Spontaneous network activity visualized by ultrasensitive Ca(2+) indicators, yellow Cameleon-Nano.

We report ultrasensitive Ca(2+) indicators, yellow cameleon-Nano (YC-Nano), developed by engineering the Ca(2+)-sensing domain of a genetically encoded Ca(2+) indicator, YC2.60 or YC3.60. Their high Ca(2+) affinities (K(d) = 15-140 nM) and large signal change (1,450%) enabled detection of subtle Ca(2+) transients associated with intercellular signaling dynamics and neuronal activity, even in 100,000-cell networks. These indicators will be useful for studying information processing in living multicellular networks.