Visualisation of capillaries in human skeletal muscle

A double staining method combining Ulex europaeus agglutinin I lectin (UEA-I) and collagen type IV staining was used to determine the capillary density and the number of capillaries relative to different fibre types in human skeletal muscles. The result of this combined staining was compared with that of other staining methods including amylase-periodic acid Schiff (PAS), UEA-I, anti-collagen type IV and anti-von Willebrand factor. Muscle biopsy specimens, 12 from M. vastus lateralis and 6 from M. soleus, were obtained from 18 healthy young men. Compared with amylase-PAS staining, double staining showed a larger number of capillaries surrounding type I (+9.6%), type IIA (+8.6%) and type IIB (+11.6%) fibres in the M. vastus lateralis specimens (P<0.001 for all differences). The capillary to fibre ratio (cap . fibre(-1)) and the capillary density (cap . mm(-2)) were 8.3% (P<0.002) and 7.9% (P<0.001) larger, respectively. In the M. soleus specimens, cap . fibre(-1) and cap . mm(-2) were 7.4 and 9.9% larger, respectively, by double staining compared with PAS staining. Further comparisons showed that the cap . fibre(-1) and cap . mm(-2) obtained with double staining were similar to the values determined by the UEA-I staining, but greater than that measured by the collagen type IV method. The double staining gave a more marked stain of capillaries and revealed muscle fibre borders clearly, which is an advantage in studies that require comparisons between serial sections using computerised image analyses. It is concluded that the double staining method is superior to either the UEA-I, collagen type IV or the traditional amylase-PAS staining methods in analysing capillary density of normal human skeletal muscle.