The CA²⁺/ATPase Pump in the Endoplasmic Reticulum Affects EPSP Amplitudes and Synaptic Facilitation at the Crayfish Neuromuscular Junction

Abstract

There are four mechanisms that remove Ca²⁺ from the presynaptic nerve terminal following an action potential. They are: the Na²⁺/Ca²⁺ exchanger, the Ca²⁺/ATPase pump in the mitochondria, the Ca2+/ATPase pump in the plasma membrane, and the Ca²⁺/ATPase pump in the endoplasmic reticulum (E.R.). The objective of this experiment was to investigate the importance of the Ca²⁺/ATPase pump in the E.R. in removing Ca²⁺ from the cell.We tested the relative importance of this pump by measuring excitatory post synaptic potential (EPSP) amplitudes and synaptic facilitation. To do this, we compared normal twin pulse facilitation to twin pulse facilitation in crayfish under the effects of Ochratoxin A, a drug that enhances the functioning of the Ca²⁺/ATPase pump and twin pulse facilitation in the presence of BHQ, a drug that inhibits the functioning of the Ca²⁺/ATPase pump. We found that Ochratoxin A has a depressive effect on both EPSP amplitude and synaptic facilitation, while BHQ had the opposite effect. Our results indicate that the Ca²⁺/ATPase pump in the E.R. plays a significant role in regulating the amount of residual Ca²⁺ in the presynaptic nerve terminal.