Microrheological assessment of the viscoelastic properties of the endothelial glycocalyx in cremasteric capillaries of living mice

Abstract

The endothelial glycocalyx forms a gel-like compartment inside the vasculature, of which the glycosaminoglycan hyaluronan (HA) forms a major constituent. We used microrheology to measure the viscoelastic properties of the glycocalyx in vivo. With an optical tweezers intravital microscopic setup we were able to trap platelets inside mouse cremaster capillaries, and with laser-interferometry to measure the frequency behavior of their Brownian motion. The slope of power spectra taken in the center of the capillary lumen (−1.97 [SD 0.03] V^2/Hz^2) is consistent with the behavior a purely viscous fluid (slope = −2). In contrast, the greater slope of power spectra in the glycocalyx (−1.87 [SD 0.04], n=4, p < 0.05), is representative of an elastic component near the vessel wall (slope > −2). Light dye (LD) induced damage of the glycocalyx reversed the slopes of near wall power spectra to −1.96 (SD 0.02), indicating normalized viscous behavior of plasma in the absence of the glycocalyx. An in vitro HA concentration higher than 1 mg/ml was needed to simulate a viscoelastic behavior comparable to that of the glycocalyx, which is at least a 1000 times higher than physiological plasma HA levels. In conclusion, this study reports for the first time on the microrheological properties of the glycocalyx in capillaries of living mice and demonstrates that its viscoelastic behavior resembles that of a relatively high hyaluronan concentration. Financial support by the Royal Netherlands Academy of Arts and Sciences (Fellowship to HV) and The Netherlands Heart Foundation (Established Investigatorship 2005T037 to HV) is greatly appreciated.