Phenotype of capillaries in skeletal muscle of nNOS-knockout mice

Abstract

Because neuronal nitric oxide synthase (nNOS) has a well-known impact on arteriolar blood flow in skeletal muscle, we compared the ultrastructure and the hemodynamics of/in the ensuing capillaries in the extensor digitorum longus (EDL) muscle of male nNOS-knockout (KO) mice and wild-type (WT) littermates. The capillary-to-fiber (C/F) ratio (-9.1%) was lower (P ≤ 0.05) in the nNOS-KO mice than in the WT mice, whereas the mean cross-sectional fiber area (-7.8%) and the capillary density (-3.1%) varied only nonsignificantly (P > 0.05). Morphometrical estimation of the area occupied by the capillaries as well as the volume and surface densities of the subcellular compartments differed nonsignificantly (P > 0.05) between the two strains. Intravital microscopy revealed neither the capillary diameter (+3% in nNOS-KO mice vs. WT mice) nor the mean velocity of red blood cells in EDL muscle (+25% in nNOS-KO mice vs. WT mice) to significantly vary (P > 0.05) between the two strains. The calculated shear stress in the capillaries was likewise nonsignificantly different (3.8 ± 2.2 dyn/cm² in nNOS-KO mice and 2.1 ± 2.2 dyn/cm² in WT mice; P > 0.05). The mRNA levels of vascular endothelial growth factor (VEGF)-A were lower in the EDL muscle of nNOS-KO mice than in the WT littermates (-37%; P ≤ 0.05), whereas mRNA levels of VEGF receptor-2 (VEGFR-2) (-11%), hypoxia inducible factor-1α (+9%), fibroblast growth factor-2 (-14%), and thrombospondin-1 (-10%) differed nonsignificantly (P > 0.05). Our findings support the contention that VEGF-A mRNA expression and C/F-ratio but not the ultrastructure or the hemodynamics of/in capillaries in skeletal muscle at basal conditions depend on the expression of nNOS.

GSNOR Deficiency EnhancesIn SituSkeletal Muscle Strength, Fatigue Resistance, and RyR1 S-Nitrosylation Without Impacting Mitochondrial Content and Activity

“…However, we found that capillary density was unaffected in GSNOR -/-TA muscles and that HIF1a transcript was unaffected, whereas HIF1a protein was undetectable (data not shown). These findings agree with a recent study suggesting that the primary source of skeletal muscle NO, nNOSl, is dispensable for capillary density (6). These data suggest that angiogenesis is differentially regulated by GSNOR during skeletal and cardiac muscle development, and they argue against increased capillary density as an important factor in the augmented fatigue resistance of GSNOR -/-mice.…”

Rac1 governs exercise‐stimulated glucose uptake in skeletal muscle through regulation of GLUT4 translocation in mice

“…The mean capillary‐to‐fibre ratio was calculated using ImageJ, version 1.47 (National Institutes of Health, Bethesda, MD, USA) as described previously (Baum et al . ). Image collections and quantifications were performed blinded.…”

Capillary growth, ultrastructure remodelling and exercise training in skeletal muscle of essential hypertensive patients

“…The mean cross‐sectional fibre area was estimated by point counting, and capillary profile density and capillary‐ to ‐fibre (C/F) ratio were calculated, as previously described (Baum et al . ).…”

“…If a particle falls inside of the counting frame and does not cross a forbidden line it is counted, whereas it is not counted if it touches one of the forbidden lines (Weibel 1979). The mean cross-sectional fibre area was estimated by point counting, and capillary profile density and capillary-to-fibre (C/F) ratio were calculated, as previously described (Baum et al 2013).…”