Evidence for role of capillaries in regulation of skeletal muscle oxygen supply

How oxygen (O 2 ) supply to capillaries is regulated to match the tissue's demand is unknown. Erythrocytes have been proposed as sensors in this regulatory mechanism since they release ATP, a vasodilator, in an oxygen saturation (SO 2 )‐dependent manner. ATP causes hyperpolarization of endothelial cells resulting in conducted vasodilation to arterioles. Objective We propose individual capillary units can regulate their own O 2 supply by direct communication to upstream arterioles via electrically coupled endothelium. Methods To test this hypothesis, we developed a transparent micro‐exchange device for localized O 2 exchange with surface capillaries of intact tissue. The device was fabricated with an O 2 permeable micro‐outlet 0.2 × 1.0 mm. Experiments were performed on rat extensor digitorum longus (EDL) muscle using dual wavelength video microscopy to measure capillary hemodynamics and erythrocyte SO 2 . Responses to local O 2 perturbations were measured with only capillaries positioned over the micro‐outlet. Results Step changes in the gas mixture %O 2 caused physiological changes in erythrocyte SO 2 , and appropriate changes in flow to offset the O 2 challenge if at least 3–4 capillaries were stimulated. Conclusion These results support our hypothesis that individual capillary units play a role in regulating their erythrocyte supply in response to a changing O 2 environment.