Scientists have discovered a new mechanism in cells that aids the mammal's heart to keep in tune with the circadian rhythms. This discovery could help explain why some people are more at risk for developing cardiac problems.
Circadian rhythms regulate the time-based systems of the body around a 24-hour cycle. They affect sleep and waking, our metabolism, and our cognitive processes.
Since long ago, it has been known that the heart is affected by this biological clock. People have a higher heart rate when they wake up in the morning and a lower rate when they sleep at night.
It is still a mystery how the heart allows for these changes throughout the day. The heart transmits signals to the nervous system. However, scientists from the MRC Laboratory for Molecular Biology (University of Cambridge) have made a breakthrough in understanding how the cell level can also shift gears independently.
A new paper by Alessandra Stigherlin (first author) and circadian biologist Alessandra Stegherlin reveals that mice's heart cells have an ion transport mechanism that allows them to alter the concentrations of potassium (K), salt (Na), and chloride ions. This is in response to changing levels of proteins.
This mechanism allows heart cells to avoid "macromolecular Crowding" in cytosol. The watery portion of cytoplasm helps maintain homeostasis (or biological balance) even though its activity changes significantly between day and night.
Stangherlin explained that "this homeostatic control mechanism protects from variations in cellular volume."
"The intracellular ions increase occurs at the end the rest phase (night for human beings) and allows the heart's beat rate to be increased in preparation for the daily cardiovascular load.
"In heart cells the change in Na and K gradients across plasma membranes is sufficient to drive action potential firing at different times of the day, both in vitro as well as in vivo,"
This finding was made in isolated cardiac cells from mice's hearts. It suggests that circadian rhythms are present at some level in the heart, even if it is not connected to any other parts of the body. This shows how deeply rooted the biological clock really does seem.
John O'Neill, senior molecular biologist and researcher, says that the ways in which heart function changes over time are more complicated than we thought.
It opens up exciting possibilities for more effective treatments of cardiovascular conditions, such as delivering drugs at the correct time of the day.
Further research is possible to determine how these cellular clocks may impact the health of vulnerable individuals, such as shift workers who are often very active at night when their bodies would expect them to sleep.
O'Neill states that "we think that when the circadian clocks of the heart are desynchronized from the brain, such as during shift work," our cardiovascular system may not be able to handle the daily stresses of everyday life."
"This makes the heart more susceptible to dysfunction."
Nature Communications reports the findings.
