Skin cells emit slow electric pulses after injury

Wounded skin cells scream with slow-motion electric pulses.

Such electric spikes are a surprise because only nerve cells were thought to communicate this way. These signals move at a snail’s pace compared to nerve impulses and can be detected at least 500 micrometers away — about the distance of 40 cells — researchers report in the March 25 Proceedings of the National Academy of Sciences. The pulsing electrical waves may help injured cells’ neighbors prepare to heal wounds.  

For over 150 years, scientists have known that wounds alter electric fields across skin cells, says cell biologist Min Zhao of the University of California, Davis School of Medicine. But they didn’t know that skin cells can send spikes of electricity the way nerve cells do, says Zhao, who was not involved with the new work.

To capture this phenomenon, bioengineer Sun-Min Yu and engineering scientist Steve Granick — both of the University of Massachusetts Amherst — grew human skin cells or dog kidney cells on electrode-lined chips. Both are epithelial cells, a cell type that forms barriers such as skin and mucous membranes, and also lines organs and body cavities. After blasting some cells with lasers, Yu measured tiny shifts in electrical activity.

The researchers found that the pulses generated by both the skin and kidney cells are partly driven by the flow of calcium ions and have about the same voltage as a nerve cell zap. But the spikes move at a crawl compared to nerve cell signals, Granick says. Whereas nerve cell impulses last just milliseconds, epithelial cells take one to two seconds to spit out their electrical messages.

The process was so pokey that Yu nearly missed the signals. “She realized she would just [have to] be patient and make measurements over a glacial scale,” Granick says.

The software Yu was using was set to detect speedier nerve cell pulses and wouldn’t flag spikes slower than 500 milliseconds. “I asked the software engineer to release that constraint, and then it worked,” Yu says.

Wounded cells sent pulses for more than five hours, possibly alerting their neighbors to squeeze out damaged cells and to start replicating to repair the wound. Such slow, long-lasting signaling makes sense, Zhao says. While nerve cells drive split-second reactions, epithelial cells heal wounds over days to weeks.

The discovery of these electrical spikes adds a new understanding of the time dimension of the wound healing process, Zhao says. And it may give researchers new respect for the role of electrical activity. Electric fields are often dismissed as less important than biochemical or mechanical signals. “We need to change that idea,” Zhao says. “We also need to understand [wound healing] as a complicated, complex process involving many different aspects,” including short bursts of electrical activity.

The study looked at electrical propagation only in roughly two-dimensional sheets just one cell thick. Yu hopes to next explore how epithelial cells use these pulses to communicate in 3-D structures and with other cell types.