Improving membrane voltage measurements using FRET with new fluorescent proteins


We used two new coral fluorescent proteins as fluorescence resonance energy transfer (FRET) donor and acceptor to develop a voltage sensor, named Mermaid, that displays 40% changes in emission ratio per 100 mV, allowing for direct visualization of electrical activities in cultured excitable cells. Notably, Mermaid has fast on-off kinetics at warm (33 °C) temperatures and can report voltage spikes comparable to action potentials.

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Figure 1: Development and kinetics of the voltage sensor Mermaid.
Figure 2: Depolarization patterns in cultured excitable cells expressing Mermaid visualized in single sweeps.


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We thank M. Higa and staff at Sesoko Marine Station of Ryuku University for their support during our excursions for sample collection. This work was partly supported by grants from Japan Ministry of Education, Culture, Sports, Science and Technology Grant-in-Aid for Scientific Research on priority areas, the Human Frontier Science Program and Special Postdoctoral Researcher Program of RIKEN.

Author information

S.K. developed mKOκ. H.T. performed experiments to develop mUKG and Mermaid. H.T. and Y.O. designed experiments in regard to VSD. H.T. and A.M. designed experiments with regard to fluorescent proteins and FRET. H.T. and A.M. wrote the paper. A.M. supervised this project.

Correspondence to Atsushi Miyawaki.

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Competing interests

S.K. is employed by Amalgaam. A.M. is a member of the scientific advisory board of Amalgaam. Amalgaam will sell mUKG and mKOκ

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Supplementary Figures 1–6, Supplementary Methods, Supplementary Table 1 (PDF 868 kb)

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Tsutsui, H., Karasawa, S., Okamura, Y. et al. Improving membrane voltage measurements using FRET with new fluorescent proteins. Nat Methods 5, 683–685 (2008) doi:10.1038/nmeth.1235

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