Calcium oscillations in HEK293 cells lacking SOCE suggest the existence of a balanced regulation of IP production and degradation.

The concentration of free cytosolic Ca is a critical second messenger in almost every cell type, with the signal often being carried by the period of oscillations, or spikes, in the cytosolic Ca concentration. We have previously studied how Ca influx across the plasma membrane affects the period and shape of Ca oscillations in HEK293 cells. However, our theoretical work was unable to explain how the shape of Ca oscillations could change qualitatively, from thin spikes to broad oscillations, during the course of a single time series. Such qualitative changes in oscillation shape are a common feature of HEK293 cells in which STIM1 and 2 have been knocked out. Here, we present an extended version of our earlier model that suggests that such time-dependent qualitative changes in oscillation shape might be the result of balanced positive and negative feedback from Ca to the production and degradation of inositol trisphosphate.