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

UNLABELLED

How oxygen (O ) 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 )-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 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 exchange with surface capillaries of intact tissue. The device was fabricated with an O 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 . Responses to local O perturbations were measured with only capillaries positioned over the micro-outlet.

RESULTS

Step changes in the gas mixture %O caused physiological changes in erythrocyte SO , and appropriate changes in flow to offset the O 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 environment.