Simulation of the Na/sup +/-Ca/sup ++/ exchanger response to electrical and ionic stimulation in spherical-type cells

The Na/sup +/-Ca/sup ++/ exchanger plays a fundamental role in the regulation of the intracellular calcium concentration (Ca/sub i/) in several animal cell types, like axons, heart muscle, cardiac cells and reconstituted vesicles. It shows a dual operation, extruding or introducing Ca/sup ++/ through the cell membrane, depending on the electrochemical gradients, which in turn applies a membrane potential and ionic concentrations both inside and outside of the cell. We are interested on the dependence of calcium movement through the cell as well as the reversible behaviour of the exchanger. With the aid of a Ca/sup ++/ regulation simulator for spherical-type cells, 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 includes the diffusion process as a function of time in the cell, and the presence of a Ca/sup ++/ buffer (parvalbumin), both collaborating with the Na/sup +/-Ca/sup ++/ exchanger. This is only a part of the complete model that we have developed, because we were interested only in verifying the role of the exchanger during the presence of different Na/sup +/ and Ca/sup ++/ concentrations.