July 2, 1999--Many of the body's cells need a reliable flow of potassium to perform their daily tasks. One key to potassium flow, now revealed to researchers, appears to be the energetic effect of a pool of approximately 50 water molecules and four protein spirals that sit in the middle of a narrow channel embedded within cell membranes.
Roderick MacKinnon, a Howard Hughes Medical Institute investigator at The Rockefeller University, and chemist Benoit Roux at the University of Montreal, arrived at this conclusion after calculating the electrical forces operating at the center of the so-called potassium channel. This mathematical analysis follows MacKinnon's team's determination of the three-dimensional structure of a potassium channel last year. The current work appears in the July 2, 1999, issue of the journal Science.
The critical problem facing cells is that potassium -- as well as other small, charged entities known as ions -- would rather be surrounded by water than by the fatty substances that make up the cell membrane. As MacKinnon explained, "these ions are equally stable in the watery environments found inside or outside of the cell, but getting from one side of the cell membrane to the other is like crossing a large mountain.
"The result is that potassium does not cross the cell membrane easily, no matter which direction it has to travel," he added.
Moving potassium through the cell membrane is critical to numerous life-sustaining functions, including nerve signal generation, heartbeat, and insulin release in response to changes in blood sugar. For example, when a nerve signal travels the length of a neuron, large amounts of potassium must be able to flow quickly from the inside to the outside of a cell.
Last year, MacKinnon and his colleagues showed that the potassium channel is
essentially a pore-like structure containing four identical proteins spanning
the thickness of the cell membrane. Their studies r
Contact: Jim Keeley
Howard Hughes Medical Institute