Final answer:
The focal complexes near the leading edge of a motile cell exert traction force through their associated actin cytoskeleton and can either disassemble or mature into contractile focal adhesions. These adhesions transmit forces to the substrate and are stabilized by contractile stress fibers and external forces, playing a key role in cell motility and mechanosensing.
Step-by-step explanation:
The focal complexes that form near the leading edge of a motile cell exert traction force through their associated actin cytoskeleton and then typically disassemble as the cell moves forward or mature into larger, more contractile focal adhesions. These focal adhesions are dynamic structures critical for cell movement. They are capable of transmitting forces to the substrate through the process of traction force microscopy on flat elastic substrates, reflecting a linear coupling between force and protein assembly within the adhesions, equating to a constant stress of about 5 nN/nm² or 5 kPa.
Additionally, the adhesions must endure sufficient force not only from contractile stress fibers, connected to actomyosin contractility, but also from other sources like retrograde flow or external mechanical forces, for stability and maturation. Focal adhesions are inherently linked to the matrix surrounding the cell, which suggests a potential use in mechanosensing within a cell's physiological context.
Cells utilize these complexes and their interaction with stress fibers, to not only physically adhere to surfaces but also to sense their surroundings and adjust their adhesion strength accordingly. This process is influenced by various forces, including those from the actin-myosin interactions, which highlights the importance of physical forces in regulating focal adhesion dynamics and cellular adhesion overall.