Calcium Detection

Using the Biofluorometer with Muscle Physiology Research systems

The use of fluorescence for sensing and imaging of the cellular signaling pathways has emerged as an indispensable tool in modern physiology, providing dynamic information of quantity and localization of the molecules of interest. Using appropriate indicator dyes, molecules alter their fluorescent characteristics in response to ion binding or membrane integration, so that the optical signal from the indicator can be measured to monitor the amplitude and the time course of various metal ions like Na⁺, K⁺, Mg²⁺ and Ca²⁺, as well as pH and membrane potential, in cellular compartments.

A specific target molecule like Ca²⁺ is responsible for many physiological functions, such as neurotransmitter release, fertilization and ion channel functions. Studying the cellular channel functions is directly related to the transient increase in the myoplasmic free calcium concentration (Δ[Ca²⁺]), as a key intermediate signaling event between excitation and contraction of muscle fibers. This makes it essential for the analysis of the force development in muscles.

The concomitant assessment of both parameters simultaneously is therefore critical in the evaluation and interpretation of the force development characteristics of single muscle fibers. Fluorescence techniques used in conjunction with muscle research systems (like WPI’s  SI-HTB2 or SI-CTS200) to record muscle force has therefore become a standard technique in cardiac muscle and skeletal muscle physiology. WPI’s Biofluorometer (SI-BF-100) was specifically developed to monitor rapid changes, e.g. in Δ[Ca²⁺], using high-power LED modules, optical fiber combiner and highly sensitive photomultiplier modules to detect even very weak fluorescent signals at sample rates of 1,000 ratios/s.

The Biofluorometer opens a wide field in functional fluorescence research, by studying the fundamental and/or applied aspects of the underlying energetics and signaling aspects of muscle contraction. This is notably useful in:

Pre-clinical & toxicological studies:

• Screening of potential drugs
• Evaluating models of cardiac disease
• Evaluating the effects of muscle dystrophies/myopathies

Sports & rehabilitation:

• Disuse vs. overuse
• Muscle damage
• Functioning of transplanted heart

Future application of the SI-BF-100 may include the study of:

• Golgi organs and endoplasmic reticulum (ER)
• Protein detection and quantification
• Na⁺, K⁺, Mg²⁺ signaling pathways
• Brain function in neuroscience
• Genetically-encoded fluorophores in optogenetics
• Insulin signaling pathways in experimental nutrition
• Oncology

References in the field of application

1. Belz, et al., Fiber Optic Biofluorometer for Physiological Research on Muscle Slices. Proc SPIE 9702, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XVI, 2016.
2. Ueno, et al., Fluorescent probes for sensing and imaging. Nature 8, 642-645, 2011.
3. Baylor, et al., Intracellular calcium movements during excitation–contraction coupling in mammalian slow-twitch and fast-twitch muscle fibers. Brief Review. J Gen Physiol 139, 261–272, 2012.
4. Baylor, et. al., Measurement and interpretation of cytoplasmic [Ca2+] signals from calcium-indicator dyes. News Physiol Sci 15, 19-26, 2000.