How shrews and other tiny creatures have superfast heartbeats

Do you ever stop to marvel at the tireless beating of your heart, rhythmically pulsating at an average pace of 60 to 100 beats per minute? Now, try to imagine an organism, considerably tinier than our species, whose heart goes on a racing spree at around 1,020 beats per minute. Nope, this isn’t a hyperbole; it’s the humble shrew, a creature no bigger than your index finger with incredible hearts.

Enigma of nature’s artistry

The resting heart rate of a shrew reaches up to 17 beats per second, making it about 10-17 times faster than that of us humans.

This biological marvel has intrigued scientists for years – how does such a tiny creature manage to maintain a heart rate that would be lethal for most species?

This question has finally found an answer in a recent study published in the prestigious journal, Science.

Mystery of shrew’s heart

An international team of researchers, led by postdoc William Joyce during his time at Aarhus University (AU), and his colleague, Professor Kevin Campbell, previously of AU and currently with the University of Manitoba (Canada), embarked on this mission to decode the shrew’s heart.

It was during this investigation that they discovered the secret lay in the heart protein called “cardiac troponin I.”

“We discovered that a crucial part of the heart protein that regulates heart relaxation time is missing in shrews and closely related moles,” explains Joyce, who has shifted his base to The Centro Nacional de Investigaciones Cardiovasculares Carlos III (CNIC) in Spain.

“This evolutionary loss permanently removes the brakes on heart relaxation, allowing their hearts to beat much faster.”

Missing link in the protein chain

The protein cardiac troponin I is integral to the way a heart works. It binds to calcium ions during contraction, a process pivotal for the heart muscle’s function.

In most mammals, this protein contains two specific serine amino acids that are temporarily modified when the heart gets a burst of adrenaline from stress or physical activity.

This modification allows the heart to relax faster between beats, providing more time for blood refill, thus setting the pace for the next contraction.

But a remarkable deviation occurs in the case of shrews.

“In an early ancestor of shrews, the DNA region encoding the two serines became inactivated. This means the protein always functions as if it were activated by adrenaline, even when the animal is at rest, allowing shrews to achieve their extreme heart rates,” explains Campbell.

Shrews, bats and their heart rates

To understand how this evolution towards high heart rates has unfolded, the research team studied the heart protein in bats. Like shrews, bats also boast heart rates exceeding 1,000 beats per minute.

“Our analysis shows that some bat species can skip over the part of the gene that codes for the two serine amino acids when the protein is formed,” Campbell continued.

Ancient shrews and moles likely had the same ability, and evolution gradually favored their troponin I proteins to completely lose this region. This permitted them to evolve even higher heart rates.

Implications for humans

The findings about the shrew’s cardiac adaptations provide intriguing insights into the potential avenues for advancing human health and medicine.

Understanding how the removal of the regulatory serine amino acids leads to enhanced heart rate capabilities in shrews could inspire new therapeutic strategies aimed at treating heart conditions in humans.

For instance, manipulating similar pathways could help develop treatments that ameliorate conditions marked by slowed or inefficient heartbeats.

By revealing how nature adapts efficiently under high metabolic demands, these discoveries might pave the way for medical innovations that can mimic these natural developments for human benefit.

Future research on shrew’s heart

This research not only elucidates the evolutionary paths taken by shrews and bats but also opens new frontiers in cardiovascular research.

Future studies could delve deeper into the genetic and molecular underpinnings that enable such high heart rates, potentially harnessing these mechanisms for translational applications.

Continued exploration into the genetic coding of cardiac proteins across different species may uncover more evolutionary strategies that have yet to be understood, shedding light on the diversity and adaptability of life on Earth.

By investigating these natural adaptations, scientists may unlock new strategies for improving heart function, offering unprecedented insights into both human health and evolutionary biology.

Potential implications for biomedicine

The findings from this study are not just fascinating trivia about tiny mammals like shrews and their heart rate. They may have far-reaching implications for the field of biomedicine.

“Our goal is to translate our findings into biomedicine. This means replicating the splicing of troponin I, as observed in bats, in model organisms and potentially — eventually — in human hearts to mimic the beneficial effects,” Joyce comments.

Indeed, the implications of this research stretch far and wide, from a deeper understanding of the heart’s mechanics to possibly revolutionizing biomedical strategies.

It’s a stark reminder of how much we can learn from the smallest creatures whose hearts have lessons to teach us far beyond our own human pace.

The study is published in the journal Science.

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