Capillary endothelial cell heterogeneity in skeletal muscle of female and male mice.

In skeletal muscle, capillaries have been shown to be critical to active hyperemia by sensing skeletal muscle activity and directing blood flow to contracting muscle fibers. There is evidence to suggest that capillary endothelial cell (EC) characteristics may change along the length of a capillary. This longitudinal heterogeneity may have implications on capillary function with respect to their role in active hyperemia. We sought to determine whether EC characteristics differed along the length of a capillary. We perfused 5 female and 6 male CD-1 mice with fluorescently labeled Wheat Germ Agglutinin (WGA) and GS-IB4 Isolectin (ISO) which bind to different carbohydrate sites on the EC glycocalyx. We imaged capillaries along their length in fresh whole mounts of the gluteus maximus, diaphragm, soleus, extensor digitorum longus, and cremaster muscles. We observed that WGA labeled capillaries across their entire length while ISO only stained the arteriolar end of capillaries. These findings were observed in all muscles in females and males. These data show that the constituents of the capillary EC glycocalyx are not consistent across the length of a capillary. This capillary heterogeneity may have important implications for the microvascular response during active hyperaemia and blood flow control during muscle contraction.