New Method Lets Researchers Study Heart Cell Communication

Research Associate Barbara J. Muller-Borer, Ph.D., and her colleagues in the Division of Cardiology at UNC's Department of Medicine used a technique called fluorescence recovery after photobleaching, or FRAP, to study cell-to-cell communication through tiny tunnels between cells called gap junctions.

She will present the work at the North American Society of Pacing and Electrophysiology conference in Boston on May 4.

"You take a fluorescent probe, load it into your cells, and shine a laser pulse on some of them," Muller-Borer said. The laser makes the probe stop glowing, and the laser-zapped cells stop glowing.

As the fluorescent probe from surrounding cells diffuses in through gap junctions, fluorescence recovers and the zapped cells begin to glow again.

"The time it takes for the cell to recover fluorescence would be an indicator of how well the cells are coupled," or connected to each other, Muller-Borer said.

Coupling is important in heart muscle cells because the electrical signal that causes the heart to beat travels through them. If they become uncoupled, you're not going to get electrical conduction through that tissue, and the heart will stop beating, Muller-Borer explained. Heart muscle cells can become uncoupled when their oxygen supply is cut off, as happens during a heart attack.

Other researchers have used voltage-sensitive dyes to study the flow of electrical signals through heart tissue.

"The problem with some of those dyes is they're pretty toxic," Muller-Borer said. "So once you flash the cells with the laser, the dyes become toxic and the cells die. So you get one good study and then they're dead." FRAP allows researchers to study cells over longer periods of time, Muller-Borer said.

FRAP is an alternative method to study cell-to-cell communication. "The classic way to do these experiments is with electrical measurements," said Wayne Cascio, M.D., Associate Professor of Medicine at UNC's Division of Cardiology and one of the study's authors. "You inject a current into the muscle and you measure the voltage between two electrodes along the path of that current flow. Gap junctions affect that voltage."

But electrodes are not useful for studying how gap junctions work at the cellular level, Cascio said. "So this would provide a way to look at cell-to-cell communication at the level of single cells in cultures of heart cells.

"We're also interested in using FRAP to study how common diseases such as hypertension, ischemic heart disease and heart failure affect the formation and function of gap junctions," Cascio added. "The number and distribution of gap junctions are affected by these conditions and may contribute to some of the adverse consequences of these diseases. For this reason, we expect that the FRAP technique will further our understanding of how cell-to-cell communication contributes to heart problems."

This research was supported by a grant from the National Institutes of Health and the American Heart Association.