Ca2+ plays a crucial role in cell communication. For example, periodical changes in Ca2+ concentration act as cell sig- nals. Intracellular Ca2+ signals have been measured by Ca2+ sensitive fluorescent dye . In this study, extracellular Ca2+ variation was monitored by a potentiometry using a solid-state type of Ca2+ Ion Selective Electrode (ISE). Ca2+ ISE had high sensitivity detecting down to 10-10M of calcium concentration, as well as high selectivity against K+. After KCl sti- mulus of cells in a microchannel, we observed an oscillating increase in Ca2+ concentration, associated with a periodic oscillation of cell activity (Hepatocyte, Hep2G).!