Alternative histochemical markers for skeletal muscle capillaries: a statistical comparison among three muscles

Except in thin muscles, the analysis of muscle capillary depends on direct ultrastructural visualization or histochemical identification of the capillaries using stains for basement membrane or reactions for endothelial cell enzymes. The accuracy of existing histochemical methods for detecting capillaries has not been systematically tested, however. The purpose of the present study was to compare muscle capillarity determined by two methods currently in use, Griffonia simplicifolia I lectin (GSI) and ATPase, with two alternative capillary markers, Lycopersicon esculentum lectin (LEA) and MRC OX.43 antigen. Capillarity, expressed as capillaries around fibers (CAF), was determined in the soleus, extensor digitorum longus, and sternomastoid muscles from 4-month-old female rats. The GSI, LEA, and MRC OX.43 capillary markers gave identical results for each muscle, confirming their validity as cytochemical probes. In contrast, the capillary ATPase method gave significantly lower CAF determinations, with a differential effect of preincubations at pH 4.4 vs 4.0. These data suggest that capillary ATPase acid stability varies within the capillary bed. The use of one or more of the alternative capillary markers tested is suggested for studies of muscle capillarity to confirm that binding sites or enzyme activity used for a given probe is expressed under both control and experimental conditions.