Research published today in Cell disputes a long-standing belief about the consistency of the cell membrane. The new study states cell membrane structure is closer to a semi-solid similar to Jell-O rather than a viscous liquid as prior theories have stated. These results have important implications for understanding of basic cell biology and cell signaling mechanisms, as well as future drug discovery research.
Prior theories held that the membrane acted as a two-dimensional viscous fluid and because it acts as a fluid, that tugging on one side of it would cause flowing of the fluid until the tension was equalized. While many studies have been performed to suggest membranes worked that way, there was little experimental evidence in actual cell membranes to support it.
In the current study, researchers at Harvard University set out to test tension transfer in action by developing a fluorescent protein that would light up as the signal moved through the membrane. These probes were used to pull on one side of the cell and look for changes in signaling, but to the researchers’ surprise, no such changes were observed even after several experiments were performed. This led them to wonder whether prior basic assumptions about cell membranes might be wrong.
They next set up an experiment with a probe on mechanical actuators. The membrane was tugged in two places and tension was measured. In these experiments no effect was observed on one side based on the actions of the other. When the same experiment was performed on a free membrane disconnected from the cell, there was perfect coupling, indicating a difference in a membrane within a cell versus an isolated one.
They hypothesized that these differences are due to the proteins attached to cells’ cytoskeletons. The proteins occupy an estimated 20% of the cell membrane and could greatly change the way the membrane works.
Adam Cohen, a Professor of Chemistry, Chemical Biology and Physics and lead author of the study likens the effect to Jell-O. "A five percent solution of sugar flows just like water, but a five percent gelatin gel doesn't flow at all, because the gelatin strands are tangled up and can't move relative to each other, so water gets trapped because it can't flow through the molecular-sized spaces between the strands," said Cohen. "But if you take clear Jell-O and put a drop of dye on it, the dye molecules will diffuse through it...because the molecules are small enough to squeeze through."
The researchers plan to continue their studies into membrane tension with this new understanding in mind. They believe their findings could someday have implications for disease treatment as signaling is involved in many biological process—neuronal signaling, ion channels, and synaptic receptors all depend on it—and a large number of drugs target trans-membrane signaling.