September 22, 2011

First Human Heart Cells Paced with Light

(Ivanhoe Newswire) -- Stanford researchers have created the first human heart cells that can be paced with light, providing new insight into the heart's function.

To create the light-responsive heart cells, the investigators first inserted DNA encoding a light-sensitive protein -- known as ChR2 -- into human embryonic stem cells. ChR2 controls the flow of electrically-charged ions into the cell. The primary ion for heart cells is sodium, which initiates the electrochemical cascade that causes the cell to contract. They then transformed the optogenetically engineered stem cells into cardiomyocytes that respond to light. Stanford researcher Oscar Abilez, M.D., is the first to create optogenetic human heart cells.

Then, using algorithms, the researchers tested their new cells in a computer simulation of the human heart, injecting the light-sensitive cells in various locations in the heart and shining a virtual blue light on them to observe how the injections affected contraction as it moved across the heart.

"In a real heart, the pacemaking cells are on the top of the heart, and the contraction radiates down and around the heart," Ellen Kuhl, Ph.D., was quoted as saying. "With these models, we can demonstrate not only that pacing cells with light will work, but also where to best inject cells to produce the optimal contraction pattern."

Researchers say the development could lead to a new class of novel, light-based pacemakers and genetically-matched tissue patches that replace muscle damaged by a heart attack. They say, one day, bioengineers may be able to induce pluripotent stem cells fashioned from the recipient's own body or similar cell types that can give rise to genetically matched replacement heart cells paced with light, circumventing the drawbacks of electrical pacemakers.

"We might, for instance, create a pacemaker that isn't in physical contact with the heart," co-author Christopher Zarins, M.D., professor emeritus of surgery, was quoted as saying. "Instead of surgically implanting a device that has electrodes poking into the heart, we would inject these engineered light-sensitive cells into the faulty heart and pace them remotely with light, possibly even from outside of the heart."

In the nearer future, researchers say optogenetics will make it easier to study the heart because they can turn cells on and off with light. Scientists may be able to use these tools to induce disease-like abnormalities and arrhythmias in sample tissues to study how to fix them. They say optogenetics could also lead to advances in various neuronal and cardiac disorders including depression, schizophrenia, cerebral palsy, paralysis, diabetes, pain syndromes and cardiac arrhythmias.

SOURCE: Biophysical Journal, September 19, 2011