Chelating Intracellular Ca²⁺ Increases the Time Needed for the Recovery of the Vesicle Pool after High-frequency Stimulation

Abstract

To study the effects of calcium on the readily releasable vesicle pool in presynaptic cells of the crayfish neuromuscular junction, we used the drug EGTA-AM, an intracellular Ca²⁺ chelator. We measured the effects of Ca²⁺ on the cells' abilities to transmit nerve impulses by recording excitatory postsynaptic potentials (EPSPs), an indicator of vesicle release, both before and after a period of high-frequency stimulation. A cells vesicle pool was considered replenished when it regained its original EPSP amplitude. Our research shows that buffering intracellular Ca²⁺ decreases the cells' abilities to replenish vesicle supplies; it took longer for cells to recover from high-frequency stimulation and they did not appear to recover fully, even after several minutes.