Inhibition of the reverse mode of the Na⁺/Ca²⁺ exchanger does not affect EPSP amplitudes in the crayfish neuromuscular junction following periods of brief, high-frequency stimulation

Abstract

Calcium plays a major role in synaptic transmission in which it triggers the release of neurotransmitters into the synaptic cleft. The cell maintains low Ca²⁺ intracellular concentrations by various mechanisms including the Na⁺/ Ca²⁺ exchanger. This exchanger pumps out 1 Ca²⁺ ion in exchange for 3 Na+ ions. In some instances however the Na⁺/ Ca²⁺ is capable of functioning in the reverse mode, in which the exchanger pumps out 3 Na⁺ ions in exchange for 1 Ca²⁺ ion. We investigated the influence of exchangers reverse mode in synaptic facilitation. We inhibited the reverse mode of the Na⁺/ Ca²⁺ exchanger with the chemical KB-R7943. We induced synaptic facilitation in the presyanptic cell with a five second period of high-frequency stimulation of 20 Hz. However, we found no statistical difference in EPSP amplitude when the reverse mode of the Na⁺/ Ca²⁺ was inhibited compared to EPSP amplitudes without KB-R7943.