Model of intracellular calcium oscillations activated by inositol trisphosphate.

Transients or oscillations of intracellular free calcium concentration are general means for physiological intracellular signalling. Recently, it was shown that calcium ions modulate the InsP3 receptor/releasing calcium channel of the endoplasmic reticulum in a concentration dependent manner. Calcium either enhances (at low concentrations) or decreases (at high concentrations) the permeability of the channel activated by InsP3. A simple phenomenological model is proposed, based on these data. The model consists of two compartments. They are the cytoplasm and the endoplasmic reticulum with the calcium sequestering pump and the calcium release channel activated by InsP3. Parameters of the model are related to the experimentally measurable quantities. A qualitative analysis has shown that the hypothesis, which includes calcium modulation of the calcium releasing channel activated by InsP3, can explain all essential experimental findings. At least in cells with predominating calcium compartments with InsP3 sensitivity, this type of channel is compatible with mechanisms which generate repetitive calcium transients.