Spatial Ca(2+) distribution in contracting skeletal and cardiac muscle cells

Area of Science:

• Muscle physiology
• Cellular biology
• Calcium signaling

Background:

• Intracellular calcium (Ca2+) dynamics are crucial for muscle contraction.
• Understanding the spatiotemporal distribution of Ca2+ release is key to muscle function.
• Previous techniques faced limitations in resolving rapid Ca2+ events in contracting cells.

Purpose of the Study:

• To define the spatiotemporal distribution of intracellular Ca2+ release in contracting skeletal and cardiac muscle cells.
• To compare Ca2+ release patterns between skeletal and cardiac muscle at the subsarcomeric level.
• To investigate the factors contributing to differences in Ca2+ release dynamics.

Main Methods:

• Utilized a snapshot imaging technique with Rhod-2 fluorescence.
• Performed calcium imaging on intact skeletal and cardiac muscle cells during action potential-induced contractions.
• Minimized motion artifacts using a brief (7 ns) excitation light pulse.

Main Results:

• Skeletal muscle exhibited a rapid (peak < 3 ms) Ca2+ transient with distinct subsarcomeric Ca2+ gradients within the first 4 ms.
• Cardiac muscle displayed a slower Ca2+ transient (peak ~100 ms) without detectable subsarcomeric Ca2+ gradients.
• Theoretical simulations supported that rapid, synchronous Ca2+ release in skeletal muscle enables gradient detection.

Conclusions:

• Significant differences exist in the speed and synchrony of local Ca2+ release between skeletal and cardiac muscle.
• Subsarcomeric Ca2+ gradients are detectable in skeletal muscle due to rapid, synchronized release.
• Absence of detectable gradients in cardiac muscle is attributed to slower, asynchronous recruitment of release units.