Ratio-metric measurement of intracellular calcium in visceral muscles via selective expression of a yellow cameleon calcium sensor

Chiho Takai, Naoko Iwata, Kazunori Kanemaru, Kenji F. Tanaka, Yao Yu, Satoshi Iino, Shinsuke Nakayama

Research output: Contribution to journalArticlepeer-review


Visceral muscles exhibit various patterns of contractions depending on their locations and functions. Most visceral muscles are comprised of smooth muscle, and an increase in the intracellular Ca2+ concentration ([Ca2+]i) induces contraction, as in striated muscle. In order to critically assess the mechanisms underlying a variety of visceral movements, it is important to measure [Ca2+]i. However, due to limitations of sensing methods, it is difficult to compare [Ca2+]i between different organs and individuals. In this study, we thus measured [Ca2+]i in visceral muscles using transgenic mice that selective expressed a genetically encoded ratiometric Ca2+ indicator (YC-Nano50) in both skeletal and smooth muscles. We acquired CFP and YFP fluorescence images of YC-Nano50 separately, to evaluate the fluorescence resonance energy transfer (FRET), which reflects [Ca2+]i. In the resting condition, the YFP/CFP ratio measured in isolated muscularis was lower in smooth muscle than in skeletal muscle, corresponding to [Ca2+]i in the range of approximately 20–40 nM and 50–80 nM, respectively. Among visceral smooth muscles, the YFP/CFP ratio was highest in the urinary bladder, and lowest in the stomach (antrum). In the esophagus, comprised of skeletal muscle, the YFP/CFP ratio was higher than in other visceral smooth muscles, and was comparable to that in abdominal wall and diaphragm skeletal muscles. In addition, we were able to measure Ca2+ transients and oscillations in muscle sheets and intact segments isolated from the intestine even during movement. This method is able to elucidate the biological significance of Ca2+ signaling in diverse functions of visceral muscles.

Original languageEnglish
Article number131756
JournalSensors and Actuators B: Chemical
Publication statusPublished - 2022 Aug 1


  • Fluorescence resonance energy transfer (FRET)
  • Gastrointestinal tract
  • Quantitative calcium measurement
  • Resting calcium concentration
  • Smooth muscle
  • Visceral muscle

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Instrumentation
  • Condensed Matter Physics
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Electrical and Electronic Engineering
  • Materials Chemistry


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