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 extrace llular calcium upon membrane potential were studied in a quail fibrosa rcoma (QT35) where calcium had a dose dependent effect, and normal qua il fibroblasts, where there was little effect. Comparisons were then m ade in six different human hepatocellular carcinomas (Tong, HepG2, Hep 3B, PLC/PRF/5, Mahlavu, and HA22T) in response to smaller changes in c oncentration. There were insignificant changes in membrane potential i n two cell lines and significant elevations in four. Cytolysis by natu ral killer cells also declined in rough proportion to the increase in membrane potential. The less differentiated hepatocellular carcinoma c ells have both higher baseline membrane potentials and a greater poten tial increase to increased calcium. By contrast, more highly different iated tumor cells had paradoxically smaller membrane potentials and al ong with normal cells had small potential responses to calcium increas es.