Effect of Lowered Extracellular Sodium Concentration on Sodium/Calcium Exchanger and EPSPs

Abstract

On a cellular level, simple learning processes are a result of facilitation of postsynaptic excitatory potentials (EPSPs). Facilitation occurs because of the presence of residual calcium in a presynaptic neuron, and various cell mechanisms regulate this amount, one of them being the sodium-calcium exchanger. In its forward state of action, the exchanger pumps calcium ions out, and in its reverse stage, it pumps calcium ions in. The working of the exchanger is dependent on the concentration and electrical gradients across the membrane; it flips from the forward state to the reverse stage when the cell membrane gets depolarized (during action potential). We decreased the extracellular sodium ion concentration to 75% of its original value in order to observe how that would affect facilitation. We failed to get any conclusive answers to the question because we did not have reliable control data to compare with, and thus were unable to make any judgments about whether facilitation increased or decreased in the experimental case with 75% Na. But we were able to verify the hypothesis that blocking the reversal of the exchanger leads to less facilitation, which has already been shown by previous studies.