Synaptic [Ca2+]: intracellular stores spill their guts

A critical role of Ca2+ in neuronal signaling is to couple electrical excitation to the activation of intracellular enzymes and signal transduction cascades. Presynaptically, action potential–mediated calcium influx releases neurotransmitter from presynaptic terminals. Postsynaptically, calcium ions play a crucial role in the induction of most forms of long-term synaptic potentiation (LTP) and depression (LTD), the putative cellular mechanisms of learning and memory; Ca2+ is required to regulate postsynaptic enzymes that trigger rapid modifications of synaptic strength and also to activate transcription factors that facilitate long-term maintenance of these modifications. How can a single second messenger system encode all of these functions with any kind of specificity? The answer is thought to lie in the details: with differences in amplitude, localization, and time course, different Ca2+ signals will carry very different biochemical meanings for the cell