Validation of a Na/sup +/-Ca/sup ++/ regulation model for high variations of the inner cell conditions

The Na/sup +/-Ca/sup ++/ exchanger is a reversible regulation mechanism which can work to deplete or augment the internal Ca/sup ++/ concentration, as long as there is enough free Na/sup +/. A Ca/sup ++/ regulation simulator has been demonstrated to be reliable for simulating the cell response to ionic and electrical stimuli, providing the internal Ca/sup ++/ concentration is in the physiological range at the beginning of the simulation. In this paper, we pose several corrections to the original model and we also discuss the inclusion of additional kinetic and sensitivity parameters of the mechanisms in order to follow the biological role of the exchanging current.