Spontaneous Neurotransmitter Release Depends on Intracellular Rather than ER Calcium Stores in Cultured Xenopus NMJ

Calcium ions are important in many vital neuron processes, including spontaneous neurotransmitter release. Extracellular calcium has long been known to be related to spontaneous neurotransmitter release, but the detailed mechanism for the effect of intracellular Ca2+ on synaptic release has not yet been understood. In this research, 1,2-bis-(o-aminophenoxy)-ethane-N, N, N', N'-tetraacetic acid tetraacetoxy-methyl ester (BAPTA-AM) was used to combine with cytosolic free Ca2+ in a calcium free medium of cultured Xenopus neuromuscular junctions (NMJ). The spontaneous synaptic current (SSC) frequency was obviously reduced. Then, drugs were applied to interrupt and activate the Ca2+ release channels in the endoplasmic reticulum (ER) membrane, but the SSC frequency was not affected. The results show that spontaneous neurotransmitter release depends on intracellular rather than ER calcium in cultured Xenopus NMJ without extracellular calcium.