Calcium sparks in mouse ventricular myocytes at physiological temperature

Area of Science:

• Cardiology
• Molecular Biology
• Physiology

Background:

• Calcium (Ca2+) sparks are fundamental units of Ca2+ release from the sarcoplasmic reticulum in cardiac muscle.
• Previous studies on Ca2+ spark characteristics were primarily conducted at room temperature, limiting understanding of physiological conditions.

Purpose of the Study:

• To compare the characteristics of spontaneous Ca2+ sparks in mouse ventricular myocytes at physiological (37°C) and room (22°C) temperatures.
• To investigate the influence of temperature on Ca2+ spark incidence, frequency, amplitude, kinetics, and spatial properties.

Main Methods:

• Utilized fluo-3 fluorescence imaging to detect Ca2+ sparks in isolated resting mouse ventricular myocytes.
• Employed field stimulation and fura-2 imaging to assess Ca2+ transients and concentrations under different temperatures.
• Manipulated sarcoplasmic reticulum (SR) Ca2+ content via superfusion to evaluate its role in temperature-dependent spark changes.

Main Results:

• Ca2+ spark incidence and frequency were significantly lower at 37°C compared to 22°C.
• Spark amplitudes and times to peak were reduced at 37°C, while spatial width and decay times remained unchanged.
• Sarcoplasmic reticulum Ca2+ content decreased significantly at 37°C, and restoring SR Ca2+ did not reverse temperature-induced changes in spark parameters.

Conclusions:

• Temperature affects Ca2+ spark frequency, likely by altering SR Ca2+ stores.
• Changes in spark amplitude and rise time at physiological temperatures may be attributed to temperature-dependent modulation of ryanodine receptor function.
• Findings highlight the importance of temperature in understanding cardiac Ca2+ handling and spark dynamics.