EVIDENCE THAT CELL-SURFACE CHARGE REDUCTION MODIFES CAPILLARY RED-CELL VELOCITY-FLUX RELATIONSHIPS IN HAMSTER CREMASTER MUSCLE

1. From capillary red cell velocity (V)-flux (F) relationships of hams ter cremaster muscle a yield velocity (V-F=0) can be derived at which red cell flux is zero. Red cell velocity becomes intermittent and/or r ed blood cells come to a complete standstill for velocities close to t his yield velocity, and, at the same time, capillary tube haematocrit becomes very low. 2. We have tested whether the net negative charge of red blood cells (RBCs) contributes to the magnitude of V-F=0. Velocit y-flux relationships were measured for normal cells, normal cells labe lled with the fluorescent dye calcein (LRBCs), and red cells treated w ith hexadimethrine to mask negative charge and labelled with calcein a s well (HDM-LRBCs). Measurements were done in a hamster cremaster musc le preparation applying video in, vivo microscopy. 3. Hexadimethrine t reatment reduced the net negative surface charge of red cells to 20% o f control as estimated from transmission electron microscopy using a f erritin tagging technique. The values of V-F=0 found for normal red ce lls and HDM-LRBCs were 86 +/- 15 and 31 +/- 1.7 mu m s(-1), +/- S.E.M. , n=12, respectively, which were significantly different (P<0.05). For normal cells and cells labelled with calcein only, V-F=0 values were 63 +/- 14 and 65 +/- 13 mu m s(-1), n=8, respectively, which were not significantly different. The effect of HDM treatment did not alter fil terability of the red cells as estimated from transit times through 5 mu m pores. 4. The present findings demonstrate that the net negative charge of RBCs contributes significantly to the yield velocity for red blood cells entering capillaries and flowing through them. HDM treatm ent reduced the net negative charge of red blood cells and may have ca used cells to enter capillaries more easily owing to reduced electrost atic repulsion at the capillary entrance. In addition, HDM treatment m ay have lowered intracapillary flow resistance by a reduction in elect rostatic repulsive forces between red blood cells and negatively charg ed (macromolecules on) capillary endothelial cells at sites of irregul ar capillary cross-sectional shape, without significantly affecting th e lubricating properties of the capillary endothelial glycocalyx and/o r associated plasma macromolecules.