The na-ca exchanger plays a fundamental role in the regulation of the intracellular Calcium concentration (cai) in several animal cell types like axons, heart muscle, cardiac cells and reconstituted vesicles. It shows a dual operation, extruding or introducing ionca through the cell membrane, depending on the electrochemical gradients, which in turn implies membrane potential and ionic concentrations inside and outside of the cell {carafoli}.We are interested on the dependence of Calcium movement through the cell as well as the reversible behavior of the exchanger. Then, with the aid of a previously reported ionca--regulation simulator for spherical-type cell cbms99, where we can apply the stimuli at the membrane level, we have been able to verify the presence of inward--outward exchanging currents. Our model then includes the diffusion process along the time in the cell, and the presence of an ionca buffer (parvalbumin), both collaborating with the na-ca exchanger. It is only a part of the complete model we have developed before {laura1, laura2, and cbms99} because we were interested only in verifying the role of the exchanger during the presence of different Na and ionca concentrations.We follow the experimental protocols proposed by Miura and Kimura, 1989, to induce outward and inward currents by means of an ionic pulse. Then, we simulated the application of a voltage pulse to investigate the interaction between Ca++ Channels, Na-Ca Exchanger and parvalbumin. The former simulations are included for comparing the behavior of our na-ca exchanger model, so we only used these equations, along with the model for the buffer and the passive diffusion. Nevertheless, the latter one is included to give the reader a complete idea of the collaboration of the na-ca exchanger and the ionca voltage-gated channels. It has to be mentioned that the duration of each simulation were selected to emulate the experimental protocols of Miura et al., as we explained above, except for those corresponding to the voltage pulse, where the time were defined to give a good idea of temporal behavior of each transporting mechanism.We verify that the increase of extra cellular Sodium ion concentration (nao), could induce a ionca extrusion (Inward current) similar to the one produced by a voltage pulse, and in the same way, that it is possible to induce the entrance of ionca if cao is elevated (Outward current). In both cases the concentration of the coupled ion, nai and nao respectively, determines the value of the maximum current density, as mentioned by lauger. We also observed that if nao is tends to zero, the outward current increases rapidly, and in the same manner, if nai is decreased, the inward current is also higher; these tests are not shown.We also agree with experimental results establishing that the na-ca exchanger: Is strongly dependent on the holding membrane potential, Has a large time constant (higher than the channel current one, It is a reversible system, Is also strongly dependent on the ionic concentrations of ionca and na, because they define the energy barrier to traverse in the exchanging, and It has an exponential behavior.