Mechanisms underlying spontaneous calcium spiking in aequorin-loaded ROS 17/2.8 cells

In earlier studies, McLeod and coworkers reported the detection of spontane ous calcium spiking in ROS 17/2.8 cells which they suggested was derived fr om individual cells progressing through mitosis or the cell cycle. They als o indicated that the degree of spiking could be modulated by exposure of th e cells to time-varying extremely low frequency electric fields. Given the implications of such observations for our understanding of the effects of e lectromagnetic fields on biological systems, it appeared important for mech anistic reasons to understand the basis of this spiking. In this study, we were able to confirm that spontaneous calcium spiking activity could be det ected in ROS 17/2.8 cells and that this appeared to emanate from individual cells. We found this spiking to be completely dependent on extracellular c alcium ions and to be independent of the inositol 1,4,5-trisphosphate-sensi tive intracellular calcium store. This spiking is not reduced by treatments which slow down or block the passage of cells through the cell cycle. Furt her, we found that spiking was only detectable in the most highly aequorin- loaded subpopulation of cells whose growth rate is reduced and whose morpho logical appearance is abnormal. In conjunction with what is known about cal cium spiking in other, nonexcitable mammalian cells in culture, the data pr esented strongly argue that the spontaneous calcium spiking observed in ROS 17/2.8 cells is unrelated to normal events of the cell cycle and most like ly result from the damaging effects of excessive loading with aequorin. (C) 2000 Wiley-Liss, Inc.