Mitochondria regulate the amplitude of simple and complex calcium oscillations.

In a mathematical model for simple calcium oscillations [Biophys. Chem. 71 (1998) 125], it has been shown that mitochondria play an important role in the maintenance of constant amplitudes of cytosolic Ca(2+) oscillations. Simple plausible rate laws for Ca(2+) fluxes across the inner mitochondrial membrane have been used in this model. Here we show that it is possible to use the same rate laws as a plug-in element in other existing mathematical models and obtain the same effect on amplitude regulation. This result appears to be universal, independent of the type of model and the type of Ca(2+) oscillations. We demonstrate this on two models for spiking Ca(2+) oscillations [J. Biol. Chem. 266 (1991) 11068; Cell Calcium 14 (1993) 311] and on two recent models for bursting Ca(2+) oscillations; one of them being a receptor-operated model [Biophys. J. 79 (2000) 1188] and the other one being a store-operated model [BioSystems 57 (2000) 75].

Influence of an external electric field on structure in surface-stabilized smectic-C chevron cells

We use a Landau-de Gennes model to study the effect of static external electric fields on the director and layer structure and switching in surface stabilized smectic-C cells with uniform chevron structure. We consider uniform switching of the whole cell and find the threshold electric field needed to switch the director from one stable state to the other stable state. The effect of temperature and cell thickness on the value of the threshold electric field is studied. We also find the switching time as a function of the strength of the applied electric field and study the director and layer structure during the switch.