Each heartbeat results from the concerted action of millions of heart muscle cells. If researchers understood better how heart disease affects the individual cells, they might be able to detect early signs of trouble. Now Gisela Lin, an electrical engineer at UCLA, has created a microscopic instrument that can measure how much force a single heart cell exerts when it contracts.
Lin’s measuring device, which is less than a tenth of an inch square, consists of a pair of silicon clamps suspended on delicate beams from the edge of a silicon chip. The device is lit from below, so that when Lin affixes the clamps to a rat’s heart cell she can observe it through a microscope and project an image of it onto a video monitor. To keep the cell alive she submerges the entire device in a saline solution.
Like other muscle cells, heart cells are permeated by alternating bands of two proteins, actin and myosin. Myosin is the molecular motor of muscle contraction: when it receives a particular chemical signal, it tugs on actin. The myosin sticks to the actin molecules and pulls on them, so that the whole cell ratchets inward, says Lin. In Lin’s device, the contraction of the clamped cell bends the two silicon beams; the amount of bending shows how much force the cell is exerting.
The average force, Lin has found, is between 10 and 20 micronewtons--roughly equal to the weight of 10 to 20 grains of salt. Right now Lin measures the force by simply measuring the deflection of the silicon beams on her video monitor, but she’s also working on a more accurate system that will translate the bending into a voltage signal.
With enough data, the device should be able to tell the difference between normal and diseased heart cell contractions and help researchers better understand the basis of heart disease. The goal is better understanding of the mechanism of the heart, says Lin. If we can understand what’s going on at the cellular level, then we’re hopeful we can extrapolate to what’s going on in the entire heart.
