Researchers Just Found That Kidneys Act on Blood Differently Than We Thought Before

By this time tomorrow, every drop of blood in your body will have passed through your body many times. Water saturated with waste is removed to form urine and fresh blood is returned to circulation.

The vital task might be seen as a kind of force-fed filtration driven by our heartbeat. According to a new study co-authored by Sean Sun, that description is not as accurate as previously thought.

Sun says that everyone hears that the kidneys filter blood, but that is incorrect.

We showed that the cells of the kidneys are generating forces.

We missed this peculiar mechanical activity because we looked at it. Since the 17th century, anatomists have known about the structure and function of the kidneys.

Inside and outside of the body, the organ's ability to mix passive physics of osmosis with active sucking of various chemicals has been studied.

It's possible that the channels and tubules crammed into a space no bigger than your fist make for some weird plumbing inside.

Studies have shown that the cells lining those tubules can sense changes in pressure, but it is not clear how or if those changes push back in some way.

It is not easy to work out how fluids get into those pipes. It would take a lot of technology to screen out stray forces in an experiment to study the hydraulics inside individual tubules.

Sun and colleagues from across the US came up with that. The micro-fluidic kidney pump has patterned blocks and porous membranes that can hold a culture of cells.

When the cells had settled into place and were subjected to a range of tests for electrical resistance and permeability, the researchers measured variations in pressure across the tissue.

The movement of fluids near the cells was affected by a rise in the pressure on the tissue. We would expect the tubules to act like a pump.

Changes in the pressure of fluids entering the tissues changed the arrangement of ion channels and their supporting structure, as revealed by a close look at the proteins the cells were making.

For most of us, this means fluids passing from the blood into the kidney&s network of tubules moves in part under the mechanical direction of the cells themselves, adding a subtle new layer of operation that could help to explain a range of renal disorders.

The researchers used cells from people with the disease to see how this behavior unfolds inside the less-functional kidneys.

In this condition, the cells lining the tubules change shape, causing cysts to form, and raising the risk of urinary tract infections. According to the team's work, there is more to the story.

When the FDA-approved treatment tolvaptan was applied to the cells, their pressure was smoothed out, suggesting the drug works by reducing stress on the tissues and slowing the rate at which cysts might form.

It is possible that other tissues have their own versions of a mechanical pumping system. Sun and his team want to modify their device to test other tissues.

Nature Communications published this research.