Transients in global Ca2+ concentration induced by electrical activity in a giant nerve terminal


  • This review was presented at The Journal of Physiology Symposium entitled Size matters: formation and function of GIANT synapses, which took place at the Annual meeting of the Society for Neuroscience, New Orleans, LA, USA on 12 October 2012. It was commissioned by the Editorial Board and reflects the views of the authors.

E. Neher: Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Göttingen, Germany. Email:


Abstract  Giant nerve terminals offer a unique opportunity to learn about dynamic changes in intracellular global Ca2+ concentration ([Ca2+]i) because this quantity can be measured precisely with indicator dyes and the composition of the intra-terminal ionic milieu can be controlled. We review here recent literature on [Ca2+]i signalling in the calyx of Held and discuss what these measurements can tell us about endogenous Ca2+ buffers and Ca2+ extrusion mechanisms. We conclude that in spite of the favourable experimental conditions, some unresolved questions still remain regarding absolute values for the Ca2+-binding ratio, the affinity of the basic fixed buffer and the Ca2+ affinities of the major endogenous Ca2+ binding proteins. Uncertainties about some of these presynaptic properties, including the roles of Mg2+ and ATP (as a Mg2+ buffer), however, extend to the point that mechanisms controlling the decay of [Ca2+]i signals in unperturbed terminals may have to be reconsidered.