Calcium near the release site is essential for basal ACh release in Xenopus.

Extracellular calcium is essential for neurotransmitter release, but the detailed mechanism by which Ca2+ regulates basal synaptic release has not yet been fully explored. In this study, calcium imaging and the whole-cell patch-clamp technique were used to investigate the role of Ca2+ in basal acetylcholine (ACh) release in the Xenopus neuromuscular junction and in isolated myocytes exogenously loaded with ACh. Carried out in normal and Ca2+-free extracellular solution, the results indicate that Ca2+ near the release site is essential for basal neurotransmitter release.