Table 2.

Comparison of time scales of rise, decay and full-width half-maximum (FWHM) duration of changes of intracellular Ca²⁺, extracellular glutamate (Glu) and ATP in astrocytes and neurons.

Signal	Origin	τrise [s]	τdecay [s]	FWHM [s]	Essential references
Ca2+	Astrocyte (soma)	2–20f	3–25f	5–160	Hirase et al., 2004; Nimmerjahn et al., 2004; Wang et al., 2006
	Astrocyte (soma)a	~0.5	~1.1	~2–4	Winship et al., 2007
	Neuron (soma)	2–5·10−3	0.1–0.4	~0.1–0.3	Svoboda et al., 1997; Waters et al., 2003; Nimmerjahn et al., 2004
	Astrocyte (process)	0.1–0.2	0.2–4f	~0.5–4	Di Castro et al., 2011; Panatier et al., 2011
	Neuron (presynaptic bouton)	0.5–5·10−3	~0.1–2	0.1–1*	Regehr et al., 1994; Emptage et al., 2001
Glu	Astrocyte	0.2–0.5	0.5–1.5	1–6	Domercq et al., 2006; Marchaland et al., 2008; Santello et al., 2011
	Neuron (synapse)	1–5·10−4	0.01–0.1	0.01–0.1*	Raghavachari and Lisman, 2004; Herman and Jahr, 2007; Okubo et al., 2010
ATP	Astrocyte	0.1–0.5	2–3	2–20	Pangršic et al., 2007; Li et al., 2008
	Neuron (synapse)	1–5·10−4*	0.2–1*	0.15–0.5	Dundwiddie and Masino, 2001; Pankratov et al., 2007

Glutamate and ATP values refer to transient increases of their extracellular concentrations following release in a Ca²⁺-dependent fashion. Therefore they describe the time course of the overall glutamate and ATP released by an exocytotic burst rather than by a single exocytotic event which can be much faster and occur within the first ~50 ms from Ca²⁺ rise (see text). Indicative rise and decay time constants as well as FWHM values are reported in terms of min–max ranges. Fast calcium signals imaging in astrocyte in the somatosensory cortex reported by Winship et al. (2007) are reported separately and dubbed by “a”. The letter “f” stands for values that were obtained by fitting of experimental data by a biexponential function such as f(t) = C·(exp(–t/τ_decay) – exp(–t/τ_rise)) with C being a proper scaling factor. Asterisk “

^*” denotes values estimated by a model of astrocytic and synaptic release introduced in De Pittà et al. (2011).