University of Pennsylvania School of Medicine researchers say they've modified a honeybee venom toxin called tertiapin, or TPN, so it can be used to study the workings of ion channels that control heart rate and the recycling of salt in kidneys. In general, ion channels selectively allow the passage of small ions such as sodium, potassium, or calcium into and out cells.

Led by Dr. Zhe Lu, a professor of physiology, the scientists are focusing on TPN's influence on inward-rectifier potassium channels, or Kir channels. TPN stops the flow of potassium ions across cell membranes by plugging Kir channels on the outside of cells, the researchers said.

"The clue comes from patients with genetic defects in these channels who lose a lot of sodium because it cannot be effectively reabsorbed and thus have low blood pressure," said Lu. "An inhibitor specifically against these kidney channels will allow this idea to be tested."

The research that included Yajamana Ramu and Yanping Xu appears in the Proceedings of the National Academy of Science.