Influence of trypsin on the dynamic mechanical properties of intact RBC membrane

AIM: To study the influence of trypsin on the membrane dynamic mechanical properties and the surface charge density of single living intact red blood cell (RBC). METHODS: Young and old RBCs were separated from health adult human blood using the density gradient centrifugation. Then RBCs at different ages were incubated with trypsin at different concentration at 37 ℃ for 60 min. The surface negative charge density of RBCs was determined using ZetaPLUS potential analyzer. The size and membrane bending elastic modulus (Kc) and shear elastic modulus (μc) were determined by fast micro-image analyzing technology. RESULTS: (1) The surface negative charge density of normal and trypsin-treated old RBCs was significantly lower than those of normal and trypsin-treated young RBCs respectively (P<0.01). (2) The contact area of normal old RBCs was significantly smaller than that of normal young RBCs(P<0.05), but there was no difference in shape between normal young RBCs and normal old ones. Trypsin reduced the size of RBCs but did not affect the shape and size of both young and old RBCs. (3) The Kc and μc of normal old RBCs membrane were markedly larger than those of normal young RBCs respectively (P<0.05). The Kc and μc of young and old RBCs membrane were both increased at different concentration of trypsin. CONCLUSION: The surface negative charge density of young and old RBCs decreases, and the membrane elastic modulus of young and old RBCs membrane increases after treatment with trypsin. Therefore, the mechanical deformability of RBCs membrane is reduced.