Cell transit analysis of ligand-induced stiffening of polymorphonuclear leukocytes.

A mathematical treatment of the mechanical behavior of transiently bonded polymer networks is used to interpret measurements of the pressure-induced passage of plant cells through microporous membranes. Cell transit times are inferred to be proportional to the instantaneous shear modulus of the cell cortex, a parameters that we then relate to properties of the cortical F-actin matrix. These theoretical results are used to analyze published data on chemoattractant-induced changes of rigidity of polymorphonuclear leukocytes. We thereby rationalize previously noted, peculiar, power-law logarithmic dependences of transit time on ligand concentration. As a consequence, we are able to deduce a linear relationship between the extent of F-actin polymerization and the logarithm of the chemoattractant concentration. The latter is examined with regard to the G-protein activation that is known to occur when chemoattractants bind to receptors on the surfaces of polymorphonuclear cells.