Kidney cells don't filter blood, they pump it
Human kidneys are an intricate network of tubes that process roughly 190 quarts of blood every day. Lining these tubes are epithelial cells that transport blood through the kidneys and circulate it back into the body.

The researchers noticed that kidney epithelial cells behave like mechanical fluid pumps and actively generate a fluid pressure gradient. The fluid pumping behavior is characterized by a pump performance curve, which is very much like a water pump in a house. Most people believe that kidneys behave like a conventional filter, which needs external pressure to move fluid. However, research team showed that cells can actually generate the needed pressure themselves—an insight with important implications for understanding kidney physiological function.

also used the device to examine mechanical behaviors of kidney epithelial cells from patients with autosomal dominant polycystic kidney disease, or ADPKD. ADPKD is a common inherited and aggressive disorder in which the kidney develops fluid-filled cysts, resulting in an enlarged kidney. The team's device showed that ADPKD cells pump fluid in the opposite direction of healthy epithelial cells. This altered pumping behavior changes the kidney tube's pressure profile, resulting in change to their shape and morphology.

They also tested the drug Tolvaptan on ADPKD cells using their micro-fluidic kidney pump. Tolvaptan is an FDA-approved drug that helps delay ADPKD disease progression. The team showed that ADPKD cells responded to the drug by lowering the fluid pumping flux and pressure gradients, which means the cyst should develop more slowly.

Source: https://www.nature.com/articles/s41467-022-29988-w
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