Effect of Diabetes on Microvascular Morphology and Permeability of Rat Skeletal Muscle: In Vivo Imaging Using Two-Photon Laser Scanning Microscopy.

This investigation evaluated the microvascular permeability and ultrastructure of skeletal muscle capillaries in skeletal muscle of diabetic (DIA) rats using two-photon laser scanning microscopy (TPLSM) and transmission electron microscopy (TEM). Microvascular permeability was assessed in the tibialis anterior muscle of control (CON) and DIA (streptozocin) male Wistar rats (n = 20, 10-14 wk) by in vivo imaging using TPLSM after fluorescent dye intravenous infusion. Fluorescent dye leakage was quantified to determine microvascular permeability. The ultrastructure was imaged by TEM ex vivo to calculate the size and number of intercellular clefts between capillary endothelial cells and also intracellular vesicles. Compared with control, the volumetrically determined interstitial fluorescent dye leakage, the endothelial cell thickness, and the number of intercellular clefts per capillary perimeter were significantly higher, and the cleft width was significantly narrower in TA of DIA (interstitial fluorescent dye leakage, 2.88 ± 1.40 vs. 10.95 ± 1.41 µm³ x min x 10⁶; endothelial thickness 0.28 ± 0.02 vs. 0.45 ± 0.03 µm; number of intercellular clefts per capillary perimeter 6.3 ± 0.80 vs. 13.6 ± 1.7 /100 µm; cleft width 11.92 ± 0.95 vs. 8.40 ± 1.03 nm, CON vs. DIA respectively, all p <0.05). The size of intracellular vesicles in the vascular endothelium showed an increased proportion of large vesicles in the DIA group compared to the CON group (p < 0.05). Diabetes mellitus enhances the microvascular permeability of skeletal muscle microvessels, due, in part, to a higher density and narrowing of the endothelial intercellular clefts, and larger intracellular vesicles.