Fiber capillarization relative to mitochondrial volume in diaphragm of shrew

The objective was to examine fiber capillarization in relation to fiber mitochondrial volume in the highly aerobic diaphragm of the shrew, the smallest mammal. The diaphragms of four common shrews [Sorex araneus; body mass, 8.2 ± 1.3 (SE) g] and four lesser shrews (Sorex minutus, 2.6 ± 0.1 g) were perfusion fixed in situ, processed for electron microscopy, and analyzed by morphometry. Capillary length per fiber volume was extremely high, at values of 8,008 ± 1,054 and 12,332 ± 625 mm−2 inS. araneus and S. minutus, respectively (P= 0.012), with no difference in capillary geometry between the two species. Fiber mitochondrial volume density was 28.5 ± 2.3% (S. araneus) and 36.5 ± 1.4% (S. minutus;P = 0.025), yielding capillary length per milliliter mitochondria values (S. araneus, 27.8 ± 1.5 km;S. minutus, 33.9 ± 2.2 km; P = 0.06) as high as in the flight muscle of the hummingbird and small bats. The size of the capillary-fiber interface (i.e., capillary surface per fiber surface ratio) per fiber mitochondri...