| Summary: | The concentration of free cytosolic Ca2+ 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 Ca2+ concentration. We have previously studied how Ca2+ influx across the plasma membrane affects the period and shape of Ca2+ oscillations in HEK293 cells. However, our theoretical work was unable to explain how the shape of Ca2+ 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 Ca2+ to the production and degradation of inositol trisphosphate.
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