms of a reduction of the transmembrane potential (TMP) of cells. Two hours after incubation in medium with 10(-4) mole/l ouabain added, the TMP of cells were measured by means of glass microelectrodes. Compared with untreated controls, HeLa and FL-cells, human embryo cells, skin fibroblasts, leukocytes, and exudate macrophages without exception showed a TMP reduction typical of the particular cell kind. Primary cultures of human embryo cells and skin fibroblasts revealed the highest sensitivity (approx. 60% TMP reduction), while lesser and relatively low sensitivities were observed for permanent cells (approx. 30% TMP reduction) and white blood cells (approx. 20% TMP reduction), respectively. Unlike the above, the ovarian tumor cells showed inter-individually varied reactions within the range of TMP changes from - 55% to + 33%. The majority of malignant tumours, in particular, exhibited only a weak reaction in the ouabain test or no reaction at all. On the other hand, ovarian cysts or other clinically benign tumors showed the normal ouabain effect. The experimental results obtained for the ovarian tumors are believed to demonstrate a defect of one or several transport enzymes, which effect is associated with the malignancy of cells and may be used as a functional in vitro marker for malignancy in the field of cell physiology.