A chemotactic relationship between skeletal muscle nuclei and capillaries

The vascular beds of femoral biceps, soleus, and medial gastrocnemius of the rat were perfused with India ink to outline the capillary network. Histologic cross sections were stained with picric acid and basic fuchsin. By this method, the muscle fiber nuclei appeared red and could be clearly distinguished from the darker-stained capillary profiles. A specific anatomic relationship between capillaries and muscle fiber nuclei was tested against a random orientation by an analysis of independence. Systematic sampling was performed by positioning the center of an eyepiece reference circle on the uppermost point of each fiber profile. The frequencies of the four combinations (fiber nuclei and/or capillaries or neither) found within each test circle were recorded and stored in 2 × 2 contingency tables. The Z test of independence revealed a highly significant relationship between capillaries and fiber nuclei in all muscles examined. The nonrandom nucleus-related location of capillaries around muscle fibers was even more evident after pooling the individual muscle data in a single table ( P ⪡ 0.00001). These findings suggested a chemotactic attraction of capillaries by the muscle fiber nuclei. This observation is supported by the high concentration of cytoplasmic organelles present in nuclear regions of skeletal muscle fibers, that is well documented in the literature. These organelles may be responsible for the production and local secretion of chemotactic factors “to attract” capillaries, and hence provide for their characteristic orientation and distribution in muscle.