Vergleichende Untersuchungen zur Orientierung von Blutzellen in lebenden Mikrogefäßen

The deformability of red blood cells (RBC) is known to be essential prerequisite for normal blood flow in the terminal vasculatures (pulmonary and peripheral).Until recently, details of the flow behaviour, namely deformation and axial migration of RBC could only be studied in artificial flow systems. In the current dissertation, the flow behaviour of nucleated avian (anser anser), non-nucleated mammalian RBC and artificially altered RBC (rigidified by the exposure to DIAMIDE, a membrane permeant bifunctional SH-oxidant) was studied in the microvasculature of an isolated rat mesentery. The techniques applied (v.i.) allowed to monitor objective Indicators for the hydrodynamic efficiency of the physiological deformability of mammalian RBC. Methods: The studies were executed using the Aachen in vivo Rheoscope, in which a rat mesentery is hydrodynamically isolated, placed into a special flow chamber and placed onto a computer controlled microscope stage. The stage (in X and Y-direction) and the objective (in Z-direction) were displaced by stepper motors in such a fashion that the moving cells could be observed while travelling from arterioles via capillaries to venules. The current report is focussing on behaviour in arterioles (15µm < diameter < 20 µm) during normal perfusion (pressure head 50 to 100 cm H2O). Order parameters quantifying instantaneous position in the velocity profile, orientation of RBC with respect to local vessel axis and cell-cell-distances (RBC-RBC, RBC-Endothelial Cells) were determined off-line from the video-films taken. Results and their Interpretation: The ability of non-nucleated RBC to orient themselves in flow is shown to critically depend on the fluidal state of the cytosole and the shear compliant properties of the membrane. In comparison to avian cells on the one hand, and to rigidified human cells on the other, the orientation of normal human RBC in the natural flow field is significantly more stable: they have a permanent orientation and - due to axial drift - avoid trajectories in close proximity to the endothelial cells. Lastly, in normal human RBC cell-cell-contacts and cell - wall - contacts are significantly less frequent. While avian nucleated RBC are preferentially oriented, they occasionally rotate and subsequently can show much "clustering" due to collisions. Mildly rigidified DIAMED rigidified human RBC incessantly jumble, i.e. are neither well oriented nor do they remain in the axial stream. It has previously been established that in the doses applied (1.5 mMol/30 min exposure) DIAMID acts exclusively by cross-linking the intrinsic membrane proteins, rendering to them the behavioural traits of a "shear elastic shell" (whereas normal RBC membranes are devoid of relevant shear elasticity). The data now reported show that even mild forms of membrane stiffening, in becoming the reason for irregular "tumbling" movements of the afflicted RBC, prevents the self-fluidizing behaviour traits of normal mammalian RBC, thus providing an important clue concerning the interdependency of submicroscopic ("molecular") causes and microscopic ("cellular") and macroscopic (network associated) effects in all vessels of the microcirculation