Force field evolution during human blood platelet activation

Abstract

Contraction at the cellular level is vital for living organisms. The most prominent type of contractile cells are heart muscle cells, a less well known example are blood platelets. Blood platelets activate and interlink at injured blood vessel sites, finally contracting to form a compact blood clot. They are ideal model cells to study the mechanisms of cellular contraction, as they are simple, bearing no nucleus, and their activation can be triggered and synchronized by the addition of thrombin. Here, we study contraction on the example of human blood platelets employing traction force microscopy, a single cell technique that enables time-resolved measurements of cellular forces on soft substrates with elasticities in the physiological range ∼4 kPa). We find that platelet contraction reaches a steady state after 25 min displaying total forces of ∼34 nN. These forces are considerably larger than what was previously reported for platelets in aggregates, demonstrating the importance of a single cell approach for studies of platelet contraction. Compared to other contractile cells, we find that platelets are particular, because force fields are nearly isotropic with forces pointing toward the center of the cell area.