Calmodulin kinase modulates Ca2+ release in mouse skeletal muscle

Area of Science:

• Muscle physiology
• Cellular signaling
• Biochemistry

Background:

• Skeletal muscle contraction relies on calcium (Ca2+) release from the sarcoplasmic reticulum (SR).
• Calmodulin kinase II (CaMKII) phosphorylation influences SR Ca2+ release proteins in vitro.
• The in vivo role of CaMKII in intact muscle remains unclear.

Purpose of the Study:

• To investigate the role of CaMKII-induced phosphorylation in regulating intracellular calcium levels ([Ca2+]i) and force production in intact skeletal muscle fibers.
• To determine if CaMKII affects basal SR Ca2+ release, SR Ca2+ uptake, or the force-Ca2+ relationship.

Main Methods:

• Single fast-twitch mouse skeletal muscle fibers were isolated.
• CaMKII activity was inhibited by injecting a CaMKII inhibitory peptide.
• Intracellular Ca2+ ([Ca2+]i) and muscle force were measured during various stimulation patterns.
• An inactive control peptide was used as a control.

Main Results:

• CaMKII inhibition significantly reduced tetanic [Ca2+]i by approximately 25%.
• CaMKII inhibition did not affect the rate of SR Ca2+ uptake or the force-Ca2+ relationship.
• Repeated tetanic stimulation normally increases tetanic [Ca2+]i, but this increase was attenuated by CaMKII inhibition.

Conclusions:

• CaMKII-induced phosphorylation plays a crucial role in facilitating SR Ca2+ release in skeletal muscle.
• This phosphorylation enhances basal Ca2+ release and contributes to the rise in [Ca2+]i during repeated contractions.
• CaMKII activity establishes a positive feedback loop between [Ca2+]i and SR Ca2+ release, optimizing muscle function.