Cell calcium oscillations: the origin of their variability.

Oscillation in calcium levels in the cytoplasm of individual cells has been observed experimentally to consist of a series of spikes and plateaux of differing amplitudes and inter-peak intervals. On the other hand, mathematical models based on known biochemical reaction kinetic behaviours predict, in the main, limit cycle behaviour. Chaotic solutions do not mimic the observed variability, and so another solution was sought by the introduction of filtered noise into some of the kinetic coefficients. Some of the variability can be predicted from this mechanism, but it is likely that other sources contribute to this as well.