A new study confirms directly what scientists previously knew only indirectly: The poisonous "rotten egg" gas hydrogen sulfide is generated by our body's growing cells. Hydrogen sulfide, or H2S, is normally toxic, but in small amounts it plays a role in cardiovascular（心血管的） health.

In the new study, chemists developed a chemical probe that reacts and lights up when live human cells generate hydrogen sulfide, says chemist Alexander R. Lippert, Southern Methodist University, Dallas. The discovery allows researchers to observe the process through a microscope.

The researchers captured on video the successful chemical probe at work, said Lippert, an assistant professor in the SMU Department of Chemistry.

"We made a molecular probe that, when it reacts with hydrogen sulfide, forms a fluorescent compound that can be visualized using fluorescence microscopy," Lippert said. "This is the first time that endogenously（内生地） generated hydrogen sulfide has been directly visualized in a living system. This confirms a lot of hypotheses that scientists have, but no one had the tools to directly detect it in real time."

H2S is one of several small gaseous molecules increasingly recognized as key signaling molecules in the body. For example, H2S helps reduce high blood pressure. Scientists discovered in the past decade that cells in the human body generate small quantities of H2S molecules, which in turn deliver information to proteins. The proteins act on the information to perform critical functions in the body.

Previously, scientists couldn't observe H2S being generated in live cells. As a result, researchers faced challenges when studying hydrogen sulfide in living systems, Lippert said. The new discovery now provides a tool to view directly how and when hydrogen sulfide is generated, he said. Lippert and study co-author chemist Vivian S. Lin made the discovery.

Discovery provides research tool for scientists to observe H2S in live cells 

"Having the tools to do this in living systems is going to open up a lot of possibilities and experiments for scientists," Lippert said. "As a tool, this will allow researchers to ask questions that weren't possible before."

Lippert's real-time video features live human cells, taken from the lining of blood vessels and treated with the chemical probe and with a protein known to promote cell growth. Once the cells start generating H2S, they behave like squiggly fluorescent green worms.

The researchers' scientific article, "Cell-trappable fluorescent probes for endogenous hydrogen sulfide signaling and imaging H2O2-dependent H2S production," was published online in the Proceedings of the National Academy of Sciences.