Reducing Extracellular Sodium Concentration Decreases Synaptic Facilitation

Abstract

We examined how decreasing the concentration of external sodium affects synaptic facilitation via the Sodium/Calcium exchanger (NCX). The NCX brings three sodium ions into the cell, and transfers one calcium ion out of the cell. Previous experiments have manipulated the NCX by decreasing extracellular sodium which led to increased synaptic facilitation. It has been shown that synaptic facilitation can lead to enhanced learning and memory, which makes it important to further understand the role of the NCX in synaptic facilitation. Based on these experiments, we hypothesized that a decrease in concentration of external sodium will increase synaptic facilitation by reducing the function of the NCX. In order to decrease the concentration of external sodium, normal crayfish Ringers solution was mixed with sodium-free crayfish Ringers solution, which was kept isosmotic by replacing sodium with choline, using differing ratios to create differing sodium concentrations. Intracellular recording and twin pulses were used to elicit and record EPSPs. The results refuted our hypothesis, showing that as extracellular sodium decreases, synaptic facilitation decreases. These results are contrary to most previous experiments regarding the NCX and facilitation, but they do show a correlation between the NCX and facilitation.