Ca(2+)-dependent negative control mechanism for Ca(2+)-induced Ca2+ release in crayfish muscle

Area of Science:

• Muscle physiology
• Calcium signaling
• Cellular mechanisms

Background:

• Calcium-induced calcium release (CICR) is crucial for muscle contraction.
• The termination mechanism of CICR is not fully understood.
• Investigating CICR termination provides insights into muscle function and dysfunction.

Purpose of the Study:

• To elucidate the mechanism of rapid termination of Ca(2+)-induced Ca(2+) release (CICR) in crayfish muscle fibers.
• To determine if CICR termination is influenced by calcium current inactivation or sarcoplasmic reticulum calcium depletion.
• To identify factors regulating the speed of CICR termination.

Main Methods:

• Voltage-clamped crayfish muscle fibers loaded with the calcium indicator rhod-2.
• Depolarizing voltage steps to evoke calcium currents (ICa) and subsequent Ca(2+) release.
• Varying ICa inactivation rates and sarcoplasmic reticulum (SR) Ca(2+) load.
• Using voltage ramps to alter ICa onset speed.
• Pre-elevating intracellular Ca(2+) to assess its effect on release.

Main Results:

• CICR rapidly terminated within approximately 6 ms, independent of ICa inactivation or SR Ca(2+) depletion.
• Pre-elevated intracellular Ca(2+) depressed subsequent CICR.
• Faster ICa onset led to greater Ca(2+) release, even with similar current amplitudes.
• These findings indicate a Ca(2+)-dependent negative feedback mechanism.

Conclusions:

• A Ca(2+)-dependent negative control mechanism rapidly terminates CICR.
• This termination occurs independently of the trigger ICa duration.
• The mechanism operates before significant SR Ca(2+) depletion, suggesting a rapid feedback loop.