Cardiac mechanical restitution in active and hibernating Richardson's ground squirrel

Area of Science:

• Cardiovascular Physiology
• Comparative Physiology
• Hibernation Biology

Background:

• Cardiac mechanical restitution is crucial for maintaining heart function under varying conditions.
• Hibernation involves significant physiological adaptations, including changes in cardiac function.

Purpose of the Study:

• To compare cardiac mechanical restitution in papillary muscles of active and hibernating Richardson's ground squirrels.
• To investigate the role of external calcium concentration ([Ca2+]o) and sarcoplasmic reticulum (SR) calcium release in cardiac function during hibernation.

Main Methods:

• Papillary muscle preparations from active and hibernating Richardson's ground squirrels were used.
• Cardiac mechanical restitution was assessed at varying external calcium concentrations (0.1, 2.8, 5 mM) and temperatures (37, 20, 7 degrees C).
• The effect of ryanodine on postrest potentiation was evaluated.

Main Results:

• Hibernating squirrels exhibited significantly higher restitution amplitude across all tested conditions.
• Pause duration for maximal first postrest contraction (F1) differed, being shorter in hibernating animals at 37 degrees C but longer at 7 degrees C.
• Ryanodine significantly inhibited postrest potentiation, more so in hibernating animals, indicating greater dependence on SR calcium release.

Conclusions:

• Cardiac excitation-contraction coupling in both states relies heavily on SR calcium release.
• Hibernation intensifies the dependence on ryanodine-sensitive SR calcium channels for cardiac function.
• Cardiac mechanical restitution sensitivity to external calcium concentration remains similar between active and hibernating states.