Muscle contraction is driven by two types of protein filaments: thin carbon actin filaments and thick myosin filaments that act as molecular motors. At rest, a special protein safety catch, tropomyosin, blocks the myosin-binding sites on actin. A nerve impulse triggers the release of calcium ions, which bind to troponin, causing tropomyosin to shift and exposing active sites on actin for myosin heads. However, activation is not a single event: the first myosin head to attach performs its power stroke, shifting the actin filament, and this mechanical displacement, like flipping a tiny magnet, induces conformational changes in neighboring regulatory complexes, making them available for the next motors.
Physicists have described this process using a model of interacting magnetic moments in a chain: as soon as one element reorients, its neighbors pick up the change, and a cascade propagates through the system, directly linked to changes in entropy — a measure of system order.
The drug Omecamtiv mecarbil disrupts this magnetic roll call: it selectively stabilizes the myosin state, preventing the activating signal from propagating along the actin filament. As a result, neighboring regulatory units no longer 'feel' each other, cooperativity drops, and contraction weakens. All these events unfold in the watery environment of the cell, where hydrophobic and electrostatic interactions finely tune molecular mechanics.
One gram of muscle tissue can generate a force of up to 30 newtons — roughly enough to hold a three-kilogram dumbbell with one finger. This is the result of the synchronized work of millions of molecular motors.
Fantastic tales of artificial muscles made from carbon nanotubes come a little closer to reality thanks to such models.