Calcium ion and the membrane potential of tumor cells.

Calcium ion affects ion permeability and membrane potential among many other aspects of cell function. Initial effects of increasing extracellular calcium upon membrane potential were studied in a quail fibrosarcoma (QT35) where calcium had a dose dependent effect, and normal quail fibroblasts, where there was little effect. Comparisons were then made in six different human hepatocellular carcinomas (Tong, HepG2, Hep3B, PLC/PRF/5, Mahlavu, and HA22T) in response to smaller changes in concentration. There were insignificant changes in membrane potential in two cell lines and significant elevations in four. Cytolysis by natural killer cells also declined in rough proportion to the increase in membrane potential. The less differentiated hepatocellular carcinoma cells have both higher baseline membrane potentials and a greater potential increase to increased calcium. By contrast, more highly differentiated tumor cells had paradoxically smaller membrane potentials and along with normal cells had small potential responses to calcium increases.